The authors report on the microstructural characteristics of sputter-deposited thin film ZnGa2O4: Mn phosphors, with an emphasis on the role of energetic particle bombardment. The. thin film ZnGa2O4:Mn phosphors were deposited by radio frequency planar magnetron sputtering of a 2 mol % Mn-doped ZnGa2O4 target in an Ar-O-2 gas mixture at gas pressures ranging from 2 to 20 mTorr. The growth rate of the ZnGa2O4:Mn films was decreased from 40 to 23 angstrom/min as the gas pressure was raised due to both increased gas-phase scattering as well as reduced target self-bias voltage. Owing to the thermalization of impinging energetic particles and the randomization in their incidence directions when arriving at the substrate, the ZnGa2O4:Mn films produced at an elevated gas pressure exhibited a porous composite microstructure in which larger columns consisted of bundles of smaller columns separated by voided boundaries. Energetic particle bombardment of the growing film surface at a low gas pressure yielded a densely packed zone-T-type microstructure due to porosity annihilation by knock-on processes and bombardment-enhanced adatom mobility. Atomic force microscopy and grazing incidence x-ray reflectivity data revealed that as the gas pressure was decreased from 20 to 2 mTorr, the rms surface roughness of the deposited ZnGa2O4: Mn films was reduced from 4.95 to 1.23 nm and the film density increased from 5.314 to 5.681 g/cm(3), consistent with the postulated effects of energetic particle bombardment upon film microstructure. (c) 2006 American Vacuum Society.