Abstract

This thesis presents an extensive spectroscopic investigation of Er$\sp{3+}$ doped in YVO$\sb4$ single crystals. The polarized visible and near infrared absorption and emission spectra are presented. The spectra were analyzed to determine the energy levels of Er$\sp{3+}$ in YVO$\sb4$ and a complete energy level scheme for the 4f$\sp{11}$ ground configuration of Er$\sp{3+}$ was determined. A total of 59 crystal field levels were observed of the 70 predicted to split out in D$\sb{\rm 2d}$ symmetry. The experimental Stark level energies were used as input in data in a parameterized Hamiltonian to calculate the crystal field parameters. Judd-Ofelt theory was applied to the polarization-averaged room temperature optical-absorption spectra to predict the crystal intensity parameters; $\Omega\sb2,\ \Omega\sb4,$ and $\Omega\sb6,$ the radiative decay rates and branching ratios for the Er$\sp{3+}$ transitions from the various excited states to the lower level J-manifolds. Thermalization of the $\sp2$H$\sb{1 1/2}$ level from the lower lying $\sp4$S$\sb{3/2}$ was studied. The upconversion of red (652.7 nm) and near infrared (799.1 and 979 nm) radiation into green (due to the $\rm{\sp4S\sb{3/2}}\to{\sp4I\sb{5/2}}$ and the thermally populated $\rm{\sp2H\sb{11/12}}\to{\sp4I\sb{15/2}}$ transitions) and red (due to the $\rm{\sp4F\sb{9/2}}\to{\sp4I\sb{5/2}}$ transition) emission has been studied for Er$\sp{3+}$ ions in YVO$\sb4$ single crystals over a wide temperature range and several dopant concentrations. The upconversion pathways and dynamics for all three excitations were studied. Sequential absorption of photons, energy transfer, and cross-relaxation energy transfer upconversion processes were found to be active and could be identified on the basis of the upconversion transients. An analysis of the upconversion transients shows that energy migration dominates at higher concentrations of Er$\sp{3+}$ (10%). An extensive investigation of the fluorescence dynamics of the $\rm\sp4S\sb{3/2},\ \sp4F\sb{9/2},\ \sp4I\sb{9/2},\ \sp4I\sb{11/2},$ and $\rm\sp4I\sb{13/2}$ states was carried. The decay profiles the luminescence of the $\rm\sp4S\sb{3/2}$ level of Er$\sp{3+}$ (1.0%) obey the Inokuti-Hirayama model for energy transfer for an electric dipole-electric dipole interaction, in the absence of diffusion among the donors. The dipole-dipole coupling parameter was estimated to be $2.9\times 10\sp{-51}$ m$\sp6$s$\sp{-1}$ and compared well to other well known systems.