Time-resolved photoluminescence of LaBr$_3$:Ce scintillation crystals under ultrasoft X-ray excitation

Time-resolved X-ray-induced photoluminescence (PL) of LaBr$_3$:Ce scintillation spectrometer crystals excited by synchrotron radiation with photon energies within 45–290 eV has been studied at 7.5 and 295 K. It is established that the PL response is essentially nonproportional to the exciting photon energy in the regions of photoionization of the Br $3d$ and La $4d$ levels and especially in the vicinity of the giant resonance. The PL decay kinetics in the spectral region corresponding to the $d\to f$ luminescence of Ce$^{3+}$ ions is nonexponential. The decay time is smaller than 15 ns and depends on the exciting photon energy and radiation wavelength. The influence of the products of interaction of these hygroscopic crystals with atmosphere on the spectral and kinetic characteristics of X-ray-induced PL has been determined.