Multiphoton processes of charge carrier generation in thianthrene crystals

• Published in: The Journal of chemical physics 1982-04, Vol.76 (7), p.3768-3773
• Main Authors: Samoć, Marek, Samoć, Anna, Williams, Digby F.
• Format: Article
• Language: English
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.443416

Photoconductivity in crystals of thianthrene has been studied by a standard dc method and by exciting with pulses of weakly absorbed light from a dye laser. The dc photoconductivity exited in the range 300–400 nm depends on the light intensity to the 1.5 power and is attributed to the interaction between singlet and triplet excitions. The S–T interaction coefficient is estimated to be 2×10−11 cm3 s−1. Pulsed photoconductivity in the range 450–640 nm, which follows a cubic light intensity dependence can be explained as arising from photoionization of two-photon produced singlet excitions. This hypothesis is corroborated by a comparison of the action spectrum of the two-photon absorption coefficient with that of the three-photon generation of charges. The photoionization cross section of a singlet excition is found to be ∼10−23 cm2. In the range 385–440 nm, the pulsed photocurrent depends on the square of the light intensity, where carrier generation occurs through the photoionization of triplets formed by a direct S0–T1 absorption or photoionization of singlets formed by absorption within the Urbach tail of the first absorption band.