Original KGd2F7 nanocrystals in fluoro-oxide glass ceramics by Dy3+/Sm3+ co-doped for white light emission

Serial fluoro-oxide glass ceramics (GCs) containing 0.6 mol% Dy ³⁺ and various Sm ³⁺ from 0 mol% to 1.5 mol% co-doped novel KGd ₂F ₇ nanocrystals were firstly fabricated through high temperature melt-quenching method. Then the microscopic structure of the GCs was revealed by transmission electron microscopy (TEM). And the rare-earth ions (RE ³⁺) of Dy ³⁺ and Sm ³⁺ were successfully doped in monoclinic-phase KGd ₂F ₇ nanocrystals, which can be verified by energy-dispersive X-ray spectroscopy (EDX) mappings. The photoluminescence spectra of the GCs were probed systematically utilizing 365 nm excitation light. The yellow (573 nm), green (486 nm), and red (648 nm) multiple emissions were observed in the co-doped GCs, and the intensity of red became stronger because of the higher Sm ³⁺ doping concentrations. This contribution of multiple emissions is due to the co-absorption of both Dy ³⁺ and Sm ³⁺ for 365 nm and the presence of energy transfer (ET). Moreover, the ET between Dy ³⁺ and Sm ³⁺ was confirmed from the variations of emission spectra and measured decay curves of emissions. Furthermore, the maximum energy transfer efficiency (ETE) from Dy ³⁺ to Sm ³⁺ can reach ~60.34% and the internal quantum yield (QY) is computed to be around 31.82% upon excitation of 365 nm. The chromaticity coordinates (CIE (Commission Internationale de L′Eclairage)− 1931) of the GCs can be tuned effectively through changing activator concentrations. Ideal white light emission is at the CIE (0.3357, 0.3342), which was achieved for 0.6 mol% Dy ³⁺/0.9 mol% Sm ³⁺ doped GCs sample. The results indicated that Dy ³⁺/Sm ³⁺ co-doped GCs with both high thermal and chemical-physical stabilities have strong potential application in white light-emitting diodes and fluorescent display devices.