Tailoring bandgap and trap distribution via Si or Ge substitution for Sn to improve mechanoluminescence in Sr3Sn2O7:Sm3+ layered perovskite oxide

Two new compounds, Sr3(Sn2-xSix)O7:Sm3+ and Sr3(Sn2-xGex)O7:Sm3+, were synthesized by a solid-state reaction method and their structure, optical bandgap, trap distribution and related phosphorescence and mechanoluminescence (ML) properties were investigated. The results showed that a solid solution with a layered perovskite structure was formed and the ML was increased by introducing Si or Ge. For typical compositions of Sr2.994Sm0.004(Sn1·9Si0.1)O7 and Sr2.994Sm0.004(Sn1.75Ge0.25)O7, the ML intensities were are about 1.40–1.47 and 2.45–2.60 times than that of Sr2.994Sm0.004Sn2O7, respectively, and the threshold of the compression load above which the linearity of the ML curves changed greatly. The absorption spectra, phosphorescence decay curves, and thermoluminescence showed that adjusting the optical bandgap and trap distribution may improve the ML properties. A moderate reduction of the bandgap increased the electron trapping during the UV pre-excitation, whereas broadening the energy gap hampered electron detrapping. Increasing the trap density increased the quantity of trapped electrons or holes. Our result implies that adjusting the optical bandgap and trap distribution may be a new route for developing high-intensity mechanoluminescent materials.