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 Mn 4+ ions doped Ca 2 YTaO 6 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 P 2 1 / n with lattice parameters of a  = 5.59630(8) Å, b  = 5.82308(8) Å, c  = 8.07158(12) Å, α = γ =  90 ° , β  = 89.9768(23)°, and V =  263.034(4) Å 3 . The Ca 2 YTaO 6 structure consisted of abundant [TaO 6 ] octahedrons, providing appropriate sites for Mn 4+ incorporation. As obtained by photoluminescence measurements, the Ca 2 YTaO 6 :Mn 4+ 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 2 E g  →  4 A 2g transition of Mn 4+ ions. The investigation of the doping concentration-dependent optical properties of Ca 2 YTaO 6 :Mn 4+ phosphors indicated the critical quenching concentration equal to 0.2 mol%. The dipole-dipole   interaction between   Mn 4+ activators was the major mechanism leading to the concentration quenching effect. The fluorescence decay lifetimes of Ca 2 YTaO 6 :Mn 4+ phosphors decreased from 0.34 to 0.201 ms with increasing Mn 4+ 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 Ca 2 YTaO 6 :0.2%Mn 4+ sample was measured to be 21%.