A tetragonal La²⁺ center (symmetry C_4v) was identified in single crystals of BaFCl and SrFCl doped with lanthanum with the aid of electron paramagnetic resonance (EPR)/electron-nuclear double resonance (ENDOR). This center forms a donor-acceptor couple with initially present F(F^-) centers. Switching takes place by illumination of appropriate wavelength. The kinetics of the process was monitored by EPR as La²⁺ and the unswitched F center are paramagnetic. The results of our experimental investigation of this kinetics are presented. A foregoing spectroscopic characterization of the La²⁺ center allowed one to identify a d-d (the B₁-E) transition, a charge-transfer band (for BaFCl at 10940cm^-1 and at 17890cm^-1, respectively) and to obtain a value of 710cm^-1 for the spin-orbit coupling constant in the ground state. In order to narrow the choice of possible acceptor-donor partners a detailed EPR/optical search was further done to identify a number of lattice defects and oxygen centers—in addition to a La-oxygen molecular structure.

The vibrational spectra of some 1,2,4-trioxanes present two characteristic bands at 790 and 880 cm^−1. On the basis of ¹⁸O-isotopic substitution and comparison with analogous compounds, these bands have been assigned to coupled C—O and O—O stretching modes of the C—O—O element.

Single crystals of MoO₃ have been grown under an oxygen atmosphere using a horizontal tubular furnace. The temperature and pressure necessary to grow satisfactory crystals in oxygen along [100] and [010] directions are determined.