Theoretical understanding of defects-driven mechanoluminescence for Pr3+-doped NaNbO3/LiNbO3 heterojunctions

Mechanoluminescence (ML), which involves the emission of light under mechanical stimuli, shows great potential in various applications such as sensing, imaging, and energy harvesting. Current research suggests that the luminescence mechanism of ML is typically connected to specific defects present within the material. In this study, we focus on the investigation of ML defects in Pr3+-doped NaNbO3/LiNbO3 heterojunctions, employing a combination of experimental and theoretical approaches. Through experimental analysis, we confirmed the presence of the heterojunction and its influence on ML intensity, and the optimal doping ratio for the heterojunction in ML was established. Furthermore, we examined the influence of varying Pr3+ doping concentrations on ML behavior and a proof-of-concept was demonstrated using the X-rays charged heterostructural phosphor as a stress sensor for biological applications. The position and concentration of internal defects in the ML material were scrutinized through thermoluminescence tests employing the variable heating rate method and positron annihilation. Complementing the experimental findings, theoretical simulations were conducted to elucidate the underlying mechanisms responsible for the observed ML defects. Density functional theory calculations were employed to investigate the energy levels, charge transfer processes, and lattice distortions within the heterojunctions under mechanical stress. Theoretical predictions were compared and validated against the experimental results. The integration of experimental and theoretical approaches provides a comprehensive understanding of the ML behavior of Pr3+-doped NaNbO3/LiNbO3 heterojunctions. The insights gained from this research contribute to the development of novel ML materials and pave the way for their applications in next-generation sensing and energy conversion devices.