Optical Absorption of Single Crystals of Y_3Al_5O_12 and Y_3Al_5O_12:Nd^3+ in the UV Fundamental Absorption Edge Region

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Optical absorption curves for nominally pure and Ce³⁺ doped single crystals of Y₃Al₅O₁₂ (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:Nd³⁺ (the concentration [Nd³⁺]_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 4f³→ 4f²5d of Nd³⁺ in YAG.