Bright green emitters with adjustable photoluminescence (PL) maxima in the range of 530-535 nm and full-width at half-maxima (fwhm) of <25 nm are particularly desirable for applications in television displays and related technologies. Toward this goal, we have developed a facile synthesis of highly monodisperse, cubic-shaped formamidinium lead bromide nanocrystals (FAPbBr(3) NCs) with perovskite crystal structure, tunable PL in the range of 470-540 rim by adjusting the nanocrystal-size (5-12 nm), high quantum yield (QY) of up to 85% and PL fwhm of <22 nm. High QYs are also retained in films of FAPbBr(3) NCs. In addition, these films exhibit low thresholds of 14 +/- 2 mu J cm(-2) for amplified spontaneous emission.