Kinetics of photoluminescence of ZnSc(Te) scintillators under pulse laser excitation

Full text: A good scintillator for intensive radiation should have a fast response and negligible contribution from slow afterglow. The aim of this paper was to study both spectral and time characteristics of ZnSe single crystals doped with isovalent impurity of Te and before and after gamma-irradiation to the high dose of 109 R. The difference in the spectra of PL and the response time allows identify luminescent centers and suggest the composition of fast and effective scintillator. Nitrogen gas laser with the wavelength 337 nm and the pulse duration of 12 ns was used for inter-band excitation of photo-luminescence (PL) at 600-630 nm and also for measuring afterglow time relaxation. PL spectra were registered with spectrometer SPM-2 or monochromator MDR from 300 to 800 nm. The time resolution of scintillations of ZnSe(Te,O) samples from the pulse laser were measured with standard detector assembling based on the fast photomultiplier (FEU-30) having the apparatus function of 5 ns, fast stroboscope C7-8 (the time evolution ≥100 ps) and oscilloscope Tektronix 465 B (≥5 ns) Special care was taken to remove the glow of air from the detected signal. Given the exciting laser pulse of 12 ns, the fast component of PL pulse profile had the same width <20 ns. The time of afterglow - a slow tail at the level of 1 % of amplitude of the mam short pulse - varied from I to 150 μs. Such a surprisingly fast response of these crystals allows of suggesting the main contribution from hot exactions and free carriers exciting directly the red luminescence of intrinsic defects. Since the 337 nm laser quantum energy corresponds to the top of the first conductivity band, the lower laying excitons transfer their energy to the highest charged Zn-defect state on the bottom of the conductivity band exciting their luminescence. Stabilisation of luminescent centers with the impurity increases the light output but delays the afterglow to 80-150 μs Oxygen impurity was found to increase the intensity of PL and to shorten the afterglow to a few microseconds, which is much shorter than CsI(Tl). After the irradiation both the amplitude and duration of the response pulse did not change, however the PL, spectra did. The observed 'red shift' is due to the radiation induced luminescent center transformation in the presence of surplus of Zn atoms or VSe of 9·1020 cm-3 found in all studied samples