No abstract

LiGaS2 (LGS) is a recently developed nonlinear optical crystal widely used for nonlinear conversion in the mid-infrared spectral region, but its applications are significantly influenced by the native defects present in the lattice. In this work, absorption and photoluminescence (PL) spectra are studied after annealing the as-grown LGS crystal in different chemical environments in order to reveal features related to anion vacancy (VS) and cation antisite defect (GaLi). In addition, irradiation with fast electrons produces VS centers and their complexes in LGS. The VS migration and mutual transformations in these defects take place at room temperature whereas their complete annealing occurs at 670 K. Meanwhile, the first-principles calculations are adopted to identify the relevant optical transitions. A good agreement with the experimental results was obtained. It is established that the dominant defects VS result in the optical absorption at 3.43 eV and violet PL emission, while GaLi is responsible for absorption at 2.95 eV. The intense PL peak at 1.92 eV is associated with the self-trapped excitons in LGS. The other weak PL bands are also related to the recombination of electrons or holes with the VS and GaLi defect states.

Photoluminescence (PL) in two broad bands at 2.95 and 2.6 eV in lithium iodate α-LiIO 3 is associated with selftrapped excitons and native point defects (supposedly oxygen vacancies), respectively, based on the luminescence excitation spectra and the PL temperature dependence. Free charge carriers may be captured by two types of shallow traps with thermal activation energies of 0.14 and 0.21 eV: they are responsible for crystal darkening at temperatures below 200 K. Spontaneous emission of α-LiIO 3 during cooling or heating at temperatures T < 200 K is pyroluminescence, which occurs at dielectric breakdown in strong pyroelectric fields on the crystal surface and in its bulk as well as inside the channel defects.

The defect chalcopyrite crystal HgGa 2 S 4 has been employed in a 1064-nm pumped optical parametric oscillator to generate <7 ns long idler pulses near 6.3 µm with energies as high as 3 mJ, tunable in a broad spectral range from 4.5 to 9 µm.