Structural analysis and Judd-Ofelt parameterization of Ca9Gd(PO4)7:Eu3+ nanophosphor for solid-state illumination

High-brightness, red-emitting Ca₉Gd_1−x(PO₄)₇:xEu³⁺ phosphors were developed via the facile route of solution-combustion. The Rietveld-assisted structural analysis of Ca₉Gd(PO₄)₇ and Ca₉Gd_0.40Eu_0.60(PO₄)₇ systems unveiled a trigonal crystal system having R3c(161) space-group symmetry. The absence of JCPDS data was compensated by simulating one from refined structural prototype. The band-gap for the host and best luminescent composition were determined to be 4.55 and 4.01 eV, respectively. The ratio of Judd-Ofelt parameters inferred a very high asymmetry around activator ion which can further be enhanced as a function of dopant concentration. The refractive index of Ca₉Gd(PO₄)₇ was determined to be 2.34. The value of stimulated emission cross section, total radiative transition rate and non-radiative transition rate for Ca₉Gd_0.40Eu_0.60(PO₄)₇ are calculated from detailed photo-luminescent (PL) analysis. Furthermore, very high value of quantum efficiency (98.13%) and radiative lifetime (1.85 ms) suggested that Ca₉Gd_0.40Eu_0.60(PO₄)₇ nanophosphor have practical applicability in PC-WLEDs (components of solid-state lighting).