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 K₂YZr_1–yHf_y(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 (R_a = 81) and a correlated color temperature (CCT = 3792 K).