Tunable excitation in nitrided amorphous TiO2:Eu

Abstract

Developing luminescent materials with broadband optical response is of fundamental importance for various applications, including photovoltaics, biological imaging and photonics. However, the task of engineering the optical excitation with tunable feature in doped luminescent materials has been met with limited success, owing to the limited space for modifying dopant-host interactions. Here, we present an effective strategy for control of the light-harvesting process, based on the collaborative nitriding and annealing in amorphous TiO2:Eu. The structural characterizations, including X-ray Diffraction (XRD) and transmission electron microscopy (TEM), indicate that the phase of nitrided TiO2:Eu can be well kept in amorphous form below 500 °C. X-ray photoelectron spectroscopy (XPS) confirms that the N content can be well controlled by changing the annealing temperature. The samples present notable absorption in the broad waveband region from 400 to 1000 nm, which is associated with the band tail states induced by nitriding. The doping engineering allows us to achieve broadband and tunable excitation covering the whole ultraviolet waveband from 250 to 400 nm. We also demonstrate the construction of composite layer which exhibits intense visible luminescence under ultraviolet and X-ray irradiation. Our results outline a fundamental principle to design light-harvesting materials with extended optical response, providing a major step toward in expanding the scope of lanthanide-doped phosphor.