Understanding the thermometric behaviour of LiLuF₄:Tm³⁺,Yb³

Area of Science:

• Materials Science
• Nanotechnology
• Spectroscopy

Background:

• The Er³⁺, Yb³⁺ system is a well-established luminescent thermometer.
• The Tm³⁺, Yb³⁺ system offers potential for near-infrared thermometry but is less understood.
• Understanding Tm³⁺, Yb³⁺ thermometry is crucial for applications in medicine, nanoelectronics, and industry.

Purpose of the Study:

• To investigate the Tm³⁺, Yb³⁺ upconversion system for luminescent Boltzmann thermometry.
• To elucidate the influence of sample morphology (microcrystalline vs. nanocrystalline) and surface ligands on thermometry performance.
• To establish guidelines for optimizing Tm³⁺, Yb³⁺ based thermometers.

Main Methods:

• Utilized temperature-dependent multiphonon relaxation in Tm³⁺, Yb³⁺ doped LiLuF₄.
• Analyzed both micro- and nanocrystalline samples.
• Employed experimental studies combined with kinetic modeling.

Main Results:

• Tm³⁺, Yb³⁺ can act as a wide-range Boltzmann thermometer in ligand-free, microcrystalline samples with low host cutoff phonon energies (∼500 cm^-1).
• Nanocrystalline samples and surface ligands with high vibrational energies negatively impact thermometry performance.
• The Tm³⁺, Yb³⁺ system's performance is highly sensitive to the host material and sample structure.

Conclusions:

• Optimizing Tm³⁺, Yb³⁺ luminescent thermometers requires careful selection of ligand-free microcrystalline hosts with low phonon energies.
• The Tm³⁺, Yb³⁺ system shows promise but requires specific conditions to outperform established systems like Er³⁺, Yb³⁺.
• This study provides clear guidelines for the development and application of Tm³⁺, Yb³⁺ based upconversion thermometers.