Infrared-to-visible upconversion emission enhancement through thermal effects in Yb 3ϩ -sensitized Pr 3ϩ -doped fluoroindate glasses excited at 1.064 m is investigated. A twentyfold increase in the 485 nm blue emission intensity as the sample temperature was varied from 20 to 260°C was observed. The visible upconversion fluorescence enhancement is ascribed to the temperature dependent multiphonon-assisted anti-Stokes excitation of the ytterbium sensitizer and excited-state absorption of the

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... eodymium acceptor. A model based upon conventional rate equations considering a temperature dependent effective absorption cross section for the 2 F 7/2 → 2 F 5/2 transition of the Yb 3ϩ and 1 G 4 → 3 P 0 excited-state absorption of the Pr 3ϩ , agrees very well with the experimental results.