Structural, optical and diluted magnetic semiconducting properties of pristine ZnO, Fe-doped (Zn_0.98Fe_0.02O), Ga-doped (Zn_0.98Ga_0.02O) and Ni-doped (Zn_0.98Ni_0.02O) ZnO thin films deposited by pulsed laser deposition technique have been studied. X-ray diffraction (XRD) studies reveal the nanocrystalline nature in single wurtzite phase of all the films. Optical bandgap of the films found to depend upon the transition/post-transition metal doping and has a maximum value (∼3.65 eV) for Zn_0.98Ga_0.02O film and lowest value (∼3.23 eV) for Zn_0.98Ni_0.02O film. SQUID-vibrating sample magnetometer studies confirm the ferromagnetic nature of all the films with well defined field dependent magnetization (M−H) curves and temperature dependent zero field cooled (ZFC) and field cooled (FC) curves. The origin of ferromagnetism in the present films has been analyzed under bound magnetic polarons (BMPs) and grain boundary specific area models. The present films are found to follow the grain boundary specific area model for the origin of ferromagnetism.