The Bright X-Ray Stimulated Luminescence of HfO_2 Nanocrystals Activated by Ti Ions

摘要

The recent trends in scintillator technologies stimulate research efforts toward the development of novel materials morphologies, such as nanoparticles, able to efficiently convert ionizing radiations into light. For example, scintillating nanoparticles attract great interest in medical oncological therapies. In this work, the structural and morphological properties of HfO2:Ti nanoparticles with Ti concentrations from 0.03 to 10 mol% and subjected to calcination up to 1000 degrees C are thoroughly characterized; moreover, X-ray photoelectron spectroscopy reveals the incorporation of Ti in both Ti (III) and Ti (IV) chemical states in as prepared samples, while the exclusive presence of Ti(IV) is unambiguously identified in calcined nanoparticles. The optical emission under X-ray excitation evidences an intense Ti (IV)-related luminescence at 2.5 eV in high temperature calcined samples with a few microseconds scintillation lifetime, and efficiency comparable to that of Bi4Ge3O12 reference scintillator. Finally, the competitive role of defects in charge carriers capture is demonstrated by the monotonic increase of the 2.5 eV band during prolonged X-ray irradiation, more evident for nanoparticles with titanium concentration below 1 mol%. HfO2:Ti may also find application in X-ray triggered oncological therapies by using the Ti (IV)-related bright radioluminescence to excite photosensitizer molecules for singlet oxygen generation.