The photoluminescence spectra of Al 2 O 3 : Cr 3 nanopowder under excitation by a frequencydoubled YAG:Nd laser (l ex 532 nm) and a nitrogen-vapour pulsed laser (l ex 337:1 nm) have been studied. A considerable difference between the spectra of nanocrystalline and macrocrystalline samples has been observed. The nanocrystalline samples reveal a broad asymmetric line with the maximum at 690 nm under the YAG : Nd excitation, whereas under the nitrogen-vapour laser excitation, the broad line becomes more symmetric, and its maximum shifts by 45 nm to the longer-wavelength region. The above shift is shown to be due to a drastic change in the HuangRhys parameter of the 2 E± 4 A 2 transition. A decay of the broad line with the increase of the duration of UV illumination has been observed.
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