High-Entropy Double Perovskites with Tailored Multichannel Luminescence

Entropy engineering has emerged as a versatile strategy for designing metastable materials with synergistic properties and functionalities. Here, we present a facile solution method that yields a new series of high-entropy metal-halide double perovskites (HE-DPs). Single crystals of HE-DPs with a general formula of Cs₂M^IM^IIICl₆ (M^I = Ag⁺, Na⁺; M^III = In³⁺, Sb³⁺, Ho³⁺, Er³⁺, Bi³⁺, Yb³⁺, Dy³⁺, or Tb³⁺) are obtained under mild conditions. Structural and elemental analyses demonstrate the formation of high-entropy single-phase single crystals with five elements occupying the trivalent M^III site. The incorporation of multiple trivalent metal ions in a high-entropy manner appears to drastically improve the ambient stability of double perovskites up to more than three months. The optical bandgap is found to decrease upon alloying at the M^III site. Additionally, the random distribution of lanthanide ions within the crystal structure results in synergic electronic interactions between the lanthanide host and lanthanide-lanthanide ions. The interaction between lanthanides and host induces both broadband emissions and sharp Ln³⁺ <i>f</i>-<i>f</i> transitions, while the lanthanide-lanthanide proximity leads to efficient NIR-to-visible photon upconversion. Our work underscores the high-entropy strategy for developing robust lanthanide perovskites featuring tailored, multichannel optical properties for advanced lighting, display, and sensing applications.