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Optical absorption curves for nominally pure and Ce 3+ doped single crystals of Y 3 Al 5 O 12 (YAG) have been measured in the region of 5 eV–7 eV at 292 K, 78 K and 10 K. The parameters of the Urbach rule have been determined referring to those optical absorption curves which are believed to be the fundamental absorption tail of YAG single crystals at these temperatures, respectively. Optical absorption measurements on single crystals of YAG:Nd 3+ (the concentration [Nd 3+ ] L being 0.60 atm.%) have disclosed strong absorption spectra consisting of at least five Gaussian bands in the region of 5.0 eV–7.0 eV at 292 K and 78 K. These spectra have been interpreted to originate from the interconfigurational transitions 4 f 3 →4 f 2 5 d of Nd 3+ in YAG.

The absorption spectra due to the 4 f →5 d transitions in Ce 3+ centres have been measured with the use of YAG:Ce 3+ single crystals with a lattice concentration [Ce 3+ ] L =(1.28±0.05)%. The data are almost independent of the spectral behaviour of a reference spectrum whose absorption constants are ∼2 cm -1 at the highest, since the absorption constants of 129 cm -1 and 50 cm -1 have been derived, relative to the reference spectrum, at the strongest peaks in the dγ and d e regions, respectively. The absorption area 32.3 cm -1 eV measured on the strongest dγ-band suggests that about a quarter of the Ce-concentration, [Ce 3+ ] M , added in the mixture of the starting powders is incorporated into [Ce 3+ ] L as YAG:Ce 3+ . It is found that the highest-energy lying d e band is located at 6.06 eV, in agreement with 6.07 0 eV for the corresponding band peak in the excitation spectrum and that the ratio of the absorption area of dγ to that of d e is nearly 2:3.