Upconversion in Ho³⁺-doped YbF₃ particle prepared by coprecipitation method

Abstract

YbF₃ particles doped with Ho³⁺ were synthesized by coprecipitation method, from which the ultraviolet and visible emission bands of the Ho³⁺ and the 480 nm cooperative upconversion emission of Yb³⁺–Yb³⁺ are observed under 980 nm excitation. Under the same excitation power, the emission intensity of Ho³⁺ in coprecipitation method is enhanced by about two times comparing to that in solid-state reaction method. The novel ultraviolet and violet emissions of the Ho³⁺ are firstly obtained which are centered at 360 (⁵G₂→⁵I₈),391 (³K₇→⁵I₈),412 (⁵G₄→⁵I₈), and 446 nm (⁵G₅→⁵I₈). The luminescence decay profiles of 545 and 652 nm visible emissions were obtained with a 980 nm pulsed laser. The excitation power dependence of the emission intensity was also measured and intensity saturation was observed. Based on the level structures of Ho³⁺, two- and three-photon processes are suggested to perform populations of ⁵S₂ and ⁵G₃ (Ho³⁺) levels, respectively. The dominant upconversion mechanism may be attributed to a cooperative sensitization process of two excited states of Yb³⁺ and energy transfers from Yb³⁺ to Ho³⁺.