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We have studied the influence of electric field and humidity on photoconductivity and fluorescence in particles of highly photoconductive Y-form TiOPc dispersed in a poly(vinylbutyral) polymer matrix. Both integrated and time-resolved fluorescence quenching by electric field were measured. Integrated fluorescence quenching showed a linear dependence at low applied fields and a linear correlation with carrier generation efficiency. Time-resolved fluorescence decays were analyzed by fitting the data to a sum of two exponentials representing fast and slow fluorescence components. Qualitative features of fluorescence decay were the same for low and high humidity levels. The amplitude and lifetime changes of the two fluorescence components upon the application of the electric field are in agreement with theory which describes energy transfer between free and trapped exciton states. These results indicate that carrier generation in Y-TiOPc originates from both relaxed and nonrelaxed intrinsic excited singlet states, while the trapped excitons do not lead to significant carrier production. The field dependence of integrated fluorescence quenching supports the existence of a carrier precursor state with charge-transfer character.

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The effect of electric fields on the fluorescence decay of block-copolymers containing poly(pphenylenevinylene) (PPV) and polynorbornene (polyNBE) was measured. Electric fields of up to 200 V/µm do not perturb the fluorescence decay profiles when the average size of the PPV block is small (i.e., PPV 3 -block-polyNBE 200 or PPV 3 -block-polyNBE 25 ). It appears that for short isolated PPV segments the electric field accessible for these studies does not allow dissociation of photogenerated excitons into electron-hole pairs. For larger PPV segments, as in PPV 20 -block-polyNBE 200 , the electric field reduces considerably the fluorescence lifetime and quantum yield. In addition, irradiating the sample under an electric field changes permanently its fluorescence characteristics. Control experiments show that neither irradiation nor the field alone can degrade the polymer.

We have studied the influence of electric field on fluorescence in particles of photoconductive TiOPc (I), TiOPc (IV), HOGaPc, and x-H2Pc dispersed in a polymer matrix. Electric field induced quenching of both the integrated and time-resolved fluorescence were measured. Time-resolved fluorescence decays were analyzed by fitting the data to a sum of two exponentials, representing the fast and slow fluorescence components. For HOGaPc, TiOPc(I), and TiOPc (IV), the fast fluorescence component exhibits both amplitude and lifetime quenching. These results indicate that carrier generation in HOGaPc, TiOPc(I), and TiOPc (IV) originates from both relaxed and nonrelaxed intrinsic excited singlet states, while the trapped excitons do not lead to significant carrier production. In contrast, for x-H2Pc, significant amplitude quenching of the fast component is observed only at high field, and the trapped excitons are an important source of photogenerated carriers. This indicates that x-H2Pc possesses at least some bulk-sensitized photocarrier generation. All of the phthalocyanines studied exhibited a quadratic dependence of integrated fluorescence quenching on electric field, indicating the existence of a neutral carrier precursor state.

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Scanning electron microscopy (SEM) is ubiquitous for imaging but is not generally regarded as a tool for thermal measurements. Here, the temperature dependence of secondary electron (SE) emission from a sample's surface is investigated. Spatially uniform SEM images and the net charge flowing through a sample were recorded at different temperatures to quantify the temperature dependence of SE emission and electron absorption. The measurements also demonstrated charge conservation during thermal cycling by placing the sample inside a Faraday cup to capture the emitted SEs and back-scattered electrons from the sample. The temperature dependence of SE emission was measured for four semiconducting materials (Si, GaP, InP, and GaAs) with response coefficients found to be of magnitudes ∼100−1000 ppm/K. The detection limits for temperature changes were no more than ±8°C for 60 s acquisition time.