Sensitized intrinsic phosphorescence from a poly(phenylene-vinylene) derivative

Intrinsic phosphorescence in a phenyl-substituted poly(phenytene-vinylene) (PhPPV) film sensitized by a phosphorescent dye dopant has been directly observed for the first time for PPV class conjugated polymers. Efficient triplet energy transfer from the platinum porphyrin dye molecules to the PhPPV polymer was found to occur as the triplet level of the dopant (1.91 eV) is above the triplet level of PhPPV, which was determined to be at 1.63 eV. Intrinsic phosphorescence emission has been observed at room temperature as well. A significant decrease in emission intensity of phosphorescence has been found, if the sample was measured in air indicating quenching of triplets by oxygen. (C) 2003 Elsevier Science B.V. All rights reserved

Triplet dynamics and charge carrier trapping in triplet-emitter doped conjugated polymers

Phosphorescent (Ph) properties and charge carrier trapping have been studied in conjugated polymer CNPPP with incorporated red-emitting Btp(2)Ir(acac) metal-organic complex by time-resolved photoluminescence and thermally-stimulated luminescence (TSL) techniques. We characterized intrinsic Ph of CNPPP matrix and dynamics of triplet excitations of Btp(2)Ir(acac) confined by the polymer host. Combined studies of time and intensity dependence of guest Ph have demonstrated that the observed decrease in the Ph efficiency in CNPPP:Btp(2)Ir(acac) system at increasing excitation intensity is dominated by mutual host-guest triplet-triplet annihilation. We observed Ph spectral diffusion effects at 10 wt.% of Btp(2)Ir(acac) dispersed in a polymer matrix, which is a proof for the triplet excitons migration though the manifold of triplet-emitter sites, and which governs the Ph concentration quenching effect. TSL measurements have provided direct evidence that the triplet-emitter molecules create a deep charge trap in the conjugated polymer and allowed trap characterization. (c) 2009 Elsevier B.V. All rights reserved.status: publishe

Pyroelectric luminescence via internal Poole-Frenkel effect

Pyroelectric luminescence is a universal property of pyroelectric materials under changing temperature. In all compounds studied, inorganic and organic, it has two possible manifestations: Short-emission bursts caused by discharge of the pyroelectric field through the surrounding atmosphere and a smooth luminescence slowly varying with temperature. This latter emission, characteristic for the specific material, still waits for an explanation. With \chem{Sn_2P_2S_6} as a sample pyroelectric we show that this luminescence arises from a release of trapped charge carriers, triggered by the pyrolectric field via the Poole-Frenkel effect

Exciton diffusion length and lifetime in subphthalocyanine films

Organic photovoltaic cells with chloro[subphthalocyaninato]boron(III) (SubPc) as donor in combination with buckminster fullerene (C60) as acceptor in a planar heterojunction configuration have shown high power conversion efficiencies. The parameter that determines the critical distance to the heterojunction over which light-generated excitons can be harvested is the exciton diffusion length. Here, we characterize this exciton diffusion length in SubPc thin films by photoluminescence (PL) quenching experiments in a planar bilayer system. As the layer thickness is much smaller than the optical penetration depth, we apply the transfer matrix method (TMM) to calculate the internal optical field inside the organic structures and use this to derive the intrinsic PL spectrum. An exciton diffusion length of 28 nm is determined, and good agreement is found with the diffusion lengths obtained from modeling the external quantum efficiency. In addition, time-resolved PL measurements are performed to determine the exciton lifetime to be 0.3 ns