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 Lu3xY3-3xAl5O12 (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)A2) 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 C3i 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.