Dual‐Mode Thermal Responses in Red and Near‐Infrared Emission Channels via Manipulating Cross Relaxations

Abstract Lead‐free double perovskites with multi‐mode emission characters are highly desired for optoelectronic devices. Herein, dual‐mode thermal responses with low thermal quenching in the red emission channel and high thermal quenching in the near‐infrared (NIR) channel are achieved in a holmium‐based double perovskite (Cs₂NaHoCl₆). The temperature‐dependent emission is modulated by manipulating three cross relaxations of CR1 (⁵F₄, ⁵I₇) → (⁵F₅, ⁵I₆), CR2 (⁵S₂, ⁵I₈) → (⁵F₅, ⁵I₇), and CR3 (⁵F₅, ⁵F₅) → (⁵I₇, ⁵G₄) through adjusting the concentration of Ho³⁺. The difference in thermal response between the red and NIR emissions becomes more pronounced with a higher concentration of Ho³⁺ up to 100%, while the two emissions show almost the same thermal quenching behavior when the Ho³⁺ concentration is below 20%. To demonstrate their applications, a thermal‐responsive dual‐mode information encryption system and a NIR emitting LED with night vision capacity are fabricated using the prepared samples. This study provides a new approach for thermal quenching regulation in rare‐earth‐based lead‐free perovskites and illustrates their potential in lighting, anti‐counterfeiting, and sensing applications.