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Ultrafine Y2O3:Eu3+ phosphors were prepared by a modified solution combustion method. The as-prepared samples with sizes of 17.6–80 nm (nanophosphors) and 300 nm (submicron phosphors) were characterized by x-ray diffraction, transmission electron microscope, scanning electron microscopy, selected area electron diffraction, and energy dispersive x-ray spectroscopy. The emission spectra of the samples are unchanged in comparison with that of standard material. The excitation spectra show a redshift in the charge-transfer-state band and a blueshift in the host gap band. In relation to commercial sample, the relative luminescence intensities of nano- and submicron phosphors are increased sufficiently to 64.4% and 93.6%, respectively. Higher quenching concentration of the activator Eu3+ ion was observed in the nanophosphor than that in the phosphor synthesized by solid state reaction. [ABSTRACT FROM AUTHOR]

The poor thermal stability of current commercial white light emitting diodes (WLED) fabricated using a blue chip, a yellow YAG:Ce 3+ phosphor (YAG) and resins, restricts their application in fields where long service time and high power lighting systems are required. Incorporating YAG into glass offers a possible way to resolve the problem by removing the organic resins in LED encapsulation. In the present study, YAG glass-ceramics with bismuth borate glass matrices were prepared using a rapid melt quenching technique. The YAG erosion mechanism was investigated for the first time in various glass matrix compositions at different co-sintering temperatures. The results demonstrate that neither B 2 O 3 nor Bi 2 O 3 individually erodes YAG particles, but the mixtures of B 2 O 3 and Bi 2 O 3 binary glass systems react with YAG and dissolve it almost completely or generate YAl 3 (BO 3 ) 4 (abbreviated as YAB), and they even erode as-produced YAB again under certain conditions. The production of YAB particles increases with the increase of the n Bi /n B ratio at a lower temperature (680 °C), while it first increases and then decreases at a higher temperature (800 °C). The maximum production of YAB can be obtained at the co-sintering temperature of 680 °C with an n Bi /n B ratio of 55:45 or at 760 °C with an n Bi /n B ratio of 35:65. The intermediate Bi 4 B 2 O 9 phase is found during the transformation of YAG into YAB. A simple but efficient approach is proposed to prevent YAG erosion and increase the luminous properties of YAG glass ceramics to a great extent by simply adding Ca 2+ into bismuth borate glass matrices. The degree of YAG erosion decreases with increasing Ca 2+ concentration until an impurity phase appears when the Ca 2+ concentration exceeds 20 mol%. The combination of good white light emission and suitable quantum efficiency as well as higher thermal stability makes the as-prepared YAG glass-ceramics equipped with a blue chip a possible alternative to commercial WLED. [ABSTRACT FROM AUTHOR]

A series of novel Er 3+ doped and Er 3+ /Yb 3+ co-doped Ba 3 Lu 4 O 9 phosphors were synthesized by a simple high-temperature solid-state reaction method. The crystal structure and morphology of the samples were identified by XRD and SEM analysis. Under 980 nm laser diode excitation, the green (at 537 nm and 560 nm) and red (at 660 nm) UC emission were observed, which could be attributed to the ( 2 H 11/2 , 4 S 3/2 )→ 4 I 15/2 and 4 F 9/2 → 4 I 15/2 transitions, respectively. The UC luminescence can be finely tuned from green to dark-yellow light to some extent by increasing Yb 3+ doping concentration. The sintering temperature and doping concentration of Ba 3 Lu 4- x - y O 9 : x Er 3+ , y Yb 3+ were optimized to x = 0.1 and y = 0.6 at 1550 °C. The emission intensity ratio of Green/Red keeps declining monotonically with increasing Er 3+ or Yb 3+ concentration, which is due to the cross-relaxation effect and cooperative energy transfer between the two neighboring Er 3+ ions-as well as back energy transfer from Er 3+ to Yb 3+ ions. Based on the pump-power dependence and UC luminescence decay curves, the energy level diagram and the possible energy transfer mechanism of Er 3+ doped as well as Er 3+ /Yb 3+ co-doped system were investigated in detail. In addition, according to the energy gap law, the possibilities of non-radiative transition between parts of energy levels of Er 3+ ions were calculated. [ABSTRACT FROM AUTHOR]

Bi 3+ , P O 4 3 − and B O 3 3 − doped Sc 0.73 Y 0.2 VO 4 : Eu 0 . 07 3 + phosphors were synthesized by solid state reaction at 1200 °C. The structure, morphology and luminescence properties were investigated. The synthesized phosphors show narrow particle distribution with average size around 2 μm. Under 365 nm excitation, integrate emission intensity increases after doping with Bi 3+ , P O 4 3 − and BO 3 3 − . The optimal doping concentrations are 1%, 20%, 10% for Bi 3+ , P O 4 3 − and BO 3 3 − , respectively. The thermal stability is greatly improved, especially for BO 3 3 − doped sample, whose intensity is about 92% of its original intensity even at 200 °C. [ABSTRACT FROM AUTHOR]

Cr3+‐activated near‐infrared (NIR) phosphors have gained extensive attention for use in NIR phosphor‐converted light‐emitting diodes (pc‐LEDs), which are required for smart NIR spectroscopy techniques. Nevertheless, obtaining broadband NIR‐emitting phosphors with outstanding thermal stabilities and photoluminescence (PL) efficiencies remains a significant challenge. Herein, considering NaSr2XGe5O14 (X = Al, Ga, Sc, and In) as hosts, which possess a large band gap and multiple sites for the substitution of Cr3+ ions. NaSr2XGe5O14:Cr3+ phosphors are successfully prepared using a solid‐state reaction technology. Upon blue light excitation, the phosphors cover a broad NIR emission band in 650–1100 nm region. Notably, an abnormal blueshift and PL enhancement are observed following the substitution of Al/Ga with Sc/In. In particular, the PL internal quantum efficiency is improved from 34.5% (NaSr2GaGe5O14: Cr3+) to 87.5% (NaSr2ScGe5O14: Cr3+). Moreover, the manufactured NIR pc‐LED exhibited an exceptional photoelectric efficiency of 17.7% with an NIR output power of 10.2 mW at 20 mA, and its potential application in nondestructive detection is demonstrated. [ABSTRACT FROM AUTHOR]

Sunlight-like full-spectrum phosphor-converted light-emitting diodes (pc-LEDs) require near-infrared (NIR) emission bands to fill the spectrum gap and consequently propel their widespread applications. Although fluoride NIR phosphors have been increasingly investigated, balancing high quantum efficiency (QE), high thermal stability, and wideband NIR emission to obtain excellent overall performance in a single system is still a challenge for Cr3+-doped fluoride NIR phosphor and is significant for direct utilization. Herein, a high-efficiency and thermally stable broadband NIR emission was realized in a novel LiSrGaF6:Cr3+ fluoride phosphor benefitting from a relatively weak crystal field and electron–phonon coupling effect. Upon blue light excitation, the ultra-broad NIR luminescence ranging from 650 to 1150 nm can be achieved with an FWHM of 149 nm peaking at ∼813 nm. Furthermore, this system possesses a high QE of up to 76.88% and its emission intensity at 423 K still maintains 61.62% of its initial intensity at room temperature. An NIR output power of 42.82 mW and photoelectric conversion efficiency of 14.27% of NIR pc-LED devices have also been presented based on this NIR phosphor, demonstrating its possible application in compact nonvisible light sources. In addition, a highly continuous sunlight-like vis-NIR pc-LED was further constructed by employing a blue chip with commercial cyan (BaSi2O2N2:Eu2+), yellow (Y3Al5O12:Ce3+), red (CaAlSiN3:Eu2+), and this LiSrGaF6:Cr3+ NIR phosphor. The as-obtained pc-LED exhibits an ultra-broad spectrum ranging from 400 nm to 1000 nm, exhibiting a higher color reproduction with a color rendering index (CRI) of 95.1 and luminous efficiency (LE) of 50.22 lm W−1. These results indicate that LiSrGaF6:Cr3+ phosphor can be a promising NIR phosphor candidate for high-quality sunlight-like full-spectrum lighting and infrared night vision technology. [ABSTRACT FROM AUTHOR]

Current white light emitting diodes (WLEDs) have poor thermal stability and lack red‐light, which restrict their applications in high‐power and high‐color‐rendering‐index solid‐state lighting. YAG glass‐ceramics provide an efficient way to resolve these problems. Herein, novel YAG‐embedded calcium bismuth borate glass‐ceramics (YAG‐GCs) with Eu3+ doping were prepared using a rapid melt quenching technique. The precursor glass exhibits superior YAG refractive index matching and high transmittance. Differential scanning calorimeter simulations verify YAG particles react with the precursor glass. The degree of YAG erosion is slight but monotonously increases with the co‐sintering temperature from 640 to 700°C. The erosion products probably contain YAB (Al3Y(BO3)4), Al3Eu(BO3)4, Bi24B2O39, and Ca12Al14O33 phases, and the Bi ion valence state is maintained during the reaction process. The energy transfer from Ce3+ to Eu3+ is suppressed. The YAG‐GC PL intensities monotonously increase as the co‐sintering temperature decrease from 640 to 700°C and the YAG content increase from 2.5 to 7 wt.%. The optical parameters of a WLEDs packed by YAG‐GCs and blue chips are a luminous efficiency of 105.3 lm/W, correlated color temperature of 3940 K and color rendering index of 70.1. The as‐prepared YAG‐GCs are promising candidates for high‐power, warm WLEDs due to their superior thermal stability, high quantum efficiency, and low cost. [ABSTRACT FROM AUTHOR]

BaLu 1.94 Al 4 SiO 12 :0.06Ce 3+ (BLASO:0.06Ce 3+ ) green-emitting phosphor could be easily obtained by a conventional solid-state reaction method at 1400 °C. BLASO:0.06Ce 3+ possesses the garnet structure ( Ia 3 ̅ d space group) with the lattice parameter a = 11.9222(0) Å. The emission peak of BLASO:0.06Ce 3+ is located at 513 nm and its photoluminescent quantum yield is determined to be 92.4% at 25 °C when excited at 450 nm. BLASO:0.06Ce 3+ presents excellent thermal properties, with the photoluminescence intensity at 200 °C only decreased to 91.5% of its room temperature value. A phosphor-converted white LED device fabricated by using BLASO:0.06Ce 3+ as the green phosphor exhibits good optical performance with Ra = 88.5, CCT = 3562 K and CIE1931 chromaticity coordinates as (x = 0.4041, y = 0.3951). The results indicate that BLASO:0.06Ce 3+ phosphor has strong potential applications in developing high color rendering, thermally stable, warm-white LEDs. [ABSTRACT FROM AUTHOR]

The Cr3+-doped near-infrared (NIR) phosphors have been extensively investigated owing to their promising applications in biomedicine, food safety detection, and night vision surveillance. However, achieving broadband (FWHM > 160 nm) NIR emission is still challenging. In this paper, novel Y2Mg2Ga2−xSi2O12:xCr3+ (YMGS:xCr3+, x = 0.005–0.08) phosphors were prepared by a high-temperature solid-state reaction. The crystal structure, photoluminescence properties of the phosphor, and the device performance of a pc-LED were researched in detail. When excited at 440 nm, the YMGS:0.04Cr3+ phosphor exhibited broadband emission in the range of 650–1000 nm, peaking at 790 nm with a full width at half-maximum (FWHM) of up to 180 nm. The wide FWHM of YMGS:Cr3+ is conducive to its extensive application in NIR spectroscopic technology. In addition, the YMGS:0.04Cr3+ phosphor could maintain 70% of the initial emission intensity at 373 K. By combining the commercial blue chip with the YMGS:0.04Cr3+ phosphor, the resulting NIR pc-LED demonstrated a near-infrared output power of 14 mW with a photoelectric conversion efficiency of 5% at a drive current of 100 mA. This work provides a broadband emission NIR phosphor option for NIR pc-LED devices. [ABSTRACT FROM AUTHOR]

For high-efficiency lighting and wide color gamut backlight display, high-quality narrow-band red phosphors for WLEDs are still in high demand. Herein, a novel red-emitting fluoride phosphor Cs2NaGaF6:Mn4+ was successfully synthesized by a simple two-step co-precipitation method and exhibits ultra-intense zero-phonon lines (ZPLs) and long wavelength phonon sidebands under 468 nm blue light irradiation. The ZPL emission peak of Cs2NaGaF6:Mn4+ was located at 627 nm, which is much stronger than its υ6 vibration peak, more matchable with the eye-sensitive region of humans, and beneficial for obtaining higher luminous efficiency of WLEDs. Interestingly, the υ6 vibration peak of this red phosphor is at 636.5 nm, which is larger than that of the common fluoride phosphor A2BF6:Mn4+ (usually at about 630 nm, represented by K2SiF6:Mn4+) at about 6.5 nm. Thanks to the longer wavelength of the υ6 vibration peak, the chromaticity coordinates (0.7026, 0.2910) with a larger x-coordinate value were realized, leading to a potentially wider color gamut of WLEDs. In addition, this phosphor has high thermal stability and its emission intensity at 423 K remains 93.7% of the initial intensity at room temperature. The lumen efficiency of WLED1 packaged with a mixture of Cs2NaGaF6:Mn4+ and YAG:Ce3+ on the InGaN blue chip is 115.7 lm W−1 with the color temperature (Tc) = 3390 K and the colour rendering index (Ra) = 92.5 under 20 mA driving current. The chromaticity coordinates of WLED2 packaged with Cs2NaGaF6:Mn4+ and β-SiAlON:Eu2+ on the InGaN blue chip are (0.3149, 0.3262) and the calculated color gamut is up to 118.4% (NTSC). These results indicate that Cs2NaGaF6:Mn4+ red phosphors have promising applications in the high-quality lighting and display fields. [ABSTRACT FROM AUTHOR]

Phosphor-converted light-emitting diodes (pc-LEDs) have important applications in security surveillance and food testing. However, developing new broadband near-infrared phosphors remains an important issue. Herein, the high-temperature solid-state reaction method was applied to synthesize a new type of Cr3+ doped Mg2Al4Si5O18 broadband NIR phosphor which matches a blue LED chip. It exhibits a broadband near-infrared (NIR) phosphor emission with a focus of 856 nm and a full width at half maximum >200 nm after excitation at 453 nm. The optimum concentration of Cr3+ was established to contain 2 mol%. At 398 K, the luminescence intensity is 45.2% of that at 298 K. The power output of NIR pc-LEDs fabricated by incorporating a 450 nm chip and the Mg2Al4Si5O18:0.02 Cr3+ phosphor is 19.69 mW at 300 mA current. Finally, the developed NIR pc-LED shows significant potential for use in night-vision imaging. [ABSTRACT FROM AUTHOR]

Enhancing the moisture resistance of Mn4+-doped fluoride phosphors is crucial for solid-state lighting (SSL) and liquid crystal display (LCD). Herein, the deteriorated K2AF6:Mn4+ (A = Ti, Si) phosphors were restored with Na2SO3 alkaline reductant, and optimal treatment conditions were systematically determined. The kinetic process for luminescence degradation and restoration, as well as the corresponding reparation mechanism were investigated in detail. These results showed that SO32− anion can reduce Mn4+ to Mn2+, rapidly remove the dark-brown layer of the degradation product, and restore the luminescence intensity of K2AF6:Mn4+ to more than 95%. Therefore, the restored K2TiF6: Mn4+ and K2SiF6: Mn4+ samples exhibit excellent moisture resistance, maintaining to be 66 and 76% of the initial intensity after immersing in deionized water for 300 min. Furthermore, fabricated white light-emitting device using the restored K2TiF6: Mn4+ phosphor also possess color rendering index of 94.2 and correlated color temperature of 3270 K. Our results provide a feasible strategy to significantly improve the moisture resistance of fluoride phosphors, demonstrating a great promise in phosphor-converted white-LED toward lighting and display field. [ABSTRACT FROM AUTHOR]

Full-spectrum lighting has become the development direction for human-centric illumination. However, the reabsorption effect caused by cyan, green and yellow multiple-phosphor packaging leads to low luminous efficiency. In this work, a broadband cyan-green phosphor is proposed to replace the cyan and yellow phosphors for highly efficient and thermally robust full-spectrum WLEDs. A new family of oxyfluoride garnet phosphors Lu 2 QMg 2 Al 3 O 9 F 3 : Ce3+ (Q = Ca, Sr, Ba) has been developed by incorporating F- into the classic LuAG: Ce3+ green phosphor. The excess charge was compensated by substituting trivalent Lu3+ and Al3+ with divalent alkaline earth element. The low covalency and phonon energy of fluorine-containing system endow these serial phosphors with efficient and thermally stable blue-shifted emission. The representative Lu 2 SrMg 2 Al 3 O 9 F 3 : Ce3+ exhibits a broadband cyan-green emission peaked at 513 nm with a 105 nm FWHM. Furthermore, outstanding quantum efficiency (88.4%) and thermal stability (94.3% @ 423 K) were achieved. This oxyfluoride phosphor was packaged with red phosphor without cyan phosphor on a blue chip. The obtained WLEDs show an excellent color rendering index (R a = 96.8) with luminous efficiency (LE = 106 lm/W). This research might pave a promising avenue for the development of next-generation full-spectrum lighting. • A new family of oxyfluoride garnet cyan-green phosphors was obtained. • The F- incorporation endows the phosphors with efficient and thermally stable blue-shifted emission. • The Lu 2 SrMg 2 Al 3 O 9 F 3 : Ce3+ exhibits a 513 nm centered emission with a 105 nm FWHM. • Ra=96.8 and LE=106 lm/W were achieved by replacing the cyan and yellow phosphor. [ABSTRACT FROM AUTHOR]

• ScP 3 O 9 : Cr3+, shows a broadband NIR emission and peaking at ∼900 nm. • The PL intensity of ScP 3 O 9 : Cr3+ can be enhanced by phase transition. • ScP 3 O 9 : Cr3+, Nd3+, Pr3+ exhibits an excellent PL thermal stability (86 % at 423 K). • The NIR pc-LED device can be applied in non-destructive analysis. Near-infrared (NIR) phosphors play an important role in NIR pc-LEDs. However, NIR phosphor with long wavelength are still suffered from low efficiency and poor thermal stability. Herein, a blue light excitable ScP 3 O 9 : Cr3+ NIR phosphor with an emission peak > 880 nm is reported. Significantly, the PL intensity of ScP 3 O 9 : Cr3+ increased to 241 % when the monoclinic phase changes to cubic. Moreover, by co-doping the cubic ScP 3 O 9 : Cr3+ with Nd3+, Pr3+ ions, the PL internal quantum efficiency (IQE) of the phosphors increased from 62 % to 74 %, and the thermal quenching of the phosphor is suppressed effectively (86 % at 423 K). The energy transfer processes between Cr3+ and Nd3+, Pr3+ ions are proposed to be responsible for the enhancement. Furthermore, an efficient NIR pc-LED was fabricated, and gives a high photoelectric efficiency of 16.5 % (26.8 mW at 60 mA). Finally, multifunctional applications of the NIR device in night-vision and nondestructive analysis were demonstrated. An efficient broadband NIR phosphor ScP 3 O 9 : Cr3+, Nd3+, Pr3+ with excellent thermal stability is prepared to fabricate compact NIR pc-LED based on commercial blue diode chips. The NIR pc-LED device is promising for the applications in non-destructive analysis. [Display omitted] [ABSTRACT FROM AUTHOR]

Compared with oxide-based NIR phosphors, fluoride phosphors have received great attention recently due to their good thermal resistance and high photoelectric efficiency. In this work, novel LiBAlF 6 :Cr3+ (B = Ca, Sr) with low phonon energy and relatively weak electron-phonon coupling were synthesized through a facile hydrothermal approach. Benefiting from low Dq/B, an ultra-broad NIR emission extending from 650 nm to 1100 nm can be achieved in these phosphors under excitation of blue light. Among them, LiSrAlF 6 :Cr3+ presents a FWHM of 155 nm. At 423 K, LiCaAl 0.4 F 6 : 0.6Cr3+ and LiSrAl 0.4 F 6 : 0.6Cr3+ maintain 66.63% and 55.47% of their initial intensities, respectively. Better thermal stability of LiCaAlF 6 : Cr3+ could be attributed to the broad band gap and weak electron-phonon coupling effect. Photoelectric conversion efficiencies of 5.002% and 5.468% at 300 mA could be obtained for NIR pc-LEDs packaged with LiCaAl 0.4 F 6 : 0.6Cr3+ and LiSrAl 0.4 F 6 : 0.6Cr3+, respectively. A slightly internal bruise inside apple and water level behind trademark in bottle could be clearly detected, revealing that LiBAlF 6 :Cr3+ (B = Ca, Sr) phosphors have great application potential in infrared inspection. [ABSTRACT FROM AUTHOR]

• A novel red phosphor Ca 9 Nd(PO 4) 7 :Eu3+ was synthesized for the first time. • The occupation and crystalline structure of Ca 9 Nd(PO 4) 7 :xEu3+phosphors were thoroughly determined by DFF simulation and Rietveld refinement. • This phosphor can be efficiently excited by near-ultraviolet light to present intense red light emission. • The phosphor exhibits good property of thermal stability. • The WLED fabricated with Ca 9 Nd(PO 4) 7 :xEu3+ has shown superb color temperature and color purity. A series of Ca 9 Nd(PO 4) 7 :xEu3+ (abbreviates as CNP:xEu3+, where x varies from 0.1 to 0.5) phosphors were prepared via conventional solid-state reaction. The X-ray diffraction (XRD) data and Rietveld refinement suggested a successful preparation of CNP:xEu3+ with no sign of impurities. The structure of CNP:Eu3+ belongs to a trigonal crystal system the same as that of β-Ca 3 (PO 4) 2. Thus, Eu3+ ions should theoretically occupy the Ca sites in CNP. All CNP:xEu3+ phosphors showed red emission under excitation in the near-ultraviolet (n-UV) range. The optimal dosage with the best luminescent performance was found at x = 0.3 with critical interaction radius (Rc) of 15.57 Å. The electric dipole-dipole interaction was suggested to be the reason that leads to concentration quenching. The relative luminous intensity of CNP:0.3Eu3+ phosphor at 373 K can remain 70.4% of the initial value at room temperature (RT). The color purity of CNP:0.3Eu3+ phosphor is 92.8%, which is much higher than many other red phosphors. A white light emitting diode (WLED) fabricated with CNP:Eu3+ exhibited correlated color temperature (CCT) of 4602 K and a high Ra of 74.7. The above results illustrate that Ca 9 Nd(PO 4) 7 :Eu3+ could serve as a promising red phosphor for n-UV WLEDs. [Display omitted] [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) phosphor-converted light emitting diode (pc-LED) light sources have broad application prospects in environmental science, biomedical and plant growth fields. However, NIR phosphors still suffer from narrowband emission and low thermal stability. Here, we prepared a novel Lu2CaMg2−xSi3O12:xCr3+ (LCMS:xCr3+, x = 0.005–0.06) phosphor with broadband emission by a high-temperature solid state reaction. Under excitation at 450 nm, the emission spectrum of the LCMS:0.05Cr3+ phosphor shows a broadband emission in the range of 650–1000 nm with a large full width at half maximum (FWHM) of 125 nm and an R-line emission of 692 nm. In addition, the LCMS:0.05Cr3+ phosphor has good thermal stability and can maintain 70% emission intensity at 150 °C relative to that at room temperature. The LCMS:0.05Cr3+ phosphor exhibits a high internal quantum efficiency (IQE) of ∼76%. Using this phosphor, a NIR pc-LED with photoelectric efficiencies of 14.8% at 100 mA and 6.0% at 320 mA and NIR output powers of 59.5 mW at 100 mA and 181.0 mW at 320 mA was obtained. The broadband LCMS:0.05Cr3+ phosphor with a NIR emission peaked at 750 nm can serve as a light source for plant cultivation and has superior application prospects in the agriculture field. [ABSTRACT FROM AUTHOR]

Eu2+-activated BaSi 2 O 2 N 2 oxonitridosilicate phosphor is an efficient cyan compensator to improve the color rendering index of WLEDs for full-spectrum lighting. However, the low luminescent efficiency and poor thermal stability of this type of phosphor severely restrict its practical industry applications. Herein, SiC was proposed into the preparation process of BaSi 2 O 2 N 2 to enhance the luminescence and thermal stability. Due to the very small amount of SiC addition, the samples of BaSi 2 O 2 N 2-4x/3 C x :Eu2+ maintain the orthorhombic crystal structure of BaSi 2 O 2 N 2 :Eu2+, but the unit cell volumes and particle sizes become larger. The luminescent intensity reaches the maximum when x = 0.075 and the absorption efficiency and internal quantum efficiency are 67.59% and 58.26%, which are increased by 5.34% and 14.66% relative to the SiC-free sample, respectively. The bandgap and lifetime of Ba 0.97 Si 2 O 2 N 1.9 C 0.075 :0.03Eu2+ are calculated to be 2.06 eV and 407.91 ns, respectively. The sample of Ba 0.97 Si 2 O 2 N 1.9 C 0.075 :0.03Eu2+ possesses a higher activation energy of 0.383 eV and exhibits a little loss of 13.3% of luminescence intensity at 423 K, which is improved by 11.4% relative to the SiC-free sample. Higher structural stiffness derived from the partially replacement of Si−N bonds by Si-C is supposed as the main reason of the higher thermal stability. The luminescence of Ba 0.97 Si 2 O 2 N 1.9 C 0.075 :0.03Eu2+ degrades only by 4.64% in five thermal cycles, which mainly thanks to the improved antioxidant of Eu2+. The Ba 0.97 Si 2 O 2 N 1.9 C 0.075 :0.03Eu2+ sample demonstrates an excellent color stability with a tiny chromaticity shift of ~28.19 × 10-3 ranging from 298 to 423 K. A WLED with the cyan-emitting Ba 0.97 Si 2 O 2 N 1.9 C 0.075 :0.03Eu2+ exhibits a full spectrum with CRI of 95.1. [ABSTRACT FROM AUTHOR]

Fluoride phosphors as red components for warm white LEDs have attracted a tremendous amount of research attention. But these phosphors are extremely sensitive to moisture, which seriously limits their practical industrial applications. To tackle this problem, unlike all the straightforward preventive strategies, a reverse strategy "Good comes from bad" was successfully developed to treat the degraded K2SiF6 : Mn4+ (D‐KSFM) phosphor in the present study, which not only completely restores the luminescence properties, but also significantly enhances the moisture resistance at the same time. After treatment with an oxalic acid solution as restoration modifier, the emission intensity of the D‐KSFM phosphor can be restored to 103.7% of the original K2SiF6 : Mn4+ red phosphor (O‐KSFM), and the moisture resistance is remarkably improved. The restored K2SiF6 : Mn4+ (R‐KSFM) maintains approximately 62.3% of its initial relative emission intensity after immersing in deionized water for 300 min, while the reference commercial K2SiF6 : Mn4+ with a protective coating (C‐KSFM) is only 33.2%. As a proof of general applicability, this strategy was also conducted to K2TiF6 : Mn4+ phosphor, which is less moisture‐stable than K2SiF6 : Mn4+. The luminescence intensity of the degraded K2TiF6 : Mn4+ (D‐KTFM) phosphor can be restored to 162.6% of original level of the K2TiF6 : Mn4+ synthesized through a cation exchange approach without any treatment (O‐KTFM). The emission intensity of the restored K2TiF6 : Mn4+ (R‐KTFM) phosphor retains 62.8% of its initial emission intensity after soaking in deionized water for 300 min. Finally, the R‐KSFM phosphors were packaged into white light‐emitting diodes with blue InGaN chips and Y3Al5O12 : Ce3+ yellow phosphors. The WLEDs display excellent color rendition with higher color rendering index, lower color temperature (WLED‐II: Ra=83.6, R9=57.3, 3743 K, ηl=199.68 lm/W; WLED‐III: Ra=90.4, R9=94.2, 2892 K, ηl=183.3 1 m/W). The above results show that the reverse strategy can be applied in those phosphor materials with poor moisture resistance to restore luminescence properties and improve moisture resistance without excessively care about the deterioration during the production, storage and transportation. [ABSTRACT FROM AUTHOR]

Y1.94MAl4SiO12:0.06Ce3+ (M = Ba, Sr, Ca, Mg) phosphors were successfully prepared through a classic solid‐state reaction method. The crystal structures, photoluminescence spectra, quantum yields, and thermal stabilities of the phosphors were investigated in detail. The results indicate that all Y1.94MAl4SiO12:0.06Ce3+ phosphors maintain the crystal structure of garnets. The emission peaks of Y1.94MAl4SiO12:0.06Ce3+ (M = Ba, Sr, Ca, Mg) phosphors are located at 537, 538, 554, and 565 nm, respectively. A red‐shift trend of emission peak is observed with decreasing M radius, which can be ascribed to the increase in the crystal‐field splitting in the Ce3+ 5d level owing to the co‐doping of M2+−Si4+. Under 460 nm excitation, the luminescence quantum yields and thermal stabilities of the Y1.94MAl4SiO12:0.06Ce3+ phosphors decreased with the decrease of M radius. The IQE of the Y1.94BaAl4SiO12:0.06Ce3+ phosphor is 92.89%, and the resistance to thermal quenching is improved to be 93.32% at 150°C. In addition, the color shifts of Y1.94MAl4SiO12: 0.06Ce3+ phosphors with increasing temperature are all tiny, which also demonstrates good resistance to thermal quenching of luminescence. The linear shrinkage of Y1.94MAl4SiO12:0.06Ce3+ phosphors is significantly improved compared with that of YAG: Ce3+, which is expected to generate Y1.94MAl4SiO12:0.06Ce3+ transparent/translucent ceramics and fabricate high‐powder w‐LEDs for high‐quality solid‐state lighting in the future. [ABSTRACT FROM AUTHOR]

An oxyfluoride red phosphor Cs2MoO2F4:Mn4+ was synthesized via a facile co-precipitation route with a certain molecular ratio of CsF and MoO3. X-ray diffraction analysis and its Rietveld refinement reveal that Cs2MoO2F4:Mn4+ crystallized in an orthorhombic structure with the Amam (63) space group. Upon blue light excitation, Cs2MoO2F4:Mn4+ exhibits a series of sharp red emission lines around ∼634 nm and the zero-phonon line (ZPL) is visible at 619 nm. The optimal doping amount of Mn4+ in Cs2MoO2F4 is 1.12%, and the decay curves show a good fit with the single exponential decay model. The fluorescence lifetime of the synthesized phosphors is relatively short and calculated as 3.18 to 2.46 ms, the Mn4+ ions in Cs2MoO2F4 experience a strong crystal field strength with a Dq/B of ∼4.87, and the distinct nephelauxetic ratio β1 is determined to be ∼1.0226. The thermal quenching mechanism of Mn4+ was also studied. Furthermore, by using the as-synthesized Cs2MoO2F4:Mn4+ phosphor as a red component and β-SiALON as a green light component, a WLED was fabricated with a high luminous efficacy of 114.70 lm·W−1 and wide color gamut of 109.1% of the National Television Standard Committee (NTSC) value. Hence, the Cs2MoO2F4:Mn4+ phosphor with a short fluorescence lifetime could potentially be an efficient red compensator for application in rapid-response backlight displays. [ABSTRACT FROM AUTHOR]

A novel Sr2MgB2O6 (SMBO) green-emitting phosphor co-doped with Ce3+–Tb3+ was synthesized at 950 °C via solid-state reactions, and the ultra-narrow-band green emission of Tb3+ was significantly enhanced almost 20 times via energy transfer from Ce3+ to Tb3+. It was found to have a broad excitation band (250 to 400 nm), and the full width at half-maximum (FWHM) of the dominant green emission band around 544 nm was only about 10 nm. The electronic band gap of the SMBO matrix was calculated by density functional theory (DFT) to be 4.60 eV, and this was well verified by the diffuse reflection spectra results. Furthermore, the composition-optimized phosphor SMBO:0.05Ce3+,0.05Tb3+ exhibits excellent thermal quenching resistance (75.3% intensity at 423 K) and relatively high external quantum efficiency (EQE = 48.92%). Finally, two white light-emitting diode (WLED) packages were fabricated via combining a 365 nm n-UV chip, the optimal sample and commercial blue and red phosphors to assess the application potential of the phosphors. The test results indicate that the obtained WLEDs-1 fabricated with K2SiF6:Mn4+ has an outstanding color rendering index (Ra = 85.7) and Commission Internationale de L'Eclairage (CIE) coordinates (0.3242, 0.3334). Meanwhile, the color gamut can reach 87% of the National Television Standards Committee (NTSC) CIE 1931 color gamut. WLEDs-2 fabricated with red emitting CaAlSiN3:Eu2+ produced warm white light with color coordinates of (0.3792, 0.3810), a high color rendering index of 82.3, and a low correlated color temperature of 4065 K. These results reveal the broad prospects of this phosphor for LED-based applications. [ABSTRACT FROM AUTHOR]

A narrow-band green-emitting phosphor ZnB2O4:Mn2+, Mg2+ was prepared by solid-state reactions. X-ray diffraction (XRD) and the Rietveld structural refinements were performed. The results show that the introduction of Mg2+ may suppress the formation of an impurity phase. The micro-structure, photoluminescence (PL) and reflectance spectra, PL decay curves as well as thermal quenching behavior were investigated. The phosphors exhibit a broad absorption band from 200 to 510 nm, while the emission spectra show a narrow band centered at 538 nm with a full-width at half-maximum (FWHM) of about 34 nm. Furthermore, after the introduction of Mg2+, the luminescence intensity of phosphor ZnB2O4:0.07Mn2+, 0.10Mg2+ is significantly enhanced by about 2 times, and it presents a relatively low thermal quenching behavior. The corresponding mechanisms for performance improvement were investigated in detail and the ion-size compensation effect of Mg2+ to Mn2+ is proposed. Additionally, the high activation energy (0.202 eV) and ultra-high color purity (97%) were calculated. These results imply that the ZnB2O4:Mn2+, Mg2+ phosphor has broad application prospects in the field of advanced backlight display. Moreover, the introduction of Mg2+ may be useful as an effective strategy to enhance the luminescence properties and thermal stability of Mn2+ or even other element-doped phosphors. [ABSTRACT FROM AUTHOR]

Research on near-infrared (NIR) emission of Tm3+ and Yb3+ co-doped upconversion (UC) materials has accepted many interests owing to delightful features for frontier applications. In this work, we focus on the preparation of pure NIR emission and the improvement of absolute sensitivity (S A) on temperature in Tm3+ and Yb3+ co-doped novel double perovskite Gd 2 ZnTiO 6 (GZT) phosphors. Upon 980 nm excitation, these phosphors perform dramatical NIR emissions, and the integral intensity percentage of NIR emission versus total visible emissions reaches up to 99.88%. A high S A value with 1.7351 K−1 at 473 K for the I 801 /I 650 is obtained via introducing excellent NIR emission. Besides, the S A value of non-thermally coupled levels is higher than that of thermally coupled levels. These results suggest that this kind of UC material may be a candidate for NIR imaging and temperature detection applications. Image 1 High sensitivity based on non-thermally coupled levels is received via utilizing intense NIR emission in Tm3+ and Yb3+ co-doped double perovskite GZT phosphors. • Upconversion properties of Tm3+ and Yb3+ co-doped novel double perovskite Gd 2 ZnTiO 6 phosphors are investigated in detail. • Intense and nearly pure NIR emission with high integral intensity percentage that achieves 99.88% is obtained. • High S A with 1.7351 K−1 at 473 K for N-TCLs is received via utilizing intense near-infrared emission. [ABSTRACT FROM AUTHOR]

A series of tunable blue-green emitting phosphors Al 5 O 6 N: Eu2+, Tb3+ were prepared via gas-pressure sintering reaction process. The morphology, UV–Vis reflectance spectra, photoluminescence properties, decay behavior, Eu2+ occupy site, energy transfer mechanism and thermal stability were investigated systematically. The Al 5 O 6 N: 0.003Eu2+, 0.01Tb3+ phosphor exhibits strong green emission under near-UV excitation due to briskly efficient energy transfer from Eu2+ to Tb3+. The maximum energy transfer efficiency calculated by decay lifetime can reach 80%. The mechanism of energy transfer from the Eu2+ to Tb3+ is considered to be a dipole−dipole type. The critical distance of the energy transfer is calculated via the concentration quenching method. Moreover, the color emission from blue to green can be obtained through controlling the concentration of Eu2+ and Tb3+. These results reveal the potential value of Al 5 O 6 N: Eu2+, Tb3+ phosphors as green light emitting material for near-UV pumped white light-emitting diodes. [ABSTRACT FROM AUTHOR]

Energy transfer (ET) and cross-relaxation (CR) processes play significant roles in regulating emitting colors and intensity of upconversion (UC) materials. Calculating the coefficients in ET and CR processes can provide visual descriptions for evaluating the UC luminescence properties. Here, we find that those ET and CR processes are responsible for the color-tunable properties in Gd 2 Ce 2 O 7 : Yb3+, Er3+ phosphors. By solving the rate equation, mathematical expressions are established to calculate the ET and CR coefficients based on the experimental UC spectra and lifetimes. The results are benefit to evaluate the efficiencies of ET and CR processes in quantization in different Yb3+ ion concentrations doped samples. The coefficients of ET process arise from 1.05 to 7.93 × 1017 cm3s−1 while those of CR process increase from 2.69 to 72.01 × 1017 cm3s−1 with increasing the Yb3+ ion concentration, which suggest that the CR and ET processes are efficient in Gd 2 Ce 2 O 7 host. Furthermore, potential temperature sensing properties are also evaluated according to the fluorescence intensity ratio of 2H 11/2 and 4S 3/2 levels and the maximal sensitivity (S) is achieved about 0.00337 K−1 at 503 K. This work provides an insight into the evaluation of those UC processes and reveals the capacity in color-tunable and temperature sensing aspects. [ABSTRACT FROM AUTHOR]

A series of novel green emitting γ -AlON: Mn2+, Mg2+ and γ -AlON: Mn2+, Mg2+, M (M = Li+, Na+, K+, Si4+) phosphors were fabricated with the gas-pressure sintering reaction process. The phase structure, morphology and photoluminescence properties of the phosphors were characterized via X-ray powder diffraction, scanning electron microscopy, and photoluminescence spectroscopy. Meanwhile, the charge compensation methods were utilized to eliminate the disadvantage of charge imbalance between Al3+ and Mn2+. The results show that the luminescence intensity of Mn2+ was maximally enhanced by the introduction of Si4+ ions, which was 2.36 times that of the sample without charge compensator. Moreover, as the temperature reached at 150 °C, thermal stability of the samples contained charge compensator Li+ and Si4+ were improved to 93% and 90% of that the room temperature, respectively, while the original sample was 85%. These luminescence properties were enhanced due to the introduction of charge compensators which reduce defects caused by charge imbalance. In addition, the specific mechanisms were discussed in detail. In general, the charge compensation could be used as an effective strategy to strengthen thermal stability and luminescence performances of phosphors. [ABSTRACT FROM AUTHOR]

Abstract Upconversion (UC) optical thermometers using the fluorescence intensity ratio (FIR) technique arising from the thermally coupled energy levels (TCLs) are still suffering from low sensitivity owing to the restriction of small energy gap. In the present study, a strategy to strive for superior temperature sensitivity and signal discriminability is employed with the help of non-thermally coupled energy levels (NTCLs). A novel tri-doped Ba 3 Y 4 O 9 : Ho3+/Tm3+/Yb3+ phosphor with rhombohedral symmetry was successfully prepared via a solid-state reaction method, and the temperature sensing performance was evaluated by analyzing temperature-dependent upconversion emission spectra. The emission intensities of both Ho3+ and Tm3+ activators can be almost completely restored to their original values when the temperature of the sample is cooled to room temperature. The temperature-dependent FIR between NTCLs can be fitted well by a derived three-term equation with the correlation coefficient above 99.6%, and the FIR of NTCLs exhibits high temperature sensitivity over a wide temperature range owing to the different temperature responses of the NTCLs. The maximum absolute sensitivity S A and relative sensitivity S R values reaches as high as 0.0552 K−1 and 1.49% K−1, respectively, which are much higher than those of the previously reported bulk UC optical temperature sensing materials. Moreover, the emission bands of NTCLs are well separated, which endows the material a good signal discriminability for temperature detection. Excellent temperature sensing performance is also demonstrated in Er3+/Tm3+/Yb3+ tri-doped Ba 3 Y 4 O 9 , evidencing the validity of this strategy. These results indicate that the present UC materials can be potential candidates for optical temperature sensors, and the present strategy will provide a thought for developing other innovative UC temperature sensing materials. [ABSTRACT FROM AUTHOR]

The addition of a red-emitting phosphor to YAG:Ce3+-based white light-emitting diodes (WLEDs) greatly facilitates their applications in the field of high-color-rendering-index warm solid-state lighting. It is highly desirable to develop a red phosphor with satisfactory spectral features and low synthesis cost. In this study, a novel non-rare-earth and nonequivalent doping type of Cs2NbOF5:Mn4+ oxyfluoride red-emitting phosphor with high luminous efficiency was obtained via a facile room-temperature co-precipitation method, and its morphology and luminescent properties were investigated in detail. The Cs2NbOF5:Mn4+ phosphor with micro-rod-like morphology exhibited broad band absorption at blue light region (∼474 nm) and narrow bandwidth emissions at red region (∼633 nm). The color purity of the Cs2NbOF5:Mn4+ phosphor was calculated to be about 99%, and the internal quantum yield (QY) under 474 nm excitation was 63.4%. The concentration quenching of Mn4+ in Cs2NbOF5 matrix was mainly due to dipole–dipole interactions, and the activation energy of temperature quenching was calculated to be ∼0.2610 eV. The demonstration of a blue InGaN LED chip in combination with a blend of newly developed Cs2NbOF5:Mn4+ red phosphor and YAG:Ce3+ yellow phosphor greatly decreased the correlated color temperature (CCT) from 6255 to 3517 K while significantly improving the color rendering index (CRI) from 72.5 to 87.5. It deserves to be mentioned that the brand-new matrix to phosphor in the present study can be extended to various niobium/tantalum oxyfluoride series, which is very helpful for developing and designing new red phosphors. [ABSTRACT FROM AUTHOR]

Abstract Lack of red-light of current w-LEDs restricts their applications in the field of high color rendering index warm solid-state lighting. Fluoride phosphors doped with Mn4+ provide an efficient way to resolve the problem. Unfortunately, these excellent Mn4+ activated fluoride red phosphors are generally synthesized in highly toxic HF solution. In this paper, we report a novel green synthetic route to prepare a non-rare-earth and nonequivalent doping type of K 2 NbF 7 :Mn4+ red phosphor with micro-rod-like morphology. The results of XRD and its Rietveld refinement reveal that all the samples possessed only a single phase with monoclinic P21/c structure and the Mn4+ ions were successfully incorporated into the crystal lattice. The Mn4+ ions in K 2 NbF 7 matrix have a highly distorted octahedral environment, which strengthen the intensity of zero phonon line (ZPL). The strongest absorption and excitation bands appear in blue region of diffuse refection spectra (DRS) and the photoluminescence excitation (PLE) of K 2 NbF 7 :Mn4+ sample, which demonstrates the product perfectly match with the most popular GaN-based blue chip. Under blue light illumination, the as-prepared K 2 NbF 7 :Mn4+ sample exhibits intense sharp-line red fluorescence (∼628 nm) with internal quantum yield (QY) of 71.3%, an extreme narrow full width at half-maximum (FWHM) of ∼2.8 nm, and an ultra-high-color purity of 99.2%. Impressively, by incorporating K 2 NbF 7 :Mn4+ as a red component, a warm w-LED with high CRI of 83.8, low color temperature of 3010 K and high luminous efficiency of 115.91 lm/W is obtained, demonstrating great validity of K 2 NbF 7 :Mn4+ red phosphor for white LED devices. Highlights • The K 2 NbF 7 :Mn4+ red phosphor with high luminous efficiency was obtained successfully via a novel HF-free approach. • Reaction mechanism of K 2 NbF 7 :Mn4+ red phosphor, including incorporation mode of Mn4+ into K 2 NbF 7 host, were investigated carefully. • Optical properties of K 2 NbF 7 :Mn4+ red phosphor, especially the intense ZPL emission, were investigated carefully. • Addition of K 2 NbF 7 :Mn4+ red phosphor, a warm w-LED with high CRIand low color temperature is obtained. [ABSTRACT FROM AUTHOR]

A series of Er3+, Tm3+, Yb3+ co-doped or tri-doped SrLu2O4 phosphors were synthesized by a high-temperature solid-state reaction method. The crystal structure was characterized by X-ray diffraction technique and further validated by Rietveld refinement. The chemical composition and elemental distribution of tri-doped sample were determined by the energy-dispersive spectrometry. It is worthwhile to note that the upconversion (UC) luminescence of as-prepared samples could be precisely controlled by adjusting the Yb3+ doping concentration and the excitation pump power. A bright UC white light in Er3+/Tm3+/Yb3+ tri-doped SrLu2O4 samples was observed by controlling the intensities of red, green and blue emissions. Under various pump powers in the range of 290-810 mW, the color coordinates could be effectively tuned in a quite broad white region. Particularly, the color coordinate of optimal sample under 630 mW at 980-nm excitation is (0.3336, 0.3244), which is very close to the standard white-light illumination (0.333, 0.333) and the corresponding correlated color temperature is 5442 K. Based on the UC emission spectra and luminescence decay curves, the energy transfer (ET) mechanisms involved in the different UC processes were proposed in detail. The results imply that ET processes of Yb3+ → Er3+, Yb3+ → Tm3+ and Tm3+ → Er3+ worked simultaneously in tri-doped system and produced white UC emissions by means of two- or three-photon processes. The Er3+/Tm3+/Yb3+ tri-doped SrLu2O4 phosphor can be a potential candidate for white UC material in displays, backlights and white-light sources. [ABSTRACT FROM AUTHOR]

The investigation on single phase multi-color phosphors is highly meaningful for near-ultraviolet chip based white light emitting diodes. In this work, a series of Eu 2+ and Tb 3+ singly doped and Eu 2+ /Tb 3+ codoped Sr 5 (PO 4 ) 3 Cl phosphors were synthesized via a high-temperature solid state reaction method. The luminescence spectra and decay curves of Eu 2+ and Tb 3+ singly doped samples were discussed, the optimal doping concentrations were determined. Thanks to the spectra overlap between Eu 2+ and Tb 3+ , nonradiative energy transfer from Eu 2+ to Tb 3+ was investigated. It is found electric dipole-dipole interaction played the main role for the energy transfer in codoped samples, the highest energy transfer efficiency was calculated to be 60.98%. Tunable emissions are observed for codoped samples by adjusting doping concentration. The thermal quenching properties were discussed and the activation energy (ΔE) was estimated in the present work. [ABSTRACT FROM AUTHOR]

• A novel thiourea loading strategy was proposed to modify KSF phosphor. • The excellent water resistance was obtained after thiourea treatment. • The degradation and restore mechanisms of T-KSF phosphor was revealed. Recently, Mn4+ doped fluoride phosphors have been considered as ideal candidate materials employed in white light-emitting diodes (WLEDs). However, the extremely serious performance deterioration in a wet environment has affected their practical commercial applications. Herein, we developed a novel thiourea loading strategy for greatly improving the moisture resistance of typical K 2 SiF 6 : Mn4+ (KSF) red phosphors through treated by thiourea ethanol solution evaporation. The luminescent properties and moisture resistance have been discussed in detail, and the underlying moisture resistance mechanism was further proposed. The results show that the moisture resistance of KSF phosphor treated by thiourea significantly increased approximately sevenfold than that of untreated counterpart, exhibiting a potential application in the WLEDs backlight with high gamut display. These works brings up a promising alternative strategy for enhancing moisture resistance and provides a deeper understanding on the performance degradation mechanism for a variety of Mn4+ doped fluoride phosphors system. [Display omitted] [ABSTRACT FROM AUTHOR]

The far-red light with peak wavelength around 730 nm plays an important role in plant growth. However, there are few emission spectra of Mn4+-doped oxide phosphors that could match with the absorption spectrum of phytochromes Pfr. In this study, a series of Mn4+-activated SrLa 2 Al 2 O 7 phosphors was successfully synthesized by the method of high-temperature solid-state reaction. The structure of Mn4+-activated SrLa 2 Al 2 O 7 was characterized and photoluminescent properties, thermal stability, luminescence lifetime, and internal quantum efficiency (IQE) were measured. The SrLa 2 Al 2 O 7 phase structure belongs to I4/mmm (139) space group with a tetragonal system. Under 365 nm excitation, far-red emission spectra of SrLa 2 Al 2 O 7 :Mn4+ phosphors range from 650 nm to 800 nm with a peak at 731 nm, which matches well with the absorption band of the phytochrome Pfr. The crystal field strength D q /B of Mn4+ ions in SrLa 2 Al 2 O 7 matrix is 2.79. The optical band gaps are 5.04 eV for SrLa 2 Al 2 O 7. The integrated emission intensity of SrLa 2 Al 1·994 O 7 :0.006Mn4+ phosphors at 373 K remains 43% of that at room temperature, and the luminescence lifetime is 1.99 ms. Finally, the as-prepared SrLa 2 Al 1·994 O 7 :0.006Mn4+ phosphors were mounted on a 365 nm NUV chip to fabricate far-red emitting LED devices. The observed emission spectra were confirmed to match well with the spectra of phytochrome Pfr, which implies that SrLa 2 Al 2 O 7 :Mn4+ phosphors have potential applications in the field of plant growth illumination. • Mn4+-activated SrLa 2 Al 2 O 7 phosphors were successfully synthesized. • PL spectra match well with the absorption band of Pfr. • The excitation peak matches nicely with the 365 nm chip. [ABSTRACT FROM AUTHOR]

A series of Ba 3 Sc 4 O 9 :Ho 3+ /Yb 3+ phosphors were synthesized by a high-temperature solid-state reaction method. The phase purity and upconversion luminescence were characterized by X-ray diffraction and photoluminescence spectroscopy. The sintering temperature and doping concentrations were optimized to obtain the strongest emission intensity. Under 980 nm laser diode excitation, the green (545 nm, 5 F 4 / 5 S 2 → 5 I 8 ) and red (665 nm, 5 F 5 → 5 I 8 ) emissions were observed. The cross-relaxation and back-energy-transfer processes play an important role to adjust the emission intensity ratio of Green/Red at different dopant concentrations. Based on the energy level diagrams, the energy transfer mechanisms are investigated in detail according to the analysis of pump power dependence and luminescence decay curves. The upconversion luminescence properties of the phosphor were evaluated and the results show good color monochromaticity and relatively high upconversion luminescence intensity. The Ba 3 Sc 4 O 9 :Ho 3+ /Yb 3+ can be a good candidate for green upconversion material in display fields and fluorescent labeling. [ABSTRACT FROM AUTHOR]

Near-infrared phosphor-converted light emitting diodes (NIR pc-LEDs) is developing rapidly in plant cultivation because of its low cost, compact size and high efficiency. The NIR light of 700 ∼ 760 nm is known to be beneficial for seed germination and growth. Therefore, the exploration of NIR phosphors with specific wavelength and high efficiency is essential for the development of high-performance plant cultivation pc-LEDs. In this study, a highly efficient and thermal stable Cr3+ doped Lu 2 CaAl 4 SiO 12 (LCAS) phosphor with broadband NIR emission covering phytochrome P fr absorption range was successfully realized via Ca2+-Si4+ co-substitution of Lu3+-Al3+ pairs. The LCAS:0.07 Cr3+ exhibits a major emission peak of 740 nm with a FWHM of 160 nm and its internal/external quantum yield (IQY/EQY) is as high as 80%/30.5%. The integrated emission intensity of LCAS:0.07Cr3+ at 423 K lost only 33.8% of its initial intensity, indicating that it has a good thermal stability. When the LCAS:0.07Cr3+ was packaged into a pc-LED with a driving current of 320 mA, the device output power and photoelectric efficiency reached 90.6 mW and 8.6%, respectively, demonstrating that this phosphor has potential application in plant cultivation lighting. • A NIR phosphor LCAS: Cr3+ was successfully prepared. • The emission spectrum of LCAS: Cr3+ fits well with the absorption band of P fr. • The NIR phosphor exhibits relatively high IQE/EQE. [ABSTRACT FROM AUTHOR]

Due to Eu2+ and Eu3+ ions often co-exist in the crystal lattices, the luminous intensity of some phosphors is limited greatly. In this work, we propose a crystal-site engineering approach to reduce Eu3+ to Eu2+ in the KBaYSi 2 O 7 lattice through substitution of Ba2+ by Ca2+ or Sr2+. The mechanism between the local environmental regulation of the crystal structure around Eu2+ as well as the luminous intensity and thermal stability of the phosphor was systematically explored. The results of XRD, Rietveld refinement and EDX confirmed that Ca2+ and Sr2+ are dissolved into the crystal lattice effectively without changing the main phase structure. As a result, the luminous intensity of samples doped Ca2+ and Sr2+ increased by 39.7% and 41.2%, respectively. The mechanisms for such improvement is ascribed to the reduction of Eu3+ into Eu2+ under the lager volume of [EuO 9 ] 2 polyhedron. The treated samples exhibited relatively superior thermal stability with I 150°C > 70%, indicating that doping with Ca2+ or Sr2+ have no effect on the thermal stability. A pc-WLED device fabricated by combining (Ba,Sr) 2 SiO 4 :Eu2+, (Ca,Sr)AlSiN 3 :Eu2+, BaSi 2 O 2 N 2 :Eu2+ and KBa 0.86 Ca 0.1 YSi 2 O 7 :Eu2+ with 380 nm chip exhibits CCT (5010 K) and high CRI (96.6). These results indicate that this phosphor has potential for applications in full-spectrum warm white lighting. • The luminous intensity of KBa 0.96 YSi 2 O 7 :Eu2+ doped Ca2+ and Sr2+ increased by 39.7% and 41.2%, respectively. • The effective concentration of Eu2+ ions was enhanced by structural modulation. • A white-LED device with an excellent CRI (Ra = 96.6) and low CCT (5010 K) was obtained. [ABSTRACT FROM AUTHOR]

Eu-doped BaAlO red phosphors were synthesized by high-temperature solid-state reaction. The crystal structure, morphology and luminescence properties were investigated by XRD, TEM and photoluminescence spectroscopy. The effect of calcination temperature, Eu concentration as well as charge compensators on the luminescence properties was also investigated. Characteristic orange-red emission at 589 nm was detected under 394 nm excitation. The best performance could be derived for the sample calcined at 1450 °C. With the increase of Eu concentration, the emission intensities increased gradually up to the Eu concentration of 12 %. The emission intensities could be enhanced with Li, Na and K introduced as charge compensators. The results showed that BaAlO:Eu phosphors with charge compensator had potential application in the fields of near-UV-excited WLEDs. [ABSTRACT FROM AUTHOR]

• A brand-new blue-emitting phosphor NaSrScSi 2 O 7 :Eu2+ was prepared. • NaSrScSi 2 O 7 :0.03Eu2+phosphor possesses a high absorption efficiency of 84.35%. • The blue phosphor allows the WLED-2 spectrum to cover more short-wavelength region. A high absorption efficiency blue-emitting phosphor NaSrScSi 2 O 7 :Eu2+ for near-UV-pumped white light-emitting diodes [Display omitted] The Eu2+ ion is extensively used as an activator due to its wide excitation band and high efficiency emission spectrum. However, most Eu2+-activated blue-emitting phosphors have low absorption efficiency in the near-ultraviolet (n-UV) region or lack the short-wavelength blue light emission (<450 nm), resulting in UV light leakage or poor color rendering. Herein, we have successfully prepared a brand-new blue phosphor NaSrScSi 2 O 7 : Eu2+ by solid-state reaction method. The Rietveld refinement of the powder diffraction data, luminescent properties, decay lifetime, quantum efficiencyand thermal quenching have been investigated in detail. Under 345 nm excitation, the NaSrScSi 2 O 7 : 0.03Eu2+phosphor manifests an asymmetric emission spectrum centered at 427 nm, and notably, shows a high absorption efficiency of 84.35%. Finally, we encapsulated two white light-emitting diodes (WLEDs) devices using as-prepared blue-emitting phosphor and three commercial phosphors. At 80 mA drive current, both packaged devices demonstrate warm white light. Meanwhile, the WLED-2 with NaSrScSi 2 O 7 : 0.03Eu2+ blue-emitting phosphor has a lower correlated color temperature of 3726 K, its spectrum complements more short-wavelength spectrum, and the special color rendering index R 6 and R 7 increased from 95.2, 94.5 to 98.3, 96.5, respectively, compared with WLED-1 without present phosphor. These results demonstrate that NaSrScSi 2 O 7 : Eu2+ blue-emitting phosphor is a prospective novel luminescent material for WLEDs. [ABSTRACT FROM AUTHOR]

Mn4+-activated (oxy)fluoride-based red phosphors have received extensive attention. In this work, a phase transformation from K 2 NbF 7 to K 3 HF 2 NbOF 5 was successfully achieved by stoichiometric control during coprecipitation process, resulting in a novel red phosphor K 3 HF 2 NbOF 5 :Mn4+ with narrow-band emission. A systematic study was carried out on its crystal structure and luminescent properties. By introducing O ions into the local coordinated structure, the emission intensity of K 3 HF 2 NbOF 5 :Mn4+ phosphors is 2.15 times as high as that of K 2 NbF 7 :Mn4+ with a photoluminescence internal quantum yield (IQE) of 73.28% and absorption efficiency (AE) of 49.68%, which could be attributed to the layered structure of the oxyfluoride host. High quenching concentration of 8.39 mol% and short decay lifetime of 4.19 ms are realized. Based on K 3 HF 2 NbOF 5 :Mn4+ and commercial YAG:Ce3+, a white light-emitting diode (WLED) for solid state lighting was fabricated, which has low CCT of 3802 K, high Ra of 86.3 and high luminous efficiency (LE) of 126.23 lm/W. Moreover, by employing commercial β-sialon:Eu2+ and K 3 HF 2 NbOF 5 :8.39%Mn4+, another WLED with high LE of 95.78 lm/W and wide color gamut of 108.6% National Television Standard Committee (NTSC) standard for backlight lighting was packaged, indicating a great potential of K 3 HF 2 NbOF 5 :Mn4+ as a red component in the application of backlight lighting. • Phase transformation from K 2 NbF 7 to K 3 HF 2 NbOF 5 was achieved by stoichiometric control. • Accompanying with fluoride to oxyfluoride phase transformation, the fluorescence intensity was greatly enhanced. • High photoluminescence quantum yield, wide color gamut and short fluorescence lifetime suit backlight applications. [ABSTRACT FROM AUTHOR]

• A cyan emission was achieved via the replacement of Si-N with Al-O in Ba 3 Si 6 O 12 N 2 :0.05Eu2+. • The emission peak could be shifted from 512 nm to 495 nm. • The emission intensity of the optimal cyan phosphor is 36% higher than Ba 3 Si 6 O 12 N 2 :0.05Eu2+. • The CCT of wLED decreases from 4407 K to 4038 K and the Ra increase from 85.8 to 90.8. Developing cyan phosphors excited by near ultraviolet (n-UV) or blue LED chips is extremely significant for making up for the cyan cavity of the existing white light emitting diodes (wLEDs). In this research, a cyan emission was successfully achieved via the replacement of Si-N with Al-O in Ba 2.85 Si 6 O 12 N 2 :0.15Eu2+ green phosphor. The emission peak could be shifted from 512 nm to 495 nm. The mechanism of spectral blue shift can be interpreted by the decrease of the crystal field splitting strength, which is induced by the square of the bond length and the decrease of centroid shift of 5d level, which is induced by the spectroscopic polarizability and 6th power of the bond length. The optimal cyan Ba 2.85 Si 5.65 Al 0.35 O 12.35 N 1.65 :0.15Eu2+ phosphor possess a broad excitation and emission band at the same time, whose emission intensity is 36% higher than that of Ba 2.85 Si 6 O 12 N 2 :0.15Eu2+. The CCT of the wLED with Ba 2.85 Si 5.65 Al 0.35 O 12.35 N 1.65 :0.15Eu2+ phosphor realizes from 4407 K to 4038 K and the Ra values achieve from 85.8 to 90.8. The results indicate that Ba 2.85 Si 6- y Al y O 12+ y N 2- y :0.15Eu2+ phosphor can serve as a cyan component for application in full-spectrum warm white lighting. [ABSTRACT FROM AUTHOR]

In this study, Ca 2.98 SiO 4 Cl 2-y Br y :0.02Eu2+ cyan-green phosphors with high efficiency and good thermal stability were prepared by a low temperature synthesis. The crystal structure, luminescence properties and thermal stability of as-prepared phosphors were systematically investigated by means of X-ray diffraction (XRD), photoluminescence excitation spectra (PLE), photoluminescence spectra (PL), CIE coordinates and variable temperature spectra. Simply increasing Br− in Ca 2.98 SiO 4 Cl 2-y Br y :0.02Eu2+, the emission peak can be shifted from 502 nm to 491 nm under near-UV (n-UV) excitation, which can make amends for the cyan gap (480–520 nm) and realize high color rendering. The remarkable blue shift of the emission band can be ascribed to the small crystal field splitting and Stokes shift. The external quantum efficiency of Ca 3 SiO 4 ClBr:Eu2+ moves up to 55.58% and exhibits an impressively absorption efficiency. Furthermore, a white LED device was fabricated via blue-emitting Sr 5 (PO 4) 3 Cl:Eu2+, green-emitting YAGG:Ce3+, red-emitting (Ca,Sr)AlSiN 3 :Eu2+, and the cyan phosphor Ca 3 SiO 4 (Cl,Br) 2 :Eu2+ with 410 nm-chip. The WLED exhibits a warm and bright white light with low correlated CCT (3969 K), high Ra (96.9), and CIE color coordinates of (0.3828,0.3810). The results indicate that Ca 2.98 SiO 4 Cl 2-y Br y :0.02Eu2+ can be used as a potential cyan phosphor for full-spectrum warm white LED. • Novel cyan-green phosphors Ca 2.98 SiO 4 Cl 2-y Br y :0.02Eu2+ for full-spectrum warm white LED were prepared. • High CRI (96.9) and low correlated CCT (3969 K) white LED was fabricated. • The mechanism of blue shift of the emission band was analyzed. [ABSTRACT FROM AUTHOR]

La 3 Si 6 N 11 :Ce3+ (LSN:Ce3+) phosphor has attracted widespread attention in the field of high-power white light-emitting diodes as it can be effectively excited by blue LED chip and exhibits excellent thermal quenching. To improve the emission intensity is always the critical objective of La 3 Si 6 N 11 :Ce3+. In this paper, the strategy by combining CeO 2 and CeN as cerium sources of the activator was developed to enhance the emission intensity. The emission intensity of NO-LSN:Ce3+ is 112.8% of that of N-LSN:Ce3+, which benefits from the enhancement of the concentration of Ce3+ ions. Generally, more Ce4+ ions can enter into the lattice of La 3 Si 6 N 11 at high concentration due to the smaller ionic radius of Ce4+ than Ce3+. After that, Ce4+ ions can be effectively reduced to Ce3+ ions at high temperature. The luminescence improvement mechanism of as-prepared phosphors was analyzed. This research provides an effective method for improving the emission intensity of nitride or oxy-nitride phosphors. • The effects of CeO2 and CeN co-doping on emission intensity of LSN phosphor was first studied. • The mechanism of CeO2 and CeN co-doping LSN on emission intensity was analyzed. • This study provides a strategy for improving the emission intensity of LSN:Ce3+. [ABSTRACT FROM AUTHOR]

It is well known that green-emitting phosphor plays a key role in a phosphor-converted white LED with high color rendering index. Here, a novel green phosphor BaY 1·95 Al 2 Ga 2 SiO 12 :0.05Ce3+ with high quantum yield, low thermal quenching and excellent water resistance is reported. The green phosphor can be easily prepared by the conventional solid-state reaction method at 1325 °C for 4 h in a reducing atmosphere. The compound is cubic and crystallizes in space group I a 3 ‾ d with refined lattice parameters of a = 12.1451(3) Å. The phosphor can be effectively excited by the mainstream commercial blue LEDs (445–465 nm), its emission peak is observed at 517 nm and the absolute quantum yield under 450 nm excitation is as high as 96.2% at 25 °C. The green phosphor exhibits good resistance toward thermal quenching, with the luminescence intensity at 150 °C only decreasing by 11% of the value at 25 °C. In addition, the green phosphor has a very good water resistance, and its luminescence intensity remains almost unchanged when it is soaked in water for more than 300 h. The white LED fabricated by employing the green phosphor shows excellent optical properties with Ra = 92.4, CCT = 3304 K and CIE 1931 chromaticity coordinates as (x = 0.4178, y = 0.3985). All experimental results indicate that BaY 1·95 Al 2 Ga 2 SiO 12 :0.05Ce3+ is an outstanding green phosphor which has great potential to be used for the phosphor-converted white LEDs with excellent color rendering. • BaY 1·95 Al 2 Ga 2 SiO 12 :0.05Ce3+ is a novel blue-light excitable green-emitting phosphor. • Its absolute quantum yield under 450 nm excitation is as high as 96.2%. • Its emission intensity at 150 °C only decreases by 11% of the value at 25 °C. • Its emission intensity remains almost unchanged when soaked in water for 312 h. [ABSTRACT FROM AUTHOR]

• A novel CsMoO 2 F 3 :Mn4+ oxyfluoride phosphor with high color purity was synthesized. • The CsMoO 2 F 3 :Mn4+ phosphor exhibits a remarkable negative thermal quenching. • The CsMoO 2 F 3 :Mn4+ phosphor demonstrates admirable color stability. Red-emitting phosphors composed of Mn4+-activated fluorides have attracted considerable interest for their applications in warm white light-emitting diodes (WLEDs). However, in addition to moisture instability, the unsatisfactory thermal stability of these phosphors limits their industrial applications. In this study, a novel red phosphor of CsMoO 2 F 3 :Mn4+ was synthesized via simple coprecipitation. This red phosphor exhibits an orthorhombic structure with a bandgap of ~3.43 eV. The Mn4+ ions occupy Mo6+ sites at the centers of [MoO 2 F 4 ]2− octahedrons. This phosphor shows narrow emission around ~633 nm excited by 450 nm blue-chip with high color purity of 99.58%. Satisfactorily, this phosphor exhibits excellent thermal stability and a strong negative-thermal-quenching. The total PL intensity of CsMoO 2 F 3 :3.88%Mn4+ phosphor at 275 K strengthens to ~540% relative to that at 25 K, and its relative emission intensity preserves about 129.3% when the temperature rises from room temperature to 423 K (150 ℃). It also shows admirable color stability with a slight chromaticity shift (ΔE) of only ~ 33.9 × 10 - 3 in the temperature region from 298 to 473 K. Furthermore, a warm WLED was fabricated by the mixture of red-emitting CsMoO 2 F 3 :3.88%Mn4+ and the yellow-emitting YAG:Ce3+ phosphors with a blue-emitting InGaN LED chip. The device exhibits low correlated color temperature (3983 K) and high color-rendering index (Ra = 81.3). With the increasing drive current from 20 mA to 120 mA, the chromaticity coordinate variation (CCV) is only (−0.0163, 0.0202). All these results indicate that the CsMoO 2 F 3 :Mn4+ phosphor holds tremendous potential for practical applications in high-power lighting and display with high-performance WLEDs. [ABSTRACT FROM AUTHOR]

• The highest energy transfer efficiency of Eu2+ → Mn2+ can achieve about 78 %. • The integrated emission intensity of Al 5 O 6 N:Eu2+, Mn2+ at 150 ℃ can maintain 82 %. • The tunable color emission of the samples can be realized tuned from blue to green. A series of Eu2+ and Mn2+ co-activated Al 5 O 6 N multi-color phosphors were fabricated through the gas-pressure sintering method, and they displayed intense blue-green emitting at near-ultraviolet irradiation due to efficient energy transfer. Dipole-dipole interaction was proved to be the leading role for Eu2+-Mn2+energy transfer and the highest energy transfer efficiency was obtained about 78 %. Furthermore, tunable emissions from blue to green were observed through regulating the concentration of Eu2+ and Mn2+. In addition, the temperature-dependent luminescence behavior of Al 5 O 6 N:Eu2+, Mn2+ was examined, and the emission intensity at 150℃ maintains 82 % of initial intensity, which indicates superior thermal stability. These outcomes illustrate that the Al 5 O 6 N: Eu2+, Mn2+ phosphors may be potentially used in white LEDs. [ABSTRACT FROM AUTHOR]