Solvothermal synthesis of lanthanide-doped CaF₂upconversion nanoparticles using liquid-solid-solution approach

Area of Science:

• Materials Science
• Nanotechnology
• Photonics

Background:

• Upconversion nanoparticles (UCNPs) are crucial for bioimaging, security printing, and optoelectronics due to their unique emission properties.
• Lanthanide-doped calcium fluoride (CaF2) nanoparticles offer tunable luminescence for various applications.

Purpose of the Study:

• To synthesize and characterize Ho3+/Yb3+, Er3+/Yb3+, Tm3+/Yb3+, and Er3+/Tm3+/Yb3+ co-doped CaF2 nanoparticles.
• To investigate the photoluminescence properties and energy transfer mechanisms within these UCNPs.
• To evaluate the potential of Er3+/Yb3+ co-doped CaF2 UCNPs for latent fingerprint detection and security applications.

Main Methods:

• Solvothermal synthesis method for creating doped CaF2 nanoparticles.
• Characterization using X-ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), High-Resolution Transmission Electron Microscopy (HR-TEM), Raman spectroscopy, and photoluminescence spectroscopy.
• CIE-1931 chromaticity analysis to determine color coordinates and purity.

Main Results:

• Synthesized UCNPs exhibited pure green, red, blue, yellow, and white emissions under 980 nm excitation.
• Color purity for red, green, blue, and yellow emissions exceeded 90%, indicating excellent chromatic performance.
• Successful study of energy transfer mechanisms between Yb3+ sensitizers and Ho3+, Er3+, Tm3+ activators.

Conclusions:

• The synthesized CaF2 UCNPs demonstrate high color purity and tunable emissions, suitable for advanced optical applications.
• The study highlights the potential of these UCNPs in security features, particularly in latent fingerprint detection.
• Lanthanide ion doping in CaF2 provides a versatile platform for developing novel upconversion materials.