This collection of papers describes investigations of luminescence centers in II-VI crystal phosphors, ruby, and molecular crystals. These investigations were carried out using spec- troscopy in a wide range of wavelengths, electron paramagnetic resonance, and polarization methods. The relationship between the thermal and optical depths of electron traps is con- sidered specifically. The articles in this collection should be of interest to all scientists investigating the luminescence of solids. v CONTENTS Investigation of the Spectral-Luminescence Properties of Ruby as Active Laser Medium V. B. Neustruev Introduction ****. *** 1 Chapter I. Spectral Distribution of Luminescence Quantum Efficiency and Absorption Spectra . **. " * * * * . * * * * * * * . * * * * * * * * * * * * * * * * * * * * * * * 5 Chapter II. Phosphorescence of Ruby. Energy Band Scheme. * * * . * * * . * . * * * * * 12 Chapter III. Color Centers in Ruby. * * * . * * * * * * * * * * * * * * * * * * * * * * * * * * * . 16 Chapter IV.