Luminescence mechanism and optical properties of apatite-type Ca10(PO4)6F2:Eu3+ phosphors

Abstract

A series of new apatite-type red-emitting Ca₁₀(PO₄)₆F₂:Eu³⁺ phosphors have been synthesized via the hydrothermal method. The Rietveld refinement results indicate that when the Eu doping concentration is less than 14 mol.%, the phosphor maintains a pure fluorapatite phase with no detectable impurities, and the Eu³⁺ ions preferentially occupy the Ca2 sites within the host lattice. The PL emission spectrum under the excitation of 352 nm consists of the highest emission band (618 nm) and four relatively weak emission bands (579 nm, 591 nm, 653 nm and 696 nm) which correspond to the ⁵D₀→⁷F_J transitions (J = 0, 1, 2, 3 and 4). The emission intensity decreases at concentrations above 10 mol.%, due to dipole-dipole interactions and concentration quenching. The Commission Internationale de l’Éclairage (CIE) chromaticity coordinate of the Ca₁₀(PO₄)₆F₂:Eu³⁺ (x = 10 mol.%) phosphor is near (0.6341,0.3652). The color purity is approximately 86.95 % and the internal quantum yield is 62.8 %. The activation energy for thermal quenching for this phosphor is 0.29 eV, and more than 50 % of its emission intensity is retained at 498 K, demonstrating excellent thermal stability. Owing to their outstanding thermal quenching luminescence properties, the Ca₁₀(PO₄)₆F₂:Eu³⁺ phosphors are well-suited for application in white-LEDs, acting as the red-emitting component in warm white light generation.