||In this study, we used multi-phosphor-doped sodium glass (MPDG) as color conversion layer, and successfully developed glass phosphor with high color rendering index (CRI) and high reliability. We study the optical properties and microstructure of MPDG in this experiment. We used yellow phosphor of YAG based (Y3AlO12 : Ce3+), green phosphor of LuAG based (Lu3Al5O12 : Ce3+), and red phosphor of nitride based (CaAlClSiN3 : Eu2+) sintering to be glass phosphor at 680℃, 700℃ and 750℃, respectively. The study indicates that the yellow and green glass phosphor can keep the same quantum yield (QY) at different sintering temperature. However, the QY of red glass phosphor is significantly reduced with rising temperature.|
The reason of the lowering QY of red glass phosphor can be explained by microstructure analysis when sintered at high temperature, the low temperature glass will diffuse into the phosphor crystal. Field-Emission Transmission Electron Microscope (FE-TEM) clearly shows that the higher sintering temperature induces thicker diffusion layer and more diffusion into phosphor crystal. Element analysis by Energy Dispersive System (EDS) reveals that, for red glass phosphor, higher percentage of carbon atoms in the diffusion layer under high sintering temperature, indicating more carbide was produced at higher temperature in the mixture of nitride phosphor and glass. The carbide severely lowered the quantum yield of the red glass phosphors.
Employing multi-phosphor (yellow, green, red) with doping concentration 0:4:1, and sintered at 680℃. Using a blue LED 445nm of wavelength as pumping source. The QY reaches 51%. The Color Coordinator and Correlated Color Temperature (CCT) of white light emitting diode (WLED) with them as color conversion layer is (0.317, 0.315；6336K). The CRI is up to 90, which meets the regulations of U.S. Energy Star that the CRI for interior lighting must exceed 80. The luminescence loss of glass phosphor is 5 to 10 space times lower than the traditional silicone phosphor under the 1008 hours reliability test under 150℃ and 250℃, respectively, which has great potential in lighting system.