Lead-Free Rare-Earth Based Halide Double Perovskites: From Fundamentals, Progress to Perspectives

Abstract

Lead-free halide double perovskites are rapidly gaining prominence as a nontoxic, highly stable, and versatile alternative to traditional lead-based perovskites, notable for their superior optoelectronic properties. Among these, rare-earth-based halide double perovskites (RHDPs) notably stand out. Comprising fifteen lanthanide elements with distinctive electron configurations of [Xe] 4f ⁿ⁻¹ 5d⁰⁻¹ 6s² (n = 1–15), alongside the group-IIIB elements Yttrium (Y) and Scandium (Sc), rare-earth elements (RE) exhibit great potential. These 17 RE ions (Sc³⁺, Y³⁺, and La³⁺–Lu³⁺) offer a vast landscape for crafting numerous RHDPs, poised to exhibit properties that surpass and diversify beyond current double perovskite standards. Key to their functionality are unique luminescence properties driven by self-trapped exciton (STE) recombination, and 4f→4f and 5d→4f transitions, enabling applications in visible and infrared light emission through downshifting and up-conversion. This review thoroughly articulates the foundational properties of RHDPs, including their structural-property relationships, synthesis methods, optical characteristics, and durability. It highlights recent advancements in their applications across a range of fields such as visible and near-infrared light emitting diodes (Vis&NIR LEDs), sensors, and anti-counterfeiting technologies. Additionally, the review discusses the prevailing challenges associated with RHDP materials and their applications, offering insights and future directions.