Growth and optical properties of the solution-melt K$_2$O $\times$ 8Ga$_2$O$_3$ crystals

The results of studying the crystallographic, electrical and optical properties of K$_2$O $\times$ 8Ga$_2$O$_3$ crystals obtained by interaction of a Ga$_2$O$_3$ solution with a KF melt are presented. The crystal structure of the samples corresponded to hexagonal $P6_3$/mmc $\beta$-gallate with the lattice parameters $a$ = 5.80 $\mathring{\mathrm{A}}$ and $c$ = 23.5 $\mathring{\mathrm{A}}$. The crystals were insulators with a resistance of about 2–3 G$\Omega$ per 450 $\mu$m of length. For the first time, the optical band gap of 3.77 eV and the intrinsic luminescence band in the range of 2.0 – 2.5 eV were determined for K$_2$O $\times$ 8Ga$_2$O$_3$.