Thermophysical properties of lithium thiogallate that are important for optical applications

Alexey Kurus; Alexander Yelisseyev; Sergei Lobanov; Pavel Plyusnin; Maxim Molokeev; Leonid Solovyev; Dmitry Samoshkin; Sergei Stankus; Svetlana Melnikova; Lyudmila Isaenko

doi:10.1039/d1ra05698k

Thermophysical properties of lithium thiogallate that are important for optical applications

RSC Adv. 2021 Dec 8;11(62):39177-39187. doi: 10.1039/d1ra05698k. eCollection 2021 Dec 6.

Authors

Alexey Kurus^{1

2}, Alexander Yelisseyev^{1

2}, Sergei Lobanov^{1

2}, Pavel Plyusnin³, Maxim Molokeev^{4

5}, Leonid Solovyev⁶, Dmitry Samoshkin⁷, Sergei Stankus⁷, Svetlana Melnikova⁴, Lyudmila Isaenko^{1

2}

Affiliations

¹ Novosibirsk State University 2 Pirogov str. Novosibirsk 630090 Russia kurusaf@igm.nsc.ru.
² Sobolev Institute of Geology and Mineralogy SB RAS 3 Kopyug ave. Novosibirsk 630090 Russia.
³ Nikolaev Institute of Inorganic Chemistry SB RAS 3 Lavrentyev ave. Novosibirsk 630090 Russia.
⁴ Kirensky Institute of Physics SB RAS Krasnoyarsk 660036 Russia.
⁵ Siberian Federal University Krasnoyarsk 660041 Russia.
⁶ Institute of Chemistry and Chemical Technology SB RAS 42 K. Marx str. Krasnoyarsk 66049 Russia.
⁷ Kutateladze Institute of Thermophysics SB RAS 1 Lavrentyev ave. Novosibirsk 630090 Russia.

Abstract

Lithium thiogallate LiGaS₂ is one of the most common nonlinear crystals for mid-IR due to its extreme beam strength and wide transparency range; however, its thermophysical properties have not yet been practically studied. Large crystals of high optical quality are grown. DTA revealed features at 1224 K below melting point (1304 K) that are associated with the oxygen containing compounds of the LiGaO_2-x S _x type. The thermal conductivity of LiGaS₂ (about 10.05 W (m^-1 K^-1)) and band gap value (3.93 eV at 300 K) are found to be the highest in the LiBC₂ family. Isotropic points in the dispersion characteristics for the refractive index are found and LiGaS₂-based narrow-band optical filters, smoothly tunable with temperature changes, are demonstrated. Intense blue photoluminescence of anionic vacancies V _S is observed at room temperature after annealing LiGaS₂ in vacuum, whereas orange low-temperature emission is related to self-trapped excitons. When LiGaS₂ crystals are heated, spontaneous luminescence (pyroluminescence) takes place, or thermoluminescence after preliminary UV excitation; the parameters of traps of charge carriers are estimated. The obtained data confirm the high optical stability of this material and open up prospects for the creation of new optical devices based on LiGaS₂.