van der Waals layered materials have garnered enormous attention for their unique electronic and optical properties. Among them, γ-indium selenide (γ-InSe) exhibits a thickness-dependent crossover from a direct to an indirect band gap. Here, we report strain-induced sub-band gap infrared photoluminescence (PL) in γ-InSe by applying local strain via SiO2 nanopillars. The broad sub-band gap emission is confined to the strained sites and vanishes above 200 K. Density functional theory calculations, combined with laser power-dependent PL and time-resolved PL measurements, suggest the defect origin of the emission caused by selenium vacancies. These findings elucidate strain-defect interactions in layered γ-InSe and indicate a pathway to defect-based optoelectronics and quantum-emitter devices.
Keywords: DFT calculation; indium selenide; photoluminescence; strain effect; van der Waals materials.