Low temperature luminescence from the near surface region of Nd:YAG

Luminescence offers a sensitive probe of the quality of Nd:YAG laser material both in the bulk and, via cathodoluminescence, in the near surface layers. The spectral signals are primarily from the Nd dopants, but the thermoluminescence spectra reveal traces of impurities such as Tb, Cr and Mn. Control of the electron energy of the cathodoluminescence demonstrates that the outer few micron layers differ significantly in luminescence response from the bulk crystal. The cathodoluminescence signals are influenced by near surface dislocations and solvents from cleaning treatments. The effects are often apparent as discontinuities in the Nd signal intensities at temperatures which match the solid-liquid or liquid-gas phase transitions of contaminants. Additionally there is strong evidence for the inclusion of carbon dioxide, in the form of nanoparticles. At 202 K, the CO2 sublimation temperature, the Nd line intensities change discretely and there are wavelength shifts for some of the emission lines consistent with pressure driven changes in the lattice parameter. Data for x-ray lattice parameters identify a complex acid sudden change and expansion of the lattice in this temperature region. The luminescence methods used suggest identification of impurities and gaseous inclusions can be exploited in other insulator materials and examples are cited.