Tunable chromaticity and enhanced luminous efficacy of white LEDs with phosphor-in-glass coating via multilayer screen-printing

The phosphor-in-glass (PiG) coating was fabricated via multilayer screen-printing and low-temperature sintering. The PiG coating consisted of Eu2O3-doped P2O5-ZnO-B2O3 (PZB) glass, Y3Al5O12:Ce3+ (YAG:Ce) yellow phosphor, and CaAlSiN3:Eu2+ (CASN:Eu) red phosphor. Eu2O3 and CASN:Eu were used to provide red emission for tunable chromaticity of white light-emitting diodes (LEDs), and surprisingly, the luminous efficacy was also enhanced. The impact of the variation in the B2O3 content on the PZB glass and the effect of Eu2O3, YAG: Ce, and CASN:Eu on the luminescent properties of the PiG coating were investigated. The glass matrix with 8 mol% B2O3 showed the lowest transition temperature and a suitable coefficient of thermal expansion. The spectra showed that the coating can be excited by blue light and produce yellow light and red light. The spatial distribution of the PiG coating was inspected by scanning electron microscopy, and it was observed that only a low erosion of phosphor by the glass matrix occurred. Furthermore, the white LEDs devices were constructed with the PiG coating on the blue LED chips. This method showed a decreased correlated colour temperature of 5137, a increased colour rendering index of 82.8 and an improvement in the luminous efficacy. The PiG coating for tunable chromaticity and enhanced luminous efficacy of white LEDs shows potential for application.