The influence of nanoparticle sizes on the X-ray excited luminescence intensity in YVO4:Eu

Abstract

The experimental dependence of the luminescence intensity of YVO4:Eu nanoparticles on their size in the range from 8 to 16 nm is studied. It has been shown that the decrease of the X-ray excited luminescence intensity with the decreasing size of the nanoparticle is caused both by quenching resulting from the interaction of luminescent centres with surface defects and by losses of excitation energy at the stage of thermalisation. A method of calculating the dependence of the X-ray excited luminescence intensity on the nanoparticle size is proposed based on the assumption that only the charge carries not reaching the near-surface layer of particle after the thermalization process give contribution to the recombination luminescence. The length of thermalisation was calculated taking into account the dependence of the effective mass of electrons on their kinetic energy. The average value of the effective mass of electrons in the conduction band with the kinetic energy in the range [0, Eg] is estimated to be 1,5me. The distribution of secondary electrons by the thermalisation lengths for YVO4 is obtained and its average value is estimated to be 6 nm. The minimum size of YVO4 nanoparticles possessing the intensity of X-ray excited luminescence approximately twice smaller comparing to the bulk crystal is theoretically estimated to be 27 nm. This value is significantly smaller than any visible light wavelengths that minimize all processes of light scattering and it gives an opportunity to create composite polymer-inorganic materials based on these nanoparticles for X-ray registration.