Effect of Photoelectron Traps on X-ray Induced Luminescence of Y2O3 Polycrystals Sintered from the Nanopowder

It has been shown recently, that under X-ray long-term irradiation the luminescence intensity of polycrystalline samples of yttrium oxide in the light emission band associated with self-trapped exciton pairs of electrons and holes, decreased essentially with a time. For X-rays with 50 keV photon energy, which were used in the luminescence experiments, the main mechanism of interaction of the radiation with matter is photoelectric effect. The developed quantitative model of the luminescence is based on the assumption that some of the high-energy photoelectrons can be captured by intergrain caverns as natural traps. It means that the source of high-energy primary photoelectrons can be divided into two parts, one of which describes the source power of photoelectrons which will be captured and another describes photoelectrons responsible for the formation of self-trapped excitons. The probability of nonexcitonic relaxation is directly proportional to the concentration of captured high-energy electrons. As a result, the fraction of photoelectrons involved in the exciton formation decreases as the concentration of captured electrons increases with time. According to the proposed model, the decrease over time of the fraction of electrons involved in exciton formation leads to the exponential damping of the luminescence intensity, which is in a good agreement with the experimental data. The degree of photoelectron trap influence on the decrease of the luminescence intensity with time depends on the ratio of the total volume of intergrain caverns to the total volume of the polycrystalline sample and on the projected path length of high-energy photoelectrons.