Phototropic centers in lasers systems based on rare earth garnet crystals

The emission from Cr³⁺ ions at 730 nm is enhanced under the action of the second harmonic radiation of a neodymium laser, while the intensity of emission at 1.54 μm from Cr⁴⁺ ions in tetrahedral positions remains unchanged. This result casts doubt on the interpretation of absorption bands at 0.775–1.26 μm and the luminescence bands at 1.103–1.67 μm in the spectra of rare earth garnets, which have been previously assigned to electron transitions in Cr⁴⁺ ions occupying tetrahedral positions in the garnet structure.