Ultra-long-delay sustainable and short-term-friction stable mechanoluminescence in Mn2+-activated NaCa2GeO4F with centrosymmetric structure

Energy-storage mechanoluminescent (ML) materials have shown promising prospects in stress sensing, lighting and displays due to the outstanding structural integrity and luminescent reproducibility. However, such ML materials universally encounter limitations in achieving long-delay sustainability, cyclic-stimulation stability and centrosymmetric-lattice availability. Herein, we report a new ML material NaCa2GeO4F:Mn2+ with centrosymmetric structure, whose ML properties show ultra-long-delay sustainability (up to a delay of 144 h), short-term-friction stability and high image contrast. The experimental and theoretical investigations indicate that these unique ML characteristics arise from the formation of deep traps. These deep traps can stably store a certain proportion of electrons at ambient temperature for a long time, and provide electronic supplement to shallow traps released under mechanical friction. The excitation mechanism of captured electrons under mechanical stimuli is attributed to the local triboelectric field caused by triboelectricfication. We also demonstrate the availability of the developed ML material in mechanically triggered display and time-resolved security encryption. Our results may provide new insights for developing high-performance energy-storage ML materials and promoting practical applications of such materials.