Optical spectroscopy and thermally stable characteristics of Ce3+/Tb3+/Eu3+ triply doped Na5Y9F32 single crystals for white light emission

Abstract

Na5Y9F32 single crystals incorporated with fixed 0.4 mol% Ce3+, 0.5 mol% Eu3+ and various Tb3+ ion concentrations from 0.3 to 0.9 mol% were synthesized via Bridgman method. The effects of Tb3+ ion concentration and exciting wavelength on the fluorescence spectra of the single crystals were investigated in detail. Upon excitation of 320 nm light, as Tb3+ concentration increasing from 0.3 to 0.9 mol%, the 420 and 441 nm emission intensities of Ce3+ ion decrease continuously but the 544 nm of Tb3+, and 591 nm and 613 nm of Eu3+ increase. The energy transfers among Ce3+, Tb3+ and Eu3+ ions were responsible for the above changes of emissions, which was studied with help of the measured optical spectra and decay curves. Upon excitation of 320 nm, the emission of the triply doped crystal from the combination of 441, 544, 591 and 613 nm was changed from blue gamut with color coordinates (0.2993,0.2759）to white with color coordinates (0.2986,0.3208) as Tb3+ ion incorporating concentration change from 0.3 to 0.9 mol%. Moreover, the internal quantum yield of practical down-conversion was determined by integrating sphere to be ∼15.32% under excited by 320 nm light. The optically thermal stability was studied by the temperature dependence emission spectra, and the result showed that as the ambient temperature increases from 293 K to 423 K, the integrated emission intensity remains around 89%. Therefore, the prepared single crystal is a promising optical device material at present.