Anomalous fast luminescence of CsСеSiS$_4$ thiosilicate

CsСеSiS$_4$ thiosilicate single crystals were obtained by high-temperature flux synthesis. The absorption spectrum in the region of 450 nm is formed by $f\to d$ transitions in the Ce$^{3+}$ ion. The nonelementary $5d\to 4f$ band of Ce$^{3+}$ ion emission is observed in the photo- and X-ray excited luminescence spectra in the region of 520 nm at temperatures of 5–330 K. The inertialess luminescence decay kinetics upon excitation by X-ray synchrotron radiation is characterized by a dominant component with a decay time $\tau$ = 0.88 ns. The luminescence of Ce$^{3+}$ ions is efficiently excited by the intracenter way or due to the recombination of band charge carriers.