Near Infrared to Visible Upconversion Polarization Imaging Enabled by Cs₂NaScCl₆:Er³⁺ Composite Film

Current near-infrared (NIR) polarization imaging relys on expensive, cryogenically cooled infrared detectors with resolution, toxicity, and system complexity limitations. Herein, we propose a NIR polarization imaging system based on Cs₂NaScCl₆:Er³⁺ upconversion emissive film and a commercial visible camera. Cs₂NaScCl₆, a lead-free double perovskite, was selected as the host matrix for its non-toxicity, wide bandgap, and ability to accommodate high-concentration Er³⁺ doping. We optimized the Er³⁺ doping concentration to 12%, achieving a high photoluminescence quantum yield (PLQY) of 5.98% under 980 nm excitation, with emission peaks located at 551 nm. The as-fabricated powder was 600-mesh sieved for refinement. Subsequently, the post-processing Cs₂NaScCl₆:Er³⁺ powders were dissolved in polydimethylsiloxane (PDMS) to fabricate uniform, flexible, and environmentally stable composite films, which maintain retained excellent upconversion emission even after 30-day storage. The NIR polarization imaging system combines the upconversion film with the dual-orthogonal linear polarization detection scheme, enabling the extraction of the full Stokes vector, degree of linear polarization (DOLP), and angle of polarization (AOP). This system outperforms traditional NIR cameras in background suppression and material distinction, and operates without cryogenic cooling. This modular, low-cost approach expands the application of perovskite optoelectronics and provides a practical path for high-resolution NIR polarization imaging across multiple fields.