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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]

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]

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]

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]

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]

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]

• 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]

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]

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 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]

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]

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]

• 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]

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]