Thermally Stable Phosphor KBa₂(PO₃)₅:Eu²⁺ with Broad-Band Cyan Emission Caused by Multisite Occupancy of Eu²⁺

The relationship between the structure and properties is always a hot topic in the luminescent material field. In this work, a new phosphor KBa₂(PO₃)₅:Eu²⁺ (KBP:Eu) was prepared by a high-temperature solid-state reaction method and characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy, photoluminescence (PL), and electroluminescence studies. The polyphosphate host KBP offers three lattice environments (K1, Ba1, and Ba2) for Eu²⁺ ions to realize broad-band emission from 380 to 700 nm under 345 nm excitation. The distributions of Eu²⁺ in the three lattice sites can be proven by low-temperature PL and transient fluorescence spectroscopy. Furthermore, temperature-dependent luminescence studies for phosphor KBP:0.02Eu reveal that its luminescence intensity at 150 °C retains about 97% of the initial value at 25 °C. By composing a 365 nm UV chip and KBP:0.02Eu, CaAlSiN₃:Eu²⁺ phosphors, a warm white-light-emitting diode (WLED) was obtained with a correlated color temperature of 5146 K and chromaticity coordinates (0.3404, 0.3384). Therefore, KBP:Eu phosphor is a potential cyan-emitting phosphor used for high-power WLEDs.