Efficient photon upconversion at remarkably low annihilator concentrations in a liquid polymer matrix: when less is...

Area of Science:

• Materials Science
• Photochemistry
• Organic Electronics

Background:

• Triplet-triplet annihilation (TTA) upconversion is a promising method for converting lower-energy photons to higher-energy ones.
• Efficient TTA upconversion typically requires high concentrations of annihilator molecules, which can lead to self-quenching and reduced performance.

Purpose of the Study:

• To achieve efficient green-to-blue TTA upconversion at low annihilator concentrations.
• To investigate the role of photosensitizer phosphorescence lifetime in TTA upconversion efficiency.

Main Methods:

• Utilized a zinc tetraphenylporphyrin (ZnTPP)-based photosensitizer with a long phosphorescence lifetime (11 ms).
• Employed a viscous polymer matrix to host the photosensitizer and annihilator.
• Measured upconversion quantum yield at varying annihilator concentrations (600 μM and 3 mM).

Main Results:

• Achieved a 24.5% quantum yield for green-to-blue TTA upconversion at a low annihilator concentration of 600 μM.
• Demonstrated that a higher annihilator concentration (3 mM) resulted in a slightly lower quantum yield of 24%.
• The long phosphorescence lifetime of the ZnTPP photosensitizer was crucial for enabling efficient upconversion at low concentrations.

Conclusions:

• Efficient TTA upconversion is achievable at significantly lower annihilator concentrations than previously reported.
• Photosensitizers with long phosphorescence lifetimes are key to overcoming concentration-dependent limitations in TTA upconversion.
• This work opens avenues for developing more efficient and practical upconversion systems for various applications.