Two-Site Occupancy Induced a Broad-Band Emission in Phosphor K2YZr(PO4)3:Eu2+ for White-Light-Emitting Diode Applications

Developing broad-band-emitting phosphors is very important to light-emitting diode (LED) lighting and displays. We introduced Eu2+ to solid solutions K2YZr1–yHfy(PO4)3 with a langbeinite-type structure to prepare a series of new phosphors. In this structure, two K+ sites could be occupied by Eu2+ cations to provide two different kinds of coordination environments, leading to broad emitting bands in the range of 390–700 nm. The coordination circumstance of Eu2+ was analyzed by Gaussian fitting and time-resolved emission spectra. Furthermore, the emitting intensity and thermal stability can be improved by modulating the crystalline field via substituting Zr4+ by Hf4+. When the Zr4+ was fully substituted by Hf4+, the external quantum efficiency increased by 53.75%, giving a bright cyan emission. Finally, an archetype white-LED lamp was made using cyan phosphor K2YHf(PO4)3:0.04Eu, red phosphor CaAlSiN3:Eu2+, and a 365 nm LED chip, which realized an applicable color rendering index (Ra = 81) and a correlated color temperature (CCT = 3792 K).