Study of closed-shell molecular complexes as possible laser media

We have evaluated a series of blue-green emitting molecular-complex materials (d⁰ electronic system) from the point of view of their suitability as possible tunable laser media. All of them reveal a very strong, broad-band excited-state absorption (ESA), occurring between states of different configurations and positioned at the energy related to the crystal field parameter 10 Dq. The ESA strongly overlaps the luminescence spectra. Because of the nature of the terminal state of ESA, the high rate of ESA transitions can be ascribed to the efficient breaking of the Laporte selection rule, because of considerable admixture of % orbitals of ligands and/or p-orbitals of the central ion into the d-orbitals of the central ion in the terminal configuration, and to the existence of triplet terms in this configuration. We survey the ESA characteristics and compare its cross sections to those of stimulated emission. We interpret the obtained results by means of a configuration-coordinate model. Some possible avenues of future work are indicated