Coexistence of self-reduction from Mn4+ to Mn2+ and elastico-mechanoluminescence in diphase KZn(PO3)3:Mn2+

Abstract

Mechanoluminescence (ML) materials have attracted much attention for potential applications in many real-time nondestructive detection and anti-counterfeiting fields; however, obtaining an orange-red emission color remains a challenge. As one of the red activators, Mn²⁺ has excellent optical performance. Herein, elastico-ML materials with self-reduction of Mn⁴⁺ to Mn²⁺ were developed by selecting piezoelectric hosts with flexible frames and a large defect capacity. The divalent state of Mn was demonstrated by X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), photoluminescence (PL) spectroscopy, and X-ray absorption fine structure (XAFS) spectroscopy. A tunable luminescence from red to orange was realized and a bright red light was observed under weak mechanical stimulation. The optical and structural characteristics revealed that a unit cell with a low stiffness and large space to accommodate cation defects is a fundamental factor for the ML phenomena. This study not only offers a unique insight for understanding the self-reduction and ML phenomena of Mn²⁺-doped functional materials, but also expands the applications of advanced optical functional materials in stress sensors and optical information storage.