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

Luminescence offers a sensitive probe of the quality of Nd:YAG laser materi al both in the bulk and, via cathodoluminescence, in the near surface layer s. The spectral signals are primarily from the Nd dopants, but the thermolu minescence spectra reveal traces of impurities such as Tb, Cr and Mn. Contr ol 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 su rface dislocations and solvents from cleaning treatments. The effects are o ften apparent as discontinuities in the Nd signal intensities at temperatur es which match the solid-liquid or liquid-gas phase transitions of contamin ants. Additionally there is strong evidence for the inclusion of carbon dio xide, in the form of nanoparticles. At 202 K, the CO2 sublimation temperatu re, the Nd line intensities change discretely and there are wavelength shif ts for some of the emission lines consistent with pressure driven changes i n the lattice parameter. Data for x-ray lattice parameters identify a compl ex acid sudden change and expansion of the lattice in this temperature regi on. The luminescence methods used suggest identification of impurities and gaseous inclusions can be exploited in other insulator materials and exampl es are cited.