An initial basic physics model and comparative analysis for up-conversion sensitization luminescence

This article analyzes up-conversion physical processes under CW laser excitation. A qualitative 'population branching ratio beta' model is proposed for the first time. The physical understanding of up-conversion explored from this model can be deduced as the following five aspects. (1) The spontaneous emission rate A is a very important variable in determining the up-conversion efficiency. When the spontaneous emission rate A is smaller than the non-radiative relaxation rate W-n, i.e. A < W-n, the up-conversion efficiency increases with decrease of the phonon energy of host material. When A > W-n, the up-conversion efficiency increases with the increase of phonon energy. Past research has only studied the case of A < W-n. The significance and value of the A > W-n case has not been described previously. (3) A traditionally accepted concept, i.e. the up-conversion fluorescence of high cutoff phonon energy materials like quartz is about 10 000 times smaller than that of fluoride glass, is the result for case A < W-n. Therefore it is only partially description about the up-conversion process. (4) This paper also further proposes, for the first time, a phenomenological model 'equivalent spontaneous emission A(equivalent) to explore the particular physical significance of indirect up-conversion sensitization. Spontaneous emission A, together with other factors, could be considered phenomenological as an equivalent spontaneous emission A(equivalent). Generally A is small, however A(equivalent) is large. The range of up-conversion fluorescence increasing with the increase of phonon energy therefore could be expanded from W-n < A to W-n < A(equivalent). So that under indirect up-conversion sensitization, it is possible to obtain high up-conversion efficiency for material with large phonon energy such as oxyfluoride glass and so on. (5) Further study indicates that the optimized cutoff phonon energy should be in a range about between 600 cm(-1) and 900 cm(-1), and the host material should have large solubility for rare-earth ions in order to obtain a large indirect up-conversion sensitization fluorescence. This is of great significance for finding materials with both high up-conversion efficiency and advanced material properties to facilitate up-conversion development. As we know, the similar research has not been reported before. (C) 2000 Elsevier Science B.V. All rights reserved.