A new class of battery-free, mechanically powered, piezoelectric Ca5Ga6O14:Tb3+ phosphors with self-recoverable luminescence

Abstract

Mechanoluminescent (ML) phosphors, which are capable of converting mechanical energy into photons, are of great interest in a wide range of fundamental applications. However, most of the discovered ML phosphors are limited to trap-controlled types, hindering them from operating in fields where dark working conditions are required since the recovery of the ML intensity needs light re-irradiation. Herein, a mechanically powered Ca₅Ga₆O₁₄:Tb³⁺ phosphor, featuring trap-independent, self-recoverable mechanoluminescence, and a low mechanical stimulus threshold, is reported. Systematic experimental and theoretical studies are performed to reveal the origin of the mechanoluminescence, demonstrating that the mechanoluminescence is dictated by piezoelectricity as a result of the non-centrosymmetric mm2 point group of the Ca₅Ga₆O₁₄ host. Density functional perturbation theory (DFPT) is used to study the piezoelectric properties, and due its polar structure, the host possesses giant piezoelectric coefficients with d_ij and e_ij as high as 4.417 pm V⁻¹ (d₂₄) and 1.27 × 10⁻¹⁰ C m⁻² (e₃₁), respectively, which are comparable to or even higher than those of many frequently used piezoelectric materials. Owing to these admirable ML properties, the newly found Ca₅Ga₆O₁₄:Tb³⁺ phosphor has the potential for battery-free, energy-saving piezo-photonic applications.