Diffusion Enhanced Upconversion in Organic Systems

A Monguzzi,F Meinardi,R Tubino

doi:10.1155/2008/684196

A Monguzzi, F Meinardi + Show 1 more

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https://doi.org/10.1155/2008/684196

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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.

Highlights

The well-known upconversion processes such as secondharmonic generation or two-photon absorption usually require very high excitation power densities [1], typically of the order of MW/cm2, being effective only by using laser sources
A novel approach has been proposed based on the exciton triplet-triplet annihilation (TTA) between organic molecules, which gives rise to an upconverted fluorescence indirectly excited via energy transfer (ET) from a second molecular species acting as a light harvesting [2,3,4,5,6,7]
The upconverted light is the result of several intermediate photophysical processes: (i) absorption of the excitation light by a phosphorescent donor (D) molecule producing triplet excited states; (ii) energy transfer processes towards metastable triplet state of an acceptor molecule (A); (iii) triplet-triplet annihilation giving rise to high-energy singlet excited states of the second species, from which the upconverted fluorescence takes place

Summary

INTRODUCTION

The well-known upconversion processes such as secondharmonic generation or two-photon absorption usually require very high excitation power densities [1], typically of the order of MW/cm, being effective only by using laser sources. A novel approach has been proposed based on the exciton triplet-triplet annihilation (TTA) between organic molecules, which gives rise to an upconverted fluorescence indirectly excited via energy transfer (ET) from a second molecular species acting as a light harvesting [2,3,4,5,6,7] In such a way, the requested power density to have upconverted photons is reduced to the level of the solar emission (as low as ≈ 0.1 W/cm2) [5].

EXPERIMENTAL

RESULTS AND DISCUSSION

77 K 300 K

CONCLUSIONS