Intense UV upconversion through highly sensitized NaRF4:Tm (R:Y,Yb) crystals

Abstract

Photon upconverting luminescent hexagonal NaRF₄:Tm (0.5 mol%) (R:Y³⁺,Yb³⁺) crystals with Yb³⁺ concentrations between 20 and 99.5 mol% were synthesized by a modified thermal coprecipitation method. The effects of the Yb³⁺ sensitizer concentration on the shape, size, structure, upconversion luminescence intensities and dynamic luminescence lifetimes were studied in detail. The intensity of ultraviolet upconversion luminescence at 340–365 nm upon 980 nm excitation increased up to 20 times with increasing Yb³⁺ concentration. The mechanisms for the changes in morphology, size and UV upconversion emission are discussed. In addition, the effect of the Tm³⁺ concentration on the UV emission of NaYbF₄ crystals was investigated. The results demonstrate that the NaYbF₄ with Tm³⁺ concentration between 0.4 to 0.8 mol% produce the most intense UV upconversion luminescence. These crystals may find applications in e.g. UV-visible solid state lasers or as an internal UV radiation source for many photochemical reactions.