Structure-properties correlations in whitlockite-type ultra-narrow red phosphors Ca9−xSrxIn(VO4)7

Ca_9−xSr_xIn(VO₄)₇:Eu³⁺ (0 ≤ х ≤ 9) solid solutions with the β-Ca₃(PO₄)₂-type structure were prepared using a standard solid-state method. The combination of the X-ray diffraction and second harmonic generation methods revealed that Ca_9−xSr_xIn(VO₄)₇ have a non-centrosymmetric structure. The existence of a reversible phase transition ferroelectric-paraelectric was established. The substitution of Ca²⁺ ions by large Sr²⁺ ions is accompanied by record linear expansion of the unit cell volume. The magnitude of the SHG signal lowers with increasing Sr²⁺ concentration. The concentration behavior of Eu³⁺ photoluminescence shows a non-linear dependence, with the maximum at x = 4.5. The PL intensity under 465 nm excitation is higher (in 4 times) in relation to the 395 nm. The obtained PL spectra show ultra-narrow intensive red emission (FWHM = 5 nm). The color coordinates completely match with red standard. The obtained phosphors can be used for improvement of the CRI in wLEDs.