Double-site Eu3+ occupation in the langbeinite-type phosphate phosphor toward adjustable emission for pc-WLEDs

Highlights: • A new Eu³⁺-activated KBaIn₂(PO₄)₃ phosphor was prepared via solid-state method. • The prepared phosphors emitted color-tunable light under effectively excitation by near-UV and blue light. • The phosphor has a good luminescence thermal stability. • The as-prepared LED device can emit bright white light under high voltage and high current. -- Abstract: A novel single trivalent Eu ion activated multicolor tunable langbeinite-type phosphor KBaIn₂(PO₄)₃:Eu³⁺ (abbreviated to KBIP:Eu³⁺) was successfully synthesized through solid-state reaction. XRD was used to identify the phase of the as-prepared KBIP:Eu³⁺ phosphor, which proved that the phosphor was pure phase. The refined results showed that In³⁺ ions occupied two different sites in the KBIP host lattice. The PL spectra shows that the KBIP:Eu³⁺ phosphor has two luminescent centers, so Eu³⁺ ions can replace In³⁺ ions with two different positions. With the change of doping concentration, Eu³⁺ ions have different occupation orientations in the two sites, and tunable luminescence occurs at different excitation wavelengths. Besides, the morphology, molecular structure and optical properties of the KBIP:Eu³⁺ phosphors were studied. It is found that the sample crystallizes completely, and the band gap minishes from 2.67 eV to 2.36 eV with the increase of Eu³⁺ doping content. The fluorescence intensity at 150 ℃ is 65.5% of that at room temperature, and the calculated activation energy is 0.20 eV. The simple LED device test shows that the color rendering index of the phosphor is high (R_a = 92.4%), which greatly improves the red index R₉. Therefore, the reported phosphors have great potential application in pc-WLEDs in the future.