High-quality thin films were obtained directly by spin-coating glass substrates with suspensions of powdered cesium lead bromide (CsPbBr3) perovskite quantum dots (PQDs). The structural properties of the films were characterized via transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) analysis, and atomic force microscopy (AFM). The crystal structure of the CsPbBr3 PQDs was unique. The optical behavior of the CsPbBr3 PQDs, including absorption and emission, was then investigated to determine the absorption coefficient and band gap of the material. The CsPbBr3 PQDs were evaluated as active lasing media and irradiated with a pulsed laser under ambient conditions. The PQDs were laser-active when subjected to optical pumping for pulse durations of 70–80 ps at 15 Hz. Amplified spontaneous emission (ASE) by the CsPbBr3 PQD thin films was observed, and a narrow ASE band (∼5 nm) was generated at a low threshold energy of 22.25 μJ cm–2. The estimated ASE threshold carrier density (nth) was ∼7.06 × 1018 cm–3. Band-gap renormalization (BGR) was indicated by an ASE red shift and a BGR constant of ∼27.10 × 10–8 eV. A large optical absorption coefficient, photoluminescence (PL), and a substantial optical gain indicated that the CsPbBr3 PQD thin films could be embedded in a wide variety of cavity resonators to fabricate unique on-chip coherent light sources.