Optical spectra of undoped and rare-earth-(=Pr, Nd, Eu, and Er) doped transparent ceramic Y3Al5O12

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Abstract
Undoped and rare‐earth‐ (Pr, Nd, Eu, and Er) doped transparent Y3Al5O12 ceramics have been prepared, and their optical spectra have been measured. It is found that absorption coefficient of the undoped ceramic Y3Al5O12 is almost independent of wavelength with 0.258 cm−1, which gives transmittance of the undoped ceramic Y3Al5O12 to be, for example, 95% for a 2‐mm height. Peaks in the absorption and emission spectra of Pr:Y3Al5O12 are assigned to the transitions in 4f2 configuration. The transitions from the multiplets with total angular momentum J=0 to multiplets with even J momentum are strong as predicted by Judd–Ofelt theory. The overall and detail structure of the absorption and emission spectra of Nd:Y3Al5O12 is the same as those in a previous publication. However, the absorption coefficient at nonabsorbing wavelengths by Nd3+ is reduced from more than 1.7 to 0.25 cm−1. A simple estimation of the population inversion threshold of the Nd:Y3Al5O12 ceramic reveals that the threshold is still about 25 times larger than that of single‐crystal Nd:Y3Al5O12. Peaks in the absorption and emission spectra of Er:Y3Al5O12 ceramic are assigned to the transitions in 4f11 configuration. The transition energies agree well with those reported for single‐crystal Er:Y3Al5O12 and the other hosts within 30 cm−1. A Stark splitting scheme for some multiplets has been constructed. Peaks in the emission, absorption, and excitation spectra of Eu:Y3Al5O12 ceramic are assigned to the transitions in 4f6 configuration. The transition energies are in very good agreement with those of single‐crystal Eu:Y3Al5O12 within 8 cm−1 for the emission peaks and 3 cm−1 for the absorption and excitation peaks. Spectral characteristics and derivation of a broad peak in the absorption spectrum at around 280 nm are discussed in some detail.