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+.