Thermally induced reversible phase transition and photoluminescence switching behavior of (NH4)2MnBr4(H2O)2 crystals

Abstract

Organic–inorganic hybrid perovskite materials possess broad application prospects in photodetectors, light-emitting diodes (LEDs), and anti-counterfeiting due to their excellent optoelectronic properties; however, their development is still restricted by stability. In this paper, a new type of (NH₄)₂MnBr₄(H₂O)₂ perovskite single crystal was synthesized using a simple solvent evaporation method. The thermally induced loss of water molecules in the crystal results in a reversible phase transition, accompanied by a change in photoluminescence (PL) from non-emission to red emission (660 nm), and the red emission originates from the d–d transition of Mn²⁺ (⁴T₁–⁶A₁). Additionally, the structure and luminescence behavior of the sample remain stable after 30 dark–red–dark cycles. (NH₄)₂MnBr₄(H₂O)₂ demonstrates excellent environmental stability, as evidenced by the unchanged structure after 180 days and resistance to interference from various solvents. Notably, by exploiting the characteristics of the material and combining it with Cs₃Cu₂Br₅, we demonstrated a multi-dimensional information encryption anti-counterfeiting label based on temperature and time gradients. This material offers a new option for thermochromic materials in anti-counterfeiting applications.