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 Cs₂MIMIIICl₆ (MI = Ag⁺, Na⁺; MIII = 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 MIII 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 MIII 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⁺ f-f 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.