Excited-state absorption mechanisms in red-laser-pumped uv and blue upconversions in Tm3+-doped fluoroaluminate glass.

The mechanism of red-pumped frequency-upconversion fluorescence observed in the uv and blue ranges of frequencies for a Tm 3+ -doped fluoroaluminate glass was investigated by single-wavelength pumping of a tunable 4-(dicyanomethylene)-2-methyl-6-(p-dimethyl-amino-styryl)-4H-pyran dye laser. It was found that the dependences of fluorescence intensity on the incident excitation power were quadratic both for the 0.36- and 0.45-μm emissions, which originate from 1 D 2 , and for the 0.48-μm emission from 1 G 4 , indicating two-step excitation mechanisms