Anomalous discrete disorder response of high-symmetry impurity centers spectra in garnet solid solutions

The zero-phonon electronic transitions in Cr 3+ and Ce 3+ impurity ions in a series of Lu 3 x Y 3−3 x Al 5 O 12 (0 < x < 1) garnet solid solution crystals were studied experimentally. It was observed that in contrast to the case of Ce 3+ , the modification of zero-phonon R-line ( 2 E- 4 A 2 ) fluorescence spectra of Cr 3+ ions with changing x occurs in a discrete fashion and is not accompanied by strong inhomogeneous broadening, as usually happens in solid solutions. The effect is ascribed to the high C 3i symmetry of the Cr 3+ (Al 3+ ) sites that allows only a limited number of non-equivalent Cr 3+ centers in a mixed environment. The energies and radiative lifetimes of the 2 E states of locally identical Cr 3+ centers inside different mixed garnet matrices were studied and the observed dependences on the Lu content x are discussed in terms of lattice compression and dilation. The zero-phonon line spectrum of Cr 3+ ions in Lu 3 x Y 3−3 x Al 5 O 12 crystals changes with x discretely rather than continuously.