Quantum Dots of [Na₄Cs₆PbBr₄]⁸⁺, Water Stable in Zeolite X, Luminesce Sharply in the Green

Nanocrystals (NCs) of CsPbX₃, X = Cl, Br, or I, have excellent photoluminescent properties: high quantum yield, tunable emission wavelengths (410−700 nm), and narrow emission band widths. CsPbBr₃ NCs show high promise as a green-emitting material for use in wide color gamut displays. CsPbBr₃ NCs have, however, not been commercialized because they are sensitive to moisture and heat. To avoid these problems, this work attempts to introduce CsPbBr₃ into five zeolites. The zeolite X product, Pb,Br,H,Cs,Na−X, shows superior stability toward moisture, maintaining its initial luminescence properties after being under water for more than a month. Its structure, determined using single-crystal X-ray crystallography, shows that quantum dots (QDs) of [Na₄Cs₆PbBr₄]⁸⁺ (not of CsPbBr₃) have formed. They are tetrahedral PbBr₄²⁻ ions (Pb−Br = 3.091(11) Å) surrounded by Na⁺ and Cs⁺ ions. Each fills the zeolite's supercage with its Pb²⁺ ion precisely at the center, a position of high symmetry. The peaks in the emission spectra of Pb,Br,H,Cs,Na−X and the CsPbBr₃ NCs are both at about 520 nm. The FWHM of Pb,Br,H,Cs,Na−X, however, is narrower than any previously reported for any of the CsPbBr₃ NCs, and for zeolite Y and the various mesoporous materials treated with CsPbBr₃.