Water Molecules in Zeolite Y Enhance the Photoluminescent Properties of Its Cesium Lead Bromide Quantum Dots, Na4Cs6PbBr48+

Zeolite Pb,Br,H,Cs,Na-Y was prepared by the reaction of Cs49Na22-Y with PbBr2 in a mixed organic solvent, and the structure of a single crystal of it was determined crystallographically. About 26% of its supercages hold a tetrahedral PbBr42- ion at their centers. Each is surrounded by six Cs+ ions, each of which bridges between the two Br- ions on each edge of the PbBr42- tetrahedron. Each of these four Br- ions also bonds to a Na+ ion near the center of a 6-ring. The result is a Na4Cs6PbBr48+ quantum dot (QD) of symmetry (4) over bar 3m (T-d). The supercage in this zeolite (Si/Al = 1.69) has an average charge of 8.9-, which nearly balances the 8+ charge of this QD. Water molecules in 12-rings bridge (Cs+-H-2 O-Cs+) between QDs in adjacent supercages to form domains of tetrahedrally arranged QDs. Both these QDs and these domains are seen directly by electron microscopy. These QDs, when excited by UV radiation, luminesce sharply at 528 nm (green, FWHM = 17.8 nm). Pb,Br,H,Cs,Na-Y and its luminescence are entirely stable in the atmosphere; the bridging water molecules enhance the luminescence and provide that stability. Structure refinement was done in the space group Fd (3) over barm (a = 24.889(4) angstrom) with the 886 unique reflections for which F-o > 3 sigma(F-o) to the final error index R-1 = 0.077. Its composition was confirmed by energy dispersive X-ray analysis.