3:30 PM - 3:45 PM
△ [14p-311-9] Triplet exciton diffusion via imaging of upconversion emission in molecular crystals
Keywords:Photochemistry, Photon upconversion, Triplet exciton diffusion
Photon up-conversion (UC) materials which convert low-energy photons to high-energy ones are expected to improve the conversion efficiency of solar cells. UC materials using triplet-triplet annihilation process consist of donor molecules and acceptor molecules. Solid state photon upconversion (UC) materials can potentially be used on the solar cells because of the appearance of UC emission under low excitation intensity. In order to improve the efficiency of UC under low excitation intensity, it is important to extend triplet exciton diffusion length of acceptor molecules because triplet exciton diffusion is inverse proportional to excitation threshold. Therefore, the method to measure triplet exciton diffusion length exactly is needed. However, conventional method to measure diffusion length is indirect method and not good for solid state UC materials due to its non-homogeneity. Therefore, the method to measure diffusion length directly is desirable.
In this study, 9,10-diphenyl anthracene or anthracene were used as an acceptor. Pt (II) Mesoporphyrin IX (D1) as a donor together with Mesoporphyrin IX- dihydrochloride (FD) as a fluorescence dye were adsorbed on alumina nanoparticles (30 nm) and these were used as hybrid donor particles (HDPs). The HDPs were doped in polycrystals of the acceptor molecule prepared on a glass substrate by spin-coating from tetrahydrofuran solution. 532 nm irradiation light is absorbed by D1 as well as by FD in the HDP. The excited states in FD generate fluorescence which is used to determine the location of each HDP. The excited state in D1 undergoes efficient intersystem crossing and the excitation energy is transferred to the acceptor via triplet-triplet (T-T) energy transfer. Thus generated triplet excitons of the acceptor diffuse, encounter each other and can undergo triplet-triplet annihilation which results in the generation of the UC photons. Due to diffusion of the triplet excitons of acceptor molecules, the UC photons can be emitted away from the HDP. As a result, the size of a microscopic image of UC emission can be larger than that of emission from the HDP, as determined from the size of fluorescence image of FDs attached to the HDP. The UC and fluorescence images from the samples were obtained using epi-illumination microscope and detected simultaneously on a CCD camera using an image splitter.
This novel technique is expected to provide novel insight into the triplet diffusion mechanism in UC materials.
In this study, 9,10-diphenyl anthracene or anthracene were used as an acceptor. Pt (II) Mesoporphyrin IX (D1) as a donor together with Mesoporphyrin IX- dihydrochloride (FD) as a fluorescence dye were adsorbed on alumina nanoparticles (30 nm) and these were used as hybrid donor particles (HDPs). The HDPs were doped in polycrystals of the acceptor molecule prepared on a glass substrate by spin-coating from tetrahydrofuran solution. 532 nm irradiation light is absorbed by D1 as well as by FD in the HDP. The excited states in FD generate fluorescence which is used to determine the location of each HDP. The excited state in D1 undergoes efficient intersystem crossing and the excitation energy is transferred to the acceptor via triplet-triplet (T-T) energy transfer. Thus generated triplet excitons of the acceptor diffuse, encounter each other and can undergo triplet-triplet annihilation which results in the generation of the UC photons. Due to diffusion of the triplet excitons of acceptor molecules, the UC photons can be emitted away from the HDP. As a result, the size of a microscopic image of UC emission can be larger than that of emission from the HDP, as determined from the size of fluorescence image of FDs attached to the HDP. The UC and fluorescence images from the samples were obtained using epi-illumination microscope and detected simultaneously on a CCD camera using an image splitter.
This novel technique is expected to provide novel insight into the triplet diffusion mechanism in UC materials.