Optical properties of deep-red-emitting Ca2YTaO6:Mn4+ phosphors for LEDs applications

Red-emitting phosphors are highly demanded as color converters for both white light-emitting diodes (LEDs) and plant growth LEDs. Herein, we reported on the discovery of novel Mn4+ ions doped Ca2YTaO6 double-perovskite red-emitting phosphors. These samples were successfully prepared via the high-temperature solid-state reaction method, and their phase purity was confirmed by powder X-ray diffraction (XRD) patterns. XRD Rietveld refinement results revealed that the title compound crystallized in monoclinic space group P2(1)/n with lattice parameters of a = 5.59630(8) angstrom, b = 5.82308(8) angstrom, c = 8.07158(12) angstrom, alpha = gamma = 90 degrees, beta = 89.9768(23)degrees, and V = 263.034(4) angstrom(3). The Ca2YTaO6 structure consisted of abundant [TaO6] octahedrons, providing appropriate sites for Mn4+ incorporation. As obtained by photoluminescence measurements, the Ca2YTaO6:Mn4+ phosphors showed a broadband excitation spectrum in the 250-600 nm wavelength range with two peaks around 350 and 514 nm. Under the 350 nm excitation, they exhibited narrowband deep-red emissions in the 630-750 nm wavelength range peaking at 680 nm with full-width at half maximum (FWHM) of 36 nm, corresponding to the spin-forbidden E-2(8) -> (4)A(28) transition of Mn4+ ions. The investigation of the doping concentration-dependent optical properties of Ca2YTaO6:Mn4+ phosphors indicated the critical quenching concentration equal to 0.2 mol %. The dipole-dipole interaction between Mn4+ activators was the major mechanism leading to the concentration quenching effect. The fluorescence decay lifetimes of Ca2YTaO6:Mn4+ phosphors decreased from 0.34 to 0.201 ms with increasing Mn4+ doping concentrations. The CIE chromaticity coordinates of these phosphors were calculated based on the emission spectra, and the color purity reached up to 98.3%. Besides, the internal quantum efficiency of the optimal Ca2YTaO6:0.2%Mn4+ sample was measured to be 21%.