Quantum Dots of [Na 4 Cs 6 PbBr 4 ] 8+ , Water Stable in Zeolite X, Luminesce Sharply in the Green

Nanocrystals (NCs) of CsPbX 3 , X = Cl, Br, or I, have excellent photoluminescent properties: high quantum yield, tunable emission wavelengths (410−700 nm), and narrow emission band widths. CsPbBr 3 NCs show high promise as a green‐emitting material for use in wide color gamut displays. CsPbBr 3 NCs have, however, not been commercialized because they are sensitive to moisture and heat. To avoid these problems, this work attempts to introduce CsPbBr 3 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 [Na 4 Cs 6 PbBr 4 ] 8+ (not of CsPbBr 3 ) have formed. They are tetrahedral PbBr 4 2− ions (Pb−Br = 3.091(11) Å) surrounded by Na + and Cs + ions. Each fills the zeolite's supercage with its Pb 2+ 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 CsPbBr 3 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 CsPbBr 3 NCs, and for zeolite Y and the various mesoporous materials treated with CsPbBr 3 .