Intense and Stable Blue Light Emission from CsPbBr3/Cs4PbBr6 Heterostructures Embedded in Transparent Nanoporous Films

Lead halide perovskite nanocrystals are attractive for light emitting devices both as electroluminescent and color converting materials, since they combine intense and narrow emissions with good charge injection and transport properties. However, while most perovskite nanocrystals shine at green and red wavelengths, the observation of intense and stable blue emission still remains a challenging target. In this work, we report a method to attain intense and enduring blue emission (470-480 nm), with a photoluminescence quantum yield (PLQY) of 40%, originated from very small CsPbBr3 nanocrystals (diameter<3nm) formed by controllably exposing Cs4PbBr6 to humidity. This process is mediated by the void network of a mesoporous transparent scaffold in which the zero-dimensional Cs4PbBr6 lattice is embedded, which allows the fine control over water adsorption and condensation that determines the optimization of the synthetic procedure and, eventually, the nanocrystal size. Our approach provides a means to attain highly efficient transparent and stable blue light emitting films that complete the palette offered by perovskite nanocrystals for lighting and display applications.