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Blue up-conversion fluorescence from the Tm 3؉ : 1 G 4 → 3 H 6 efficiency of the energy transfer to Tm 3ϩ . Zou and Toratani 12 investigated the dynamics and mechanism of the energy transfer (480 nm) transition has been observed from calcium aluminate glass codoped with Tm 3؉ /Nd 3؉ . The mechanism for the between Tm 3ϩ and Yb 3ϩ by exciting Yb 3ϩ with a pump light that has a wavelength () of 980 nm. They suggested that the up-conversion process consists of a two-photon process. An excitation beam with a wavelength of 791 nm first energy-transfer mechanism was such that the pump photon was first absorbed by Yb 3ϩ via the 2 F 7/2 → 2 F 5/2 transition. Then, the excites Tm 3؉ to the 3 H 4 level, where Tm 3؉ again absorbs the 1060 nm emission from Nd 3؉ : 4 F 3/2 → 4 I 11/2 to attain the energy was transferred to the Tm 3ϩ : 3 H 5 level first and attained the Tm 3ϩ : 1 G 4 level after a series of multiphonon relaxation Tm 3؉ : 1 G 4 level. Lifetime and intensity variations with compositions suggest the presence of an efficient energy transfer and reabsorption of the emissions from the Yb 3ϩ : 2 F 5/2 → 2 F 7/2 from Nd 3؉ to Tm 3؉ . The highest 480 nm emission intensity transition. A similar mechanism also was suggested previously has been obtained from the glass with 0.1 mol% of Nd 2 O 3 by Bennett et al. 9 The overall energy transfer procedure conand 0.2 mol% of Tm 2 O 3 .sisted of a three-photon process with a diffusion-limited energy transfer 12 from Yb 3ϩ to Tm 3ϩ . Blue up-conversion in these systems was achieved mainly by using pumping sources

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Emission properties of 2.0 m fluorescence and the energy transfer between Ho 3؉ and Tm 3؉ in 57PbO⅐25Bi 2 O 3 ⅐18Ga 2 O 3 (mol%) glass codoped with Ho 3؉ and Tm 3؉ were investigated. Cross-relaxation rates in Tm 3؉ increased approximately 5 times when the Tm 2 O 3 concentration was increased from 1.0 to 1.5 wt%. Coefficients of the forward Tm 3؉ 3 Ho 3؉ energy transfer were about 15 times larger than those of the Tm 3؉ 4 Ho 3؉ backward transfer. Analysis of the energy transfer and gain spectra indicated that the highest gain at the 2.0 m wavelength region could be achieved from the glass with 1.5 wt% of Tm 2 O 3 and 0.3 wt% of Ho 2 O 3 .