Controllable Synthesis of Gradient α/β-ZnS:Cu for Revealing the Mechanoluminescent Mechanisms

ZnS:Cu, with interband direct transition, exhibits complex and tunable emission spectra due to the additional energy levels introduced by Cu doping, making it ideal for mechanoluminescent devices. However, the coexistence of α- and β-ZnS:Cu phases and diverse Cu ion doping complicates the coupling of various luminescent processes and understanding its mechanoluminescent mechanism. Here, the gradient α/β-ZnS:Cu with pure-phase and single-structure has been synthesized through an oxygen-assisted variable-temperature rapid cooling sintering method with low Cu concentration. Oxygen introduction promoted the formation of sulfur vacancies, enabling precise regulation of Cu doping amount and site. By fine-tuning the sintering process and Cu concentration, the composition of α/β-ZnS:Cu was adjusted precisely while suppressing impurities. Using this tunable-gradient α/β-ZnS:Cu, the complex luminescence processes were decoupled, confirming that the piezoelectricity of ZnS:Cu directly stimulates mechanoluminescence generation. This understanding proves valuable in refining the mechanoluminescence mechanism and enhancing the design of mechanoluminescent materials.