Enhancing the mechanoluminescence of traditional ZnS:Mn phosphors via Li+ Co-doping

Mechanoluminescent materials that could convert mechanical energy into light energy have attracted increasing attention in recent years for their wide potential applications in stress sensing and imaging, structural damage monitoring, wearable illuminating devices, self-powered display, mechanical energy collection and conversion. However, their relatively low mechanoluminescence intensity greatly hinders the practical application. Here, we present a simple and effective strategy to enhance the mechanoluminescence performance of ZnS:Mn phosphor by Li ion co-doping. ZnS:Mn,Li phosphors of the hexagonal wurtzite structure have been prepared via high temperature solid phase sintering. The PL and ML intensity have been enhanced by 338% and 610% for samples obtained when 4 and 5 at. % Li is introduced in the precursor materials, respectively, in comparison with those without Li dopant. The photoluminescence lifetime of ZnS:Mn,Li decreases gradually, indicating the enhanced non-radiative energy transfer as the Li concentration increases. The electron paramagnetic resonance spectroscopy is carried out to investigate the changing tendency of the sulfur vacancy of samples with various Li-doping concentration. The mechanism for mechanoluminescence enhancement is supposed to be correlated with the increased sulfur vacancies by Li co-doping, which may facilitates the non-radiative energy transfer and thereby improve the luminescence properties of the samples. These findings provide a feasible strategy to enhance the mechanoluminescence performance of traditional ZnS derived phosphors, and may contribute to developing novel mechanoluminescence materials for practical applications.