On the decay time of upconversion luminescence

Area of Science:

• Materials Science
• Physical Chemistry
• Luminescence Spectroscopy

Background:

• Upconversion luminescence (UCL) is crucial for various photonic applications.
• Understanding UCL decay dynamics is essential for optimizing material performance.
• Existing models often simplify the complex temporal responses observed in UCL.

Purpose of the Study:

• To systematically investigate the decay characteristics of UCL under anti-Stokes excitation.
• To elucidate the contributions of sensitizer lifetime, energy transfer, and cross-relaxation to UCL decay.
• To determine conditions under which UCL decay approximates the intrinsic lifetime of the emitting state.

Main Methods:

• Numerical simulations using rate-equation models.
• Systematic investigation of anti-Stokes excitation decay profiles.
• Analysis of factors influencing UCL temporal response.

Main Results:

• UCL decay profiles are complex, reflecting the entire upconversion system's response, not just the emitting state's lifetime.
• Sensitizer lifetime, energy transfer, and cross-relaxation significantly impact UCL decay.
• UCL decay time approximates the intrinsic lifetime only under specific conditions (short sensitizer lifetime, no cross-relaxation).

Conclusions:

• UCL decay dynamics are governed by a combination of processes.
• Stokes excitation is generally preferred for accurate intrinsic lifetime determination.
• High doping levels and cross-relaxation can complicate decay analysis and affect lifetime measurements.