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Perovskite nanocrystals have shown tremendous potential in the field of optoelectronics, finding numerous applications. Rare-earth elements serve as excellent alternatives to lead in perovskite nanocrystals owing to their abundant 4f energy level and distinct electronic arrangement. By partially or completely replacing lead, these elements not only reduce the environmental impact, but also introduce a range of unique effects and applications. More details are discussed in the review article by Zhang et al. on page 1032—1056.