Blue-emitting CsI thin films

Cesium iodide (CsI) with a blue emission is a promising material for applications in optoelectronic and biomedical fields. However, the low-cost fabrication for CsI with a blue emission remains a challenge. In this work, a facile and green approach to prepare CsI thin films is demonstrated, in which deionized (DI) water makes it possible for non-luminescent CsI powder to form thin films with a blue emission of 415 nm at room temperature. The CsI crystals undergo a crystallization process during the evaporation of the aqueous solution, thus resulting in tensile lattice strain and reducing the bandgap of the CsI crystals. The density functional theory (DFT) calculation reveals that hydrostatic-tensile lattice strain leads to the decrease of the bandgap of CsI crystal. The as-prepared CsI thin films exhibit excellent optical stability that the photoluminescence intensity retains 85 % of initial one after one month in the air. This work is expected to move a step forward for the low-cost manufacturing of CsI films with low energy consumption for blue-emitting devices.