Development of a model for evaluating the luminescence intensity of phosphors based on the PHITS track-structure simulation

Abstract

Radiation-induced phosphors are frequently used as radiation detectors to measure dose distributions of swift ions. However, the luminescence intensity per dose of the phosphor at the Bragg peak regions decreases because of the quenching effects. To precisely measure the dose distribution for various radiation types using phosphor detectors, understanding the mechanism of quenching effects, induced by the electrons at the atomic scale, is crucial. In this study, we developed a new microdosimetric model for evaluating the luminescence intensity of phosphors based on the track-structure (TS) modes applicable to arbitrary materials implemented in the Particle and Heavy Ion Transport code System (PHITS). Herein, the two dominant factors for determining the luminescence intensity, such as (1) the energy required to generate an electron-hole pair and (2) their transfer efficiency to the luminescence center, are estimated from the TS mode in PHITS by calculating the number of stopped electrons and their spatial distributions. Using the developed model, we calculated the energy required to generate an electron-hole pair in various phosphors, which revealed a complex dependency on the bandgap energy, the composition, and the density of the material. Furthermore, we simulated the quenching effects of the BaFBr detector by calculating its transfer efficiencies for swift-ion irradiation and compared the simulation results with the corresponding experimental data. The comparison suggested that the density of luminescence centers is an essential parameter of the phosphors to reproduce the experimental quenching effects. The developed model is based on the first-principles calculation without any empirical correction; therefore, it is expected to contribute widely to developing phosphor detectors.