Nanocrystalline monoclinic HfO 2 films with an average crystal size of 4.2–14.802nm were sputter deposited under controlled temperatures and their structural characteristics and optical and photoluminescence properties have been evaluated. Structural investigations indicate that monoclinic HfO 2 films grown at higher temperatures above 40002°C are highly oriented along the (6102111) direction. The lattice expansion increases with diminishing HfO 2 crystalline size below 6.802nm while maximum lattice expansion occurs with highly oriented monoclinic HfO 2 of crystalline size about 14.802nm. The analysis of atomic force microscopy shows that the film growth at 60002°C can be attributed to the surface-diffusion-dominated growth. The intensity of the shoulderlike band that initiates at ~025.702eV and saturates at 5.9402eV shows continued increase with increasing crystalline size, which is intrinsic to nanocrystalline monoclinic HfO 2 films. Optical band gap varies in the range 5.4002±020.03–5.6002±020.0302eV and is slightly decreased with the increase in crystalline size. The luminescence band at 4.002eV of HfO 2 films grown at room temperature can be ascribed to the vibronic transition of excited OH radical while the emission at 3.2–3.302eV for the films grown at all temperatures was attributed to the radiative recombination at impurity and/or defect centers.