White-Light Emission from the Structural Distortion Induced by Control of Halide Composition of Two-Dimensional...

Two-dimensional (2D) perovskites, which have a 2D orientation of the inorganic framework that determines largely the electronic characteristics and an organic cation in the interlayer that leads to a quantum well structure, have attracted a great deal of attention due to their superior stable optoelectronic properties. Especially, some of the greatest interest in 2D perovskites is their application in broad-band white-light emission for solid state lighting. We prepared (BZA)₂PbBr_{4- x}Cl _x (BZA= benzylammonium and x = 0, 1.5, 2, 3, 3.5, 4) to tune the white-light emission. In the (BZA)₂PbBr₄ perovskite structure, the bond lengths of Pb-Br for PbBr₆^2- exhibit the same lengths of 2.98 and 3.00 Å, respectively. However, in PbCl₆ octahedra the bridging Pb-Cl distances were 2.83/2.88 Å and 2.85/2.88 Å, respectively. The 2D perovskite (BZA)₂PbCl₄ exhibits a turquoise light emission due to its highly distorted structure, whereas (BZA)₂PbBr₄ emits a narrow blue emission. We controlled the white emission by mixing the two compounds in proportion and changed the color from blue to white using the intermediate compound (BZA)₂PbBr_{4- x}Cl _x ( x = 1.5, 2, 3, 3.5). The intermediate compound (BZA)₂PbBr_{4- x}Cl _x ( x = 1.5, 2, 3, 3.5) shifted in the white space of Commission Internationale de l'Éclairage coordinates, which were (0.324, 0.383), (0.312. 0.369), (0.319, 0.374), and (0.338, 0.396), respectively. The correlated color temperature of all compounds was observed above 5000 K, which suggests that these perovskites could be utilized as "cold" white-light-emitting materials.