All-inorganic halide perovskites(IHP),CsPbX3(X = Cl,Br,I)exhibiting efficient optical emissions within the spectral range of 410 to 730 nm are potential candidates for many optoelectronic devices.Anion alloying of these IHPs is expected to achieve tunable emission wavelength covering the entire visible spectrum.Here,we developed a two-step chemical vapor deposition(CVD)process for growing quaternary IHP CsPbX3(X = Cl/Br and Br/I)alloys.By exploiting the fast diffusion of halide anions in IHPs,the alloy composition can be precisely controlled by the growth time of the respective layers once the growth of the individual ternary IHP is optimized.Hence complexities in the multi-parameter optimization in the conventional CVD growth of quaternary alloys can be mitigated.Using this process,we synthesized single crystalline,homogeneous and thermally stable CsPbCl3(1-x)Br3x and CsPbBr3(1-x)l3x perovskites alloy microplates and demonstrated continuously tunable emission covering the spectrum from 428 to 715 nm by varying the halide compositions in the alloys.These alloy microplates also exhibit room temperature amplified spontaneous emissions(ASE)along with strong photonic discharges from the microplate's edges and hence are potentially useful as a gain medium as well as optical cavities for emissions with wavelengths covering the visible spectrum.