Up-conversion phosphor plate for white lighting device using NIR excitation source

Abstract

Upconversion phosphors have numerous advantages compared to down conversion phosphor materials, such as a weak background interface, low excitation energy, sharp emission lines, and long lifetimes. Conventionally, blue laser diodes are used to obtain strong white light by combining green- and red-emitting phosphors. The blue-excited white-light-emitting devices can be harmful when the blue light penetrates directly into the human body. However, lower energy excited lighting devices does not harm the human body because of their low-energy photons are compatible with the biologically safe window. Hence, we present a prototype device that converts invisible near-infrared light into visible white light. For this, we synthesized orange-emitting Y2O3:Er3+, Yb3+ and blue-emitting Y2O3:Tm3+, Yb3+ upconversion phosphors using a solid-state reaction. Using these, phosphor-in-glass (PiG) samples with sintered glass frit were prepared to investigate their optical behavior under low-excitation energy. The emission color from the stacked PiGs depends on the color balance between the activator ions of Er3+, Tm3+, and Yb3+, and their balance is optimized to obtain a white light. The results might pave the way for designing safe white-light-emitting devices using a low-energy excitation source.