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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]

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]

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]

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 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]