Aqueous Solution Growth of Millimeter-Sized Nongreen-Luminescent Wide Bandgap Cs4PbBr6 Bulk Crystal

Millimeter-sized Cs4PbBr6 bulk single crystal that has no green luminescence was successfully grown from concentrated CsBr aqueous solution for the first time. Absorption spectrum indicates an optical absorption starting from 3.6 eV and a localized absorption in the range of 3.8-4.2 eV. Photoluminescence spectrum clearly shows that the crystal has no green emission. Along with the calculated electronic band structure, it is concluded that Cs4PbBr6 has a wide bandgap of 3.6 eV. Through vacuum annealing treatment, the green luminescence of the original nongreen-luminescent Cs4PbBr6 crystal was successfully activated, which is possibly due to the formation of CsPbBr3. This work gives the method to obtain millimeter-sized Cs4PbBr6 crystals from aqueous solution and suggests a route to activate its green luminescence. The results are significant for the deep understanding of the intrinsic properties and exploring the potential applications of wide bandgap Cs4PbBr6.