Structure-Properties Correlations in Whitlockite-Type Ultra-Narrow Red Phosphors Ca9– X Sr X In(Vo4)7

Abstract

Ca9–xSrxIn(VO4)7 (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 Ca9–xSrxIn(VO4)7 have a non-centrosymmetric structure (space group R3c). 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 (10%)) in solid solutions. The magnitude of the SHG signal lowers with increasing Sr2+ concentration. The concentration behavior of Eu3+ photoluminescence in Ca9–xSrxIn(VO4)7:Eu3+ shows a non-linear dependence, with the maximum at x = 4.5. The obtained PL spectra show ultra-narrow intensive red emission (FWHM = 5 nm). The color coordinates completely match with red standard. Ca9–xSrxIn(VO4)7:Eu3+ phosphors have an extremely high colour purity. The obtained phosphors can be used for improvement of the CRI in wLEDs.

Keywords: vanadates, whitlockite, TCP, luminescence, nonlinear optics