ИСТИНА

Scintillators with efficient conversion of high-energy radiation into luminescence are needed for application in the new experiments in fundamental physics as well as in the medical imaging, new security control systems, etc. Compounds with NbO4 complex are characterized by the bright intrinsic luminescence in a wide temperature region, whereas the highest density can be achieved in compounds with TaO4 complex. It can be expected that RE(TaxNb1-x)O4 mixed crystals will combine the advantageous properties of both compounds. Another feature of mixed crystals is non-linear dependence of light output on the concentration of substituted ions. The enhancement of light output in the mixed crystals is usually observed [1], however the origin of the effect is still under discussion. The dependence of thermalization length of charge carriers on the composition of the mixed crystal is supposed to determine the light output in [2]. Here we present the study of the origin of the light output modification with x value of Y(TaxNb1-x)O4 mixed crystals. Samples of Y(TaxNb1-x)O4 with x=0, 0.2, 0.4, 0.6, 0.8, 1, have been synthesized by solid-state reaction. The luminescence characteristics of the samples were measured using synchrotron radiation at the branch-line FINEST at MAX-lab, Lund and using various laboratory set-ups under UV, VUV and X-ray excitation in the temperature region 10 – 400 K. The intrinsic emission observed in Y(TaxNb1-x)O4 is peaking at 2.8 eV and connected with excitons, self-trapped at NbO4 (x ≠ 1) or TaO4 (x = 1) groups. The dependence of light output on x demonstrate the increase of intensity for intermediate values of x in Y(TaxNb1-x)O4 at T = 300 K. Excitation spectra of exciton emission under vacuum ultraviolet excitation also show the increase of the probability of exciton creation for the intermediate values of x. The numerical simulation of exciton production under VUV excitation has been performed in order to demonstrate that the observed dependence of luminescence excitation spectra on x is determined by the modification of thermalization length. The modification of the bandgap with x value has been studied as well. The gradual shift of TSL peaks to lower temperatures with increase of x indicates the decrease of bandgap. This supposition is verified by the data of luminescence excitation spectra.