Mechanoluminescence Affected by Trap Types and Excitation State Positions in Mg3Ca3(PO4)4:Eu2+/Mn2+/Ce3+ for Multimode Anticounterfeiting.

ABSTRACT

Mechanoluminescence (ML) materials with tunable emissions can serve in many practical applications; however, their underlying mechanism still needs further clarification. Herein, we developed Eu2+-/Mn2+-/Ce3+-activated Mg3Ca3(PO4)4 (MCP) phosphors and studied their luminescence properties by device fabrication. The intense blue ML is obtained by fabricating MCPEu2+ into the polydimethylsiloxane elastomer matrix. The red ML of relatively weak intensity is received in Mn2+ activator, but the ML for the Ce3+ dopant is nearly quenched in the same host. The possible reason is proposed from the analysis of the relative positions between the excitation state and conduction band, together with the trap types. The appropriate location of the excited energy levels in the band gap allows for a larger probability of efficient ML when shallow traps near the excitation states are created synchronously as an effective energy transfer (ET) channel. The concentration-dependent ML for the MCPEu2+,Mn2+-based devices indicates that the emitting light color can be tailored, where several ET processes among oxygen vacancies, Eu2+, Ce3+, and Mn2+, occur. The luminescence manipulation with dopants and excitation sources demonstrates the potential applications in visualized multimode anticounterfeiting. These findings open up many possibilities for constructing new ML materials by introducing appropriate traps into the band structures.