Influence of 120 MeV Au Ion Irradiation on Phase Transition, Surface, and Optical Properties of Lead-Free (K,Na)NbO3 Films

High energy ion beam irradiation is an important tool to engineer the properties of multifunctional materials for diverse applications. The present study reports the impact of 120 MeV Au ion beam irradiation on structural and luminescence properties of (K,Na)NbO3 (KNN) films. The increase in ion fluence has resulted in crystalline-to-crystalline and crystalline-to-amorphous phase transitions at room temperature. The dense grain-like morphology of crystalline films gets transformed into clusters of nano-sized grains after irradiation, and the grain boundaries are diffused at higher fluence. X-ray photoelectron spectroscopy results indicate the evaporation of K-species from the surface after irradiation. The relative elemental ratio and film's thickness were estimated using Rutherford backscattering spectrometry, and subsequently, KNN/Si interface analysis was also carried out. The increase in optical band gap after irradiation is correlated to the suppression of extended band tails. An intense photoluminescence emission in the UV region is observed, and the intensity increases abruptly after the crystalline-to-amorphous phase transition, where the grain boundaries merge with nearby ones. The impact of high electronic energy loss in KNN enhanced the probability of radiative recombination. The obtained results demonstrate the possible use of KNN for optoelectronic applications.