Investigation of HfO2 nanoparticles intrinsic luminescence

Luminescent materials have found a wide variety of applications as phosphors for fluorescent lighting, display devices, X-ray monitoring and imaging, scintillators, and biomedical imaging. Indeed, the research in nanosciencehasbeen especially dedicated to the development of synthesis routes with the ability to synthetizenew material structures for industrial applications [1]. Fervent research in nanostructured materials has resulted in the development of novel synthetic methods to prepare pure and doped luminescent materials, and strategies to control the incorporation of dopant ions in nanoparticles. Hafnium oxide (HfO2) is considered as an attractive material because of its excellent physical and chemical properties, such as its high dielectric constant and insulating characteristics, which allow its application as a dielectric material with relatively high refractive index and wide band gap, as well in the field of optical coatings and next generation metal-oxide semiconductor devices. Moreover in recent investigations, nanometric hafnia when properly doped by rare earths (RE) ions has been also considered for optical applications [2]. Given the importance of HfO2 as host material for RE, its intrinsic optical response is also worth of investigation. In this work, we propose the study of the luminescent properties of undoped HfO2nanoparticles (NPs), achieved through a non-aqueous sol-gel process. The optical properties were studied by photo- and radio-luminescence considering the effect ofthe size and of the crystal phase. A broad composite emission was observed in the visible range, potentially correlated to intrinsic surface defects. A spectral analysis was performed, and the luminescence efficiency was compared to that of standard luminescent materials. Our studies reveal that HfO2 nanopowders may represent an interesting system in both phosphor technology and scintillation applications.