Enhanced luminous efficiency of multilayer gradient refractive index phosphor in P2O5-ZnO-B2O3-BaO glass for white light-emitting diode packages

Abstract A multilayer gradient refractive index (GRIN) phosphor in glass (PiG) on Boron-silicate glass substrate is introduced to improve the luminous efficiency of white light-emitting diode (WLED) packages. The multilayer PiG coating employing gradual altering refractive index (RI) P 2 O 5 -ZnO-B 2 O 3 -BaO (PZBB) glass is fabricated using multilayer screen-printing and low-temperature sintering. Properties of PZBB glass, surface topography, transmittance, and luminous efficiency of phosphor in PZBB glass with GRIN are investigated. The results demonstrated that when barium oxide is added from 0 to 20 mol%, coefficient of thermal expansion (CTE), glass transformation temperature (Tg), and RI increase from 84.00 to 97.91 ∗ 10 − 7 /K, 390.3 to 445.2 °C, and 1.42 to 1.58, respectively. PZBB glass with RI values of 1.51, 1.54 and 1.58 is synthesized in PiG to achieve GRIN. After sintering at 600 °C for 30 min, phosphor in PZBB glass with GRIN still retains a perfect surface, which indicates its CTE of interfacing layers are matched. Transmittance of phosphor in PZBB glass with GRIN increases when adding GRIN layers, and the luminous efficiency is enhanced over 28.87%, compared to that of PiG with conventional structure.