HfO₂ thin films are extensively applied in optical coatings and microelectronic devices. However, film defects, which are vital to the performance of the thin films, are still under intense investigation. In this work, the absorption, photoluminescence, and crystallization characteristics of HfO₂ films prepared by electron-beam evaporation and ion-assisted deposition are investigated in detail. Experimental results showed that high-temperature thermal annealing in air resulted in a reduced absorption coefficient, an increased bandgap width, and an increased degree of crystallization. After thermal annealing, an absorption shoulder near 5.8 eV was caused by excitons in the films, which were independent of oxygen vacancy defects and crystallization. Under 6.4 eV (193 nm) laser excitation, the photoluminescence spectrum showed five emission peaks for HfO₂ films both with and without thermal annealing. The emission peak near 4.4 eV was generated by the self-trapped exciton, and the peak near 4.0 eV was related to the OH group in the film. The oxygen vacancy defect-induced absorption of HfO₂ films in a broad spectral range significantly increased when HfO₂ film was re-annealed in Ar gas after first being annealed in air, while the photoluminescence spectrum showed no significant change, indicating that the emission peaks at 2.3, 2.8, and 3.4 eV were not related to oxygen vacancy defects.

The optical absorption mechanism and the preparation technology for achieving low absorption of HfO₂ thin films at 1064 nm were systematically investigated. Through molecular dynamics simulations and electron density of states calculations, it was determined that oxygen vacancies within the thin films significantly contributed to the absorption of 1064 nm light. HfO₂ thin film samples were synthesized using various deposition parameters, followed by comprehensive measurement and analysis of their crystal phase, fluorescence, and microstructure. Theoretical calculations and experimental results indicated that the crystallization of amorphous films increased the presence of oxygen vacancy defects, consequently enhancing film absorption. Notably, following heat treatment at 400 °C, one sample retained a predominantly amorphous structure while exhibiting minimal absorption, suggesting improved optical stability for inertial confinement fusion and industrial laser processing applications.