Up-Conversion Emissions from HfO₂: Er³⁺, Yb³⁺ Nanoparticles Synthesized by the Hydrothermal Method

Area of Science:

• Materials Science
• Nanotechnology
• Luminescence

Background:

• Hafnium oxide (HfO2) is a promising host lattice for up-conversion materials.
• Doping with rare-earth ions like Erbium (Er3+) and Ytterbium (Yb3+) enables up-conversion luminescence.
• Alkaline cations can potentially modify the optical properties of doped nanoparticles.

Purpose of the Study:

• To synthesize and characterize HfO2 nanoparticles doped with Er3+ and Yb3+ ions.
• To investigate the effect of codoping with Li+ and Na+ on up-conversion luminescence.
• To optimize the doping concentrations for maximum emission intensity.

Main Methods:

• Hydrothermal synthesis of HfO2 nanoparticles (approx. 80 nm) followed by high-temperature annealing.
• Characterization using X-ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS).
• Photoluminescence (PL) and Cathodoluminescence (CL) spectroscopy to study up-conversion emission under infrared and electron beam excitation.

Main Results:

• Single doping with Er3+ showed inefficient emission, with optimal performance at 7 at % Er3+.
• Co-doping with Er3+/Yb3+ significantly improved up-conversion efficiency, with optimal intensity at 3 at % Er3+ and 7 at % Yb3+.
• Codoping with Li+ and Na+ cations further enhanced the up-conversion luminescence intensity, with observed emission bands in the green (~523, 544 nm) and red (~652, 673 nm) spectral regions.

Conclusions:

• HfO2 nanoparticles doped with Er3+/Yb3+ and codoped with Li+/Na+ are efficient up-conversion materials.
• Optimization of doping concentrations and the inclusion of alkaline cations are crucial for enhancing luminescence.
• These materials show potential for applications requiring efficient light conversion under infrared or electron beam excitation.