Cr3+Fluorescence in Garnets and Other Crystals

The results of a study of the sharp-line fluorescence of ${\mathrm{Cr}}^{3+}$ in a number of crystals is presented. The host crystals were several diamagnetic garnets, a spinel, and emerald. The results are used to discuss two aspects of the sharp-line energy levels. First, some of the dynamical aspects are considered. The measurements of the temperature dependence of the sharp no-phonon $R$-line positions, linewidths, and efficiencies are in reasonable agreement with the existing theory. The theory assumes a simple form for the interaction of the ${\mathrm{Cr}}^{3+}$ energy levels with the phonons and uses a Debye density of states. The phonon-assisted radiation is also discussed. Second, some of the static aspects of the energy levels are considered. The splittings between the no-phonon $R$ lines along with splittings of the ground states of the ${\mathrm{Cr}}^{3+}$ in the same crystals are compared with the predictions of existing theories. Here the agreement is very poor. The experimental data show the difference between the ${\mathrm{Cr}}^{3+}$ energy levels, when odd terms in addition to usual even crystal-field terms exist. The data also indicate some large nonlinearities between the energy-level splittings and the crystal field.