Abstract

Molecular complexes in solids have never been treated as possible laser materials. Among them are known luminophors and scintillators of pronounced luminescence over the range of some 150 nm and thus being potential candidates for tunable laser media (acting in blue-green region). In the few cases studied so far distinct excited state absorption (ESA), usually overlapping the luminescence and spreading even further, was observed. We have investigated C_aM_oC₄, C_aWO₄ (of nd⁰ electronic configuration) and Bi₄Ge₃O₁₂ (BGO) (ns² configuration). Interesting properties are displayed by BGO, where ESA increases with probe-beam intensity, the phenomenon being a sort of excited-state photochromism (ESP), possibly involving some trap levels in its mechanism. BGO has the best (smallest) ratio of ESA to stimulated emission crossections (^σESA/^σe) of about one order of magnitude (e.g., for 632.8nm^σESA ~ 4×10^–19cm²σ_e ~ 2×10^–20 cm²), which precludes a chance for lasing in this crystal. The two other crystals reveal rather "standard", broad ESA spectra of absorption crossections σ_ESA of the order of 10^–19, 10^–18 cm² whereas emission cross sections are ~ 10^–21, 10^–20 cm². The results, though precluding laser action in these materials, provide spectroscopic data, which, we believe, are new in the field of solid state optics.

© 1990 Optical Society of America