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In this study, Cr3+‐doped and Mn4+‐Cr3+ co‐doped double perovskite fluoride phosphors K2LiGaF6 are prepared using a simple hydrothermal method. High‐efficiency near‐infrared (NIR) emission near 762 nm is obtained under blue‐light excitation, and the co‐doping effect of Mn4+ on the NIR luminescence properties of Cr3+ is studied. Compared with the Cr3+ single‐doped phosphor, Mn4+, and Cr3+ co‐doped K2LiGaF6 exhibit a sharp increase of 129% in NIR emission, an enhancement in the internal quantum efficiency from 82.5% to 90.0%, and an enhancement in the thermal stability at 425 K from 85.0% to 90.7%. The encapsulated NIR phosphor‐converted light‐emitting diode device at 300 mA exhibits a photoelectric conversion efficiency of 15.3%. These values exceed most previously reported results. This study provides a new approach for enhancing the luminescence properties of Cr3+‐doped fluoride NIR phosphors. [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]

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]

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]

Supplement illumination is indispensable in the indoor plant cultivation domain. In this research work, double perovskite Ca 2 LuNbO 6 :Mn4+ phosphors were produced. A strategy of enhancing luminescence performance by utilizing A-site cationic fluoride as a flux was proposed. The structure and morphology of Ca 2 LuNbO 6 :Mn4+ phosphor was characterized. Under the excitation of 360 nm, the emission spectra of Ca 2 LuNbO 6 :Mn4+ phosphor cover from 600 nm to 750 nm peaking at 683 nm. It benefits the red section of chlorophyll absorption band and possesses the wavelengths of 680 nm and 700 nm demanded by photosystem I (PS I) and photosystem II (PS II) to realize Emerson enhancement effect. After adding CaF 2 as flux, the emission intensity increases by 2.5 times. Due to its compatibility with the A-site cation of host, CaF 2 agent not only lower the sintering temperature but also increase the crystallite size, which result in the enhancement of luminescence. The D q /B and optical band gap of Ca 2 LuNbO 6 host is 2.32 and 3.79 eV, respectively, which show that Mn4+ ions locate in the [NbO 6 ] octahedra of strong crystal field and host has the suitable optical band gap for Mn4+ ions. With the help of CaF 2 , the thermal stability, activation energy Δ E a , internal quantum efficiency of Ca 2 LuNbO 6 :Mn4+ phosphors are promoted at 373 K from 64.8% to 70.7% of that at 273 K, from 0.33 to 0.36 eV, and from 9.1% to 23.5%. The luminescence lifetime of Ca 2 LuNbO 6 :Mn4+ is the order of a fraction of a millisecond. Finally, the as-prepared Ca 2 LuNb 0.996 O 6 :0.004Mn4+ phosphor was successfully fabricated through a 365 nm near ultraviolet (NUV) chip, which has the peak wavelengths of 683 nm and possesses 680 nm and 700 nm demanded by PS I and PS II. It is implied that Ca 2 LuNbO 6 :Mn4+ phosphor-converted light emitting diode has prospective market in the domain of supplement illumination of plant cultivation. [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]

The development of thermally stable and efficient broadband near-infrared (NIR) phosphors suffers from severe hindrance. Herein, a unique anti-fluorescence quenching is realized in a novel Cs 2 NaGaF 6 : Cr3+ NIR fluoride phosphor with a strategy of integrating the structural confinement effect with weak electron-phonon coupling effect. Upon blue light excitation, this phosphor exhibits a wide emission band with a peak wavelength of ∼789 nm and a full width at half maximum (FWHM) of 117 nm. Thanks to the structural confinement effect, a large quenching content of 20 mol% and a high internal quantum efficiency (IQE) of 87.4% are achieved, showing a suppressed concentration quenching behavior. Significantly, Cs 2 NaGaF 6 : 0.20Cr3+ phosphor possesses an abnormal zero thermal quenching, which could be related with the weaker electron-phonon coupling effect. The emission intensity of Cs 2 NaGaF 6 : 0.20Cr3+ at 423 K can maintain up to 101.96% of that at 298 K. A fabricated NIR phosphor-converted light-emitting diode (pc-LED) exhibits an output power of 57.71 mW and a photoelectric conversion efficiency as high as 19.24% at 100 mA. Finally, utilizing a high-power NIR LED as the illuminant for traffic surveillance, significant information can be captured even in low-visibility environments. As a result, Cs 2 NaGaF 6 : Cr3+ possesses tremendous prospects in high-power NIR LEDs. [Display omitted] • A novel structure-confined fluoride NIR phosphor Cs 2 NaGaF 6 : Cr3+ was obtained. • Suppressed concentration quenching and high internal quantum efficiency of 87.4% were realized. • This phosphor possesses an abnormal zero thermal quenching effect (101.96% @423 K). • The NIR pc-LED device can be applied in traffic surveillance. [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]

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]