Preparation of Metallic Tungsten Oxide Nanoparticles for Visible Upconversion Emission Enhancement

It is well known that localized surface plasmon resonance (LSPR) enhances fluorescence from adjacent luminescent materials. This LSPR effect is also effective for infrared (IR) to visible light upconversion emission. Gold and silver nanoparticles are typical nanoparticles with LSPR, but they are not the suitable materials for visible upconversion emission because they absorb visible light. Transition metal oxides are usually transparent in the visible light region but they are insulators. However, they can form metallic phases due to the presence of oxygen defects. In fact, tungsten oxide WO_3-x is known to form a metallic phase at x=0.3. Therefore, metallic tungsten oxide nanoparticles are one of the candidates for materials to gain upconversion luminescence in the visible range.<br/><br/>In this study, we have prepared metal tungsten oxide nanoparticles with LSPR in the infrared region by sputtering method. Atomic force microscopy revealed that the diameter of these nanoparticles was approximately 50 nm. Hall measurements showed that the nanoparticles were metallic with a carrier density of 5.9×10²²cm^-3 at room temperature. X-ray diffraction measurements showed that the nanoparticles were crystalline. The nanoparticles had a peak in optical absorption by LSPR at around 960 nm. These results indicate that metallic tungsten oxide nanoparticles have the potential to enhance the upconversion emission from IR to visible light in Er³⁺ doped glass ceramics. Details of upconversion enhancement using LSPR of metal tungsten oxide nanoparticles will be presented and discussed at the meeting.