LAUSR

Abstract Low-temperature molten-salt method and the NH 4 NO 3 flux were developed to synthesize quasi-spherical cubic BaGdF 5 :Ce 3+ /Er 3+ /Yb 3+ nanocrystals with the average diameter of 30 nm. The optimum doping concentrations of Er 3+ and Yb 3+ are determined to 2 and 20 mol%, respectively. The introduction of Ce 3+ in BaGdF 5 : Er 3+ /Yb 3+ nanocrystals deduced a huge variation of the profile of the UC emission under 976 nm laser irradiation. The strong ultraviolet UC emission of 330–380 nm is due to the overlap of 4 G 7/2 , 2 K 15/2 , 4 G 9/2  →  4 I 15/2 transitions of Er 3+ , and strong blue one locating at 440–480 nm is attributed to the overlap of 4 F 3/2, 4 F 5/2  →  4 I 15/2 and 4 G 7/2 , 2 K 15/2 , 4 G 9/2  →  4 I 13/2 transitions of Er 3+ , respectively. The UC emission mechanism and energy transfer process of BaGdF 5 :Ce 3+ /Er 3+ /Yb 3+ nanocrystals were provided in detail and demonstrated by the fluorescence decay curves and pumping power dependent UC emission spectra. This work not only demonstrates a rational approach to tailor UC emission (red, blue and ultraviolet) by tuning doping ions and concentration, but also for better understanding of their essential UC luminescence properties.