Photoluminescence and afterglow kinetics of ZnSe(Te,O) single crystals with radiation defects

Crystals and films of chalcogenides are considered as perspective material for photosensitive heterostructures and blue-green light emitters. However, it is necessary to solve the problem of radiation stability of crystal structure and optical characteristics. We studied ZnSe (Te) single crystals synthesized at the concern with subsequent thermal treatment in oxygen and Zn vapor for modifying the surface structure, and then irradiated with ∼1.25 MeV gamma-rays to the dose of 108 R and 18 MeV protons to the fluence of 1015 cm-2 at 320 K for generation of different defects. The content of Te in A-series of samples was ∼0.5 and ∼0.25 %. Samples treated in oxygen contained ∼0.2 % Te (B series) and <0.01 % Te (C series). Spectral and kinetic characteristics of photoluminescence (PL) and afterglow (AG) were studied at 300 K and the set-up comprising nitrogen pulse laser (337 nm, 12 ns), optical monochromator with photoelectric registration, and stroboscope with the apparatus function of 5 ns. PL spectra were dominated with a wide band at 600 nm (C-series) or 620 nm (A, B series). The more Te concentration was, the weaker the PL was. The AG time was < 5 μc, < 20 μc, and < 1 μc in A-, B- and C-samples, which is much shorter that that for NaI(Tl)∼1000 μc. Shallow O-centers are responsible for fast recombination, and pair Te-O-centers give rise to much slower recombination. Treatment in Zn-vapor resulted in enhancement of PL at 620 nm and slowing down of AG to 60 μc in Te-doped samples (A and B series), i.e. the main optical centers involved Te. Gamma-irradiation not only suppressed PL, but also resulted in appearing new luminescent centers emitting at 500 nm, which can be attributed to generated close Frenkel defect pairs near Te impurity. Besides, the AG time became much shorter in A- and B-series, while just the opposite effect occurred in C-series. Samples treated in Zn-vapor turned out quite stable to gamma-irradiation. Irradiation with protons caused similar changes in PL spectra, although the effect of AG shortening turned out more significant, especially in the proton beam range. Clear difference was found between the optical responses from the area of proton beam path, non-irradiated frontal part and back surfaces due to the induced structure defects and surface damage at radiolytic mass losses. Thus, one can conclude, that the intensive ionizing irradiation generates Frenkel defect pairs in ZnSe crystal lattice, i.e. vacancy-interstitial, some of them being optically active. Radiative charge recombination at these pairs is responsible for the fast red PL. Stabilization of such pairs near Te impurity ions gives rise to the green band at 500 nm. The irradiation induced shortening the afterglow at the same intensity of photoluminescence is interesting for producing stable fast emitters in visible range