Intense red photoluminescence and mechanoluminescence from Mn²⁺-activated SrZnSO with a layered structure

A series of novel red emitting Mn²⁺-activated SrZnSO phosphors were successfully synthesized by solid-state reaction at high temperature. The photoluminescence (PL) and mechanoluminescence (ML) properties of these Mn²⁺-activated SrZnSO phosphors with different Mn²⁺ concentrations were investigated. With increasing the concentration of Mn²⁺ from x = 0 to 0.04, the unit cell volume increased from 153.82 to 154.19 ų while the optical band gap decreased from 3.74 to 3.43 eV. The site occupation of Mn²⁺ in the host lattice was demonstrated by Rietveld refinement, the electron paramagnetic resonance (EPR) spectrum, and the spectroscopic properties. A broad band emission peak at 603 nm of SrZn_1-xMn_xSO (0.001 ≤ x ≤ 0.04) with an excitation wavelength of 318 nm was attributed to electronic transitions of Mn²⁺ from the ⁴T₁(⁴G) level to the ⁶A₁(⁶S) level. The lifetime of SrZn_1-xMn_xSO (0.001 ≤ x ≤ 0.04) decreased monotonously from 2.97 to 0.82 ms with increasing Mn²⁺ concentration. In particular, intense emission of red light from SrZn_1-xMn_xSO (0.001 ≤ x ≤ 0.04) under compressive load could be observed even with the naked eye, indicating that SrZn_1-xMn_xSO could be used for stress sensors or stress imaging. There was a linear correlation between the ML intensity and external load in SrZn_1-xMn_xSO, and the ML intensity could be recovered under UV light irradiation. Considering its advantages of non-destruction, reproducibility, and high ML intensity, SrZn_1-xMn_xSO might be useful for non-destructive detection of stress.