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International Journal of Photoenergy
Volume 2008 (2008), Article ID 684196, 5 pages
http://dx.doi.org/10.1155/2008/684196
Research Article

Diffusion Enhanced Upconversion in Organic Systems

Department of Material Science, University of Milano-Bicocca, via Cozzi 53, 20125 Milano, Italy

Received 29 March 2008; Accepted 5 May 2008

Academic Editor: Mohamed Sabry Abdel-Mottaleb

Copyright © 2008 A. Monguzzi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The upconverted fluorescence generation in a solution of multicomponent organic systems has been studied as a function of the temperature to investigate the role of resonant energy transfer processes and of the molecular diffusion on the overall emission yield. The strong blue emission observed exciting the samples at 532 nm derives from a bimolecular triplet-triplet annihilation between 9,10 diphenylanthracene molecules, which produces singlet excited states from which the higher energy emission takes place. Diphenylanthracene excited triplet states are populated by energy transfer from a phosphorescent donor (Pt(II)octaethylporphyrin) which acts as excitation light harvesting. At low temperature, the experimental data on the efficiency of the transfer have been interpreted in the frame of a Dexter energy transfer in the Perrin approximation. At room temperature, the fast diffusion of the molecules has been found to be the main factor which affects the energy transfer rates and the overall photon upconversion efficiency.