3d and 4f Ions in Solids: Description and Understanding of Optical Properties

An overview of recent results on modeling of properties of optical materials doped with transition metal and rare earth ions is given. Studies of various groups of materials – pyrochlores, perovskites, garnets, spinels – are presented. Applications of several different approaches (e.g. crystal field theory, DFT-based computational techniques, configurational coordinate model etc) are discussed in details. Special attention is given to the positioning of impurity ions energy levels in the host band gap. It is shown that through the combination of the crystal field theory and ab initio methods of electronic structure calculations it is possible to build up the complete energy level scheme of a doped crystal, which includes the host’s electronic band structure and impurity ion energy levels superimposed onto it.

A new model that links together the energies of the spin-forbidden transitions of transition metal ions (Mn⁴⁺, Cr³⁺, Ni²⁺) with the covalent effects experienced by those ions is also outlined. Several recommendations on how to tune the emission wavelengths of the Mn^{4+ 2}E_g – ⁴A_2g transition are outlined.

All shown examples are compared with the corresponding experimental results (whenever possible). Predictive potential of the presented models is discussed.