Visible to Near-Infrared Luminescence and Reversible Photochromism in Mn2+/Nd3+ Co-Doped Double Perovskite for Versatile Applications

Multifunctional optical materials with temperature sensing and anti-counterfeiting properties play an essential role in the commercial applications. Herein, Mn²⁺/Nd³⁺ co-doped Cs₂AgInCl₆ (CAIC) lead-free double perovskites (DPs) is synthesized through a hydrothermal method, which exhibits visible to near-infrared (NIR) luminescence and reversible photochromic properties from yellowish to dark purple. The mechanism investigations on the photoluminescence and photochromic phenomena reveal that the incorporation of Mn²⁺ ions not only acts as an intermediary in the energy transfer process from the host exciton to Nd³⁺ ions, but also plays a pivotal role in the reversible photochromic response. The temperature-dependent luminescence, attributed to the contrasting thermal responses of Mn²⁺ and Nd³⁺ ions, enables precise temperature sensing via the fluorescence intensity ratio method. In addition, the integration of visible red emission, NIR luminescence, and photochromic properties in a single CAIC: Mn²⁺/Nd³⁺ DPs, offers a multilevel anti-counterfeiting strategy. The multifunctional CAIC: Mn²⁺/Nd³⁺ DPs would open up new avenues for advanced optical applications, particularly in the realms of temperature sensing and security anti-counterfeiting.