Upconversion Yb³⁺/Er³⁺:La₂Ti₂O₇ phosphors for solid-state lighting and optical thermometry

Area of Science:

• Materials Science
• Solid-state Chemistry
• Luminescence

Background:

• Lanthanum titanate (La₂Ti₂O₇) is a promising host material for phosphors.
• Doping with ytterbium (Yb³⁺) and erbium (Er³⁺) ions enables upconversion luminescence.
• Understanding the influence of pump power and temperature is crucial for practical applications.

Purpose of the Study:

• To synthesize and characterize Yb³⁺/Er³⁺ co-doped La₂Ti₂O₇ phosphors.
• To investigate the color tunability under varying pump power.
• To evaluate their potential for optical thermometry using the fluorescence intensity ratio technique.

Main Methods:

• Solid-state reaction synthesis of orthorhombic La₂Ti₂O₇ phosphors doped with Yb³⁺ and Er³⁺.
• Spectroscopic analysis of pump power and temperature dependencies.
• Application of the fluorescence intensity ratio (FIR) method for optical thermometry.

Main Results:

• Pump power significantly influences the emission color, transitioning from green to white upconversion.
• A two-photon transition mechanism is proposed for the upconversion energy transfer.
• The phosphors demonstrate effective optical thermometry with calculated sensitivities.
• Absolute temperature sensitivities decrease with increasing Er³⁺ concentration, with maximum values reported up to 0.64x10^-2 K^-1.

Conclusions:

• Yb³⁺/Er³⁺ co-doped La₂Ti₂O₇ phosphors offer tunable optical properties.
• These materials are suitable for optical thermometry applications.
• The study provides insights into upconversion mechanisms and material performance for sensing.