Effect of co-doping of alkali metal ions on Ca0.5RE1−x(MoO4)2:xEu3+ (RE = Y, La) phosphors with enhanced luminescence properties

Abstract

A series of Ca_0.5RE_1−x(MoO₄)₂:xEu³⁺,M⁺ (RE = Y, La; M = Li, K and Na) phosphors were synthesized by a facile hydrothermal method. X-ray diffraction suggested that these phosphors could be indexed to a scheelite tetragonal Ca_0.5RE_1−x(MoO₄)₂ (RE = Y, La) phase with a space group of I4₁/a with high purity. FESEM indicated the signs of bi-pyramid-like micro-architectures. Elemental mapping analysis provided evidence of the incorporation and uniform distribution of all the elements. X-ray photoelectron spectroscopy (XPS) confirmed the presence of all the elements. The PL properties of Ca_0.5RE_1−x(MoO₄)₂:xEu³⁺,M⁺ (RE = Y, La; M = Li, K and Na) phosphors were analysed extensively. The obtained results suggest that the characteristic red emission is due to the hypersensitive electric dipole ⁵D₀ → ⁷F₂ transition. The emission intensity of Ca_0.5RE_1−x(MoO₄)₂:xEu³⁺,Na⁺ (RE = Y, La) is higher than Li⁺ and K⁺ co-doped Ca_0.5RE_1−x(MoO₄)₂:xEu³⁺ (RE = Y, La). This can be explained by the charge compensation effect. Judd–Ofelt theory was adopted to examine the photophysical properties. The luminescence decay time values were estimated. The CIE chromaticity co-ordinates were derived from the emission spectra and the values were found to be close to the NTSC standard values. Hence, the prepared phosphors are suitable for display applications.