Mapping the glass forming region and making their phosphor-in-glass for application in W-LEDs packaging

The application of phosphor-in-glass (PiG) packaging material in white-light emitting diodes (W-LEDs) can improve the thermal stability and luminous efficacy of LED devices. In this work, a low melting point glass of TeO2-ZnO-Na2O-B2O3 (TZNB) was selected as glass matrix, and mixed with YAG: Ce3+ phosphor powders to obtain phosphor-in-tellurite glass (PiTG). In a significant advance, we mapped the glass forming region of TZNB for the first time. This high refractive index glass matrix with low melting temperature was achieved by optimizing the glass composition. The refractive index increased regularly from 1.61 to 2.03, when the dosage of TeO2 increased from 15 to 75 mol%. Through Monte Carlo simulations and numerical calculations, the optimal structure of gradient refractive index (GRIN) was designed, which is consisted of TZNB-1 (n = 2.03), TZNB-4 (n = 1.79), TZNB-6 (n = 1.66), and glass substrate (n = 1.52). The PiTG with GRIN coating was fabricated by screen printing and low-temperature sintering, and the optimized sintering temperature is 575 degrees C. Compared with the single refractive index (SRIN) coating, the luminous efficacy of PiTG with GRIN coating was enhanced from 9.51% to 23.12%. Therefore, this work provides a significant application in high-power W-LEDs.