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

Abstract

This article analyzes up-conversion physical processes under CW laser excitation. A qualitative `population branching ratio β' 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.