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

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 ((5)G(2) -> I-5(8)), 391 (K-3(7) -> I-5(8)), 412 ((5)G(4) -> I-5(8)), and 446 nm ((5)G(5) -> I-5(8)). 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 S-5(2) and (5)G(3) (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+.