Sb3+ Doping-Induced Coordination Competition and Host-Guest Reversal in In-Based Metal Halides.

Sb3+-doped In-based metal halides represent a class of highly efficient luminescent materials; however, systematic studies on the effects of Sb3+ doping on the coordination-structure evolution and photophysical-property changes of In-based metal halides remain limited. Herein, we report an indium halide, (C21H22P)2InCl5. Its unique trigonal-bipyramidal configuration enables the [InCl5]2- unit to exhibit light-orange emission at 600 nm, with a photoluminescence quantum yield of 28.43%. Owing to the well-coordinated coupling between the blue emission of C21H22P+ and the light-orange emission of [InCl5]2-, (C21H22P)2InCl5 exhibits single-component tunable white-light emission. Upon further introduction of Sb3+, the (C21H22P)2In1-xSbxCl5 system undergoes a phase evolution from an orange-emitting phase to a yellow-emitting phase and finally to a non-emissive phase. Spectroscopic and structural analyses reveal that this emission-color transition originates from the gradual evolution of the coordination environment with increasing doping concentration. Specifically, the (C21H22P)2In1-xSbxCl5 system evolves from the coexistence of five-coordinate Sb/In units at low doping concentrations to six-coordinate Sb units coexisting with four-coordinate In units at intermediate doping concentrations and then to four-coordinate Sb/In units at high doping concentrations. The study shows that this evolution is the result of substitutional doping, coordination competition-driven structural reconstruction, and host-guest reversal caused by the exchange of host and guest roles. Finally, we demonstrate the application potential of these products in optical anti-counterfeiting based on their differentiated luminescence responses.