Effect of composition on the structure, spontaneous and stimulated emission probabilities of various 1.0 mol% Tm 2 O 3 doped (1Àx)TeO 2 +(x)WO 3 glasses were investigated using Raman spectroscopy, ultraviolet-visible-nearinfrared (UV/VIS/NIR) absorption and luminescence measurements.Absorption measurements in the UV/VIS/NIR region were used to determine spontaneous emission probabilities for the 4f-4f transitions of Tm 3+ ions. Six absorption bands corresponding to the absorption of the 1 G 4 , 3 F 2 , 3 F 3 and 3 F 4 , 3 H 5 and 3 H 4 levels from the 3 H 6 ground level were observed. Integrated absorption cross-section of each band except that of 3 H 5 level was found to vary with the glass composition. Luminescence spectra of the samples were measured upon 457.9 nm excitation. Three emission bands centered at 476 nm ( 1 G 4 -3 H 6 transition), 651 nm ( 1 G 4 -3 H 4 transition) and 800 nm ( 1 G 4 -3 H 5 transition) were observed. Spontaneous emission cross-sections together with the luminescence spectra measured upon 457.9 nm excitation were used to determine the stimulated emission cross-sections of these emissions.The effect of glass composition on the Judd-Ofelt parameters and therefore on the spontaneous and the stimulated emission cross-sections for the metastable levels of Tm 3+ ions were discussed in detail. The effect of temperature on the stimulated emission cross-sections for the emissions observed upon 457.9 nm excitation was also discussed. r
The capture and emission dynamics of deep levels in GaAs/Ga1−xAlxAs multiple quantum well structures are investigated by using the photoinduced transient spectroscopy technique. In nominally undoped samples three trapping levels with activation energies in the range between 0.4 and 0.8 eV are observed. These are compared with the observations based on other conventional techniques. Large capture cross sections associated with the trapping centers implies that the presence of these can be detrimental for the high speed operation of optoelectronic devices based on GaAs/Ga1−xAlxAs quantum well structures.
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