Mechanoluminescence of samarium(III) sulfate crystals activated by ultrasound

The mechanoluminescence (ML) was detected, when Sm2(SO4)3·8H2O crystals were exposed to a titanium waveguide with a 22 kHz ultrasonic disperser. It was shown that ML of this salt is not recorded during grinding with a stirrer compared to that found previously for any other Ln3+ crystal hydrates (Ln = Ce, Pr, Gd, Eu, Tb, and Dy). This is mainly because of low quantum yield of Sm3+ photoluminescence (PL) compared to those of these ions. The ultrasound increases significantly the rate and intensity of a mechanical action on the crystals to provide a stable and bright glow sufficient to record an ML spectrum. The lines of molecular nitrogen are observed at 290–430 nm in the luminescence spectrum in air atmosphere. The luminescence of Sm3+ ion is also detected with maxima at 560, 595, 640, 700, and 781 nm that correspond to the 4G5/2 → 6Hj/2 transitions and coincide with quasilines in a PL spectrum of the samarium(III) sulfate crystals. The lines of N2 arise due to discharges in the gas phase between surfaces charged oppositely during the ultrasonic treatment of crystals. The ML of Sm3+ ion is probably due to the excitation of luminescence by electroluminescence of crystal phosphors, namely, due to the separation and recombination of charge carriers in the electric field of a crystalline layer arising during mechanical action.