Here, (K,Na)NbO3 (KNN) films were synthesized using RF sputtering under Ar:O2 (3:1) environment, and eventually annealed by rapid thermal annealing (RTA), and conventional furnace annealing (CFA), at different temperatures. Crystalline films are observed with the evolution of well-shaped regular features of KNN perovskite after annealing, but the growth scenario is different in RTA and CFA. XPS results reveal the formation of an additional hump of Nb sub-oxides upon annealing via both processes. The transmittance of RTA films is higher than CFA ones where RTA@800 °C sample exhibits maximum transmittance with a sharp absorption onset. The band gap is reduced with annealing temperature and it gets decreased to a minimum of 3.19 eV for CFA@800 °C films. The samples exhibit an intense PL emission in the ultraviolet region, and the intensity of RTA films is much higher than CFA. A high decay lifetime of RTA films indicates the suppression of non-radiative decay channels.