Intense upconversion luminescence is reported for the first time in a Ho3+-doped nanocrystalline material. Anti-Stokes blue and green luminescence was noted in nanocrystalline Gd3Ga5O2:Ho3+ after excitation into the F-5(5) level with 647 nm radiation. Excitation at 756 nm into the I-5(4) level resulted in green and red anti-Stokes emission. In both cases, an excited state adsorption mechanism is thought responsible for the observed upconversion luminescence. The temporal dependence of the upconverted luminescence for the two excitation wavelengths revealed that the I-5(7) level was the intermediate level in both two-photon processes.
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