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Influence of temperature on low-power upconversion in rubbery polymer blends
Tanya N Singh-Rachford1, Joseph Lott, Christoph Weder
1Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio, 43403, USA.
Journal of the American Chemical Society
|August 5, 2009
Summary
Temperature-dependent upconversion in polymer hosts was studied. Heating above the glass transition temperature (T(g)) enabled blue light emission via triplet-triplet annihilation (TTA), which was reversible until thermal degradation occurred.
Area of Science:
- Photochemistry and Materials Science
- Investigating photophysical processes in polymer matrices.
Background:
- Upconversion luminescence allows generating higher energy photons from lower energy ones.
- Palladium(II) octaethylporphyrin (PdOEP) acts as a triplet sensitizer, and 9,10-diphenylanthracene (DPA) as a triplet acceptor/annihilator.
- Polymer hosts with low glass transition temperatures (T(g)) are crucial for temperature-responsive photophysical behavior.
Purpose of the Study:
- To investigate the temperature-dependent upconverting properties of a PdOEP/DPA dye cocktail in various low T(g) polymer hosts.
- To understand the mechanism of sensitized triplet-triplet annihilation (TTA) and its relation to polymer matrix dynamics.
- To determine the thermal stability and reversibility of the upconversion process.
Main Methods:
- Utilizing selective excitation of PdOEP at 544 nm to induce anti-Stokes blue emission from DPA.
- Examining the dependence of upconverted fluorescence intensity on incident light power (quadratic relationship).
- Monitoring upconversion efficiency across a range of temperatures, including below and above the T(g) of polymer hosts like EO-EPI, Texin, and Tecoflex.
Main Results:
- Upconversion was suppressed below T(g) but clearly visible upon heating to room temperature.
- Upconverted emission intensity increased with temperature and was reversible for heating-cooling cycles below 400 K.
- Above 400 K, irreversible material failure prevented further upconversion.
- Phosphorescence decay analysis in Tecoflex EG-80A showed increased system heterogeneity with temperature (lower KWW beta values).
Conclusions:
- The T(g) of the polymer host critically controls the temperature-dependent upconversion via TTA.
- The reversible nature of the upconversion process offers potential for temperature-responsive photonic materials.
- Thermal stability limits the operational temperature range, with degradation occurring above 400 K.
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