Structure–Photoluminescence Relationship in Ce³⁺-Doped K₅Y(P₂O₇)₂ and Its Sensitization to Dy³⁺ with Enhanced White Light Emission

Abstract

From a fundamental point of view, the structure−photoluminescence relationship is vitally important for developing efficient phosphors and rationally improving their performances. In this work, Rietveld refinements on high-resolution powder X-ray diffraction (XRD) data were conducted to verify the Ce 3+ distribution in K 5 Y(P 2 O 7 ) 2 (KYPO). Ce 3+ ions are located at both M1 and M2 sites, with occupation factors of 0.31(2) and 0.19(2), respectively. Importantly, the crystal field strength (CFS) is stronger at the former site due to the larger bond valence sum. Correspondingly, the Ce 3+ emission can be deconvoluted into four Gaussian-type bands centered at ∼353, ∼383, ∼343, and ∼369 nm, where the former two belong to Ce 3+ at the M1 site and the latter two are assigned to Ce 3+ at the M2 site. Ce 3+ in KYPO is a highly efficient activator, with optimal internal and external quantum efficiencies of 98.9 and 74.6%, respectively, and was thus utilized to sensitize the Dy 3+ emission. Indeed, energy transfer from Ce 3+ to Dy 3+ was confirmed by fluorescent decay curves for Ce 3+ /Dy 3+ codoped KYPO, and the mechanism was supposed to be dominated by dipole−dipole interactions. Indeed, it can be pumped by a 310 nm LED chip and emits a bright white light. Ce 3+ photoluminescence exhibits high resistance to thermal quenching, and it can be further enhanced by codoping Dy 3+ , i.e. the emission intensity remains 96.3% at 423 K.