The perovskite CH3NH3PbBr3 films were synthesized by mixing the solution of CH3NH3Br and PbBr2. The effect of modulating the molar ratios of organic to inorganic content on morphology and optical properties of CH3NH3PbBr3 was explored. The optical band gap of CH3NH3PbBr3 can be tuned from visible to infrared regions by changing the CH3NH3Br content. It was also found that the photoluminescence (PL) emission intensity decreases and the emission colors of these films change from bright green to dark in a darkroom, with decreasing molar ratio. The electronic states of C, N, Br, Pb in CH3NH3PbBr3 films were investigated to clarify the tunability of the optical band gap and PL intensity. (C) 2015 Elsevier B.V. All rights reserved.