Delayed emission from organic mixed crystals: Phosphorescence spectrum of biphenyl guest-carbazole host mixed crystal

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Abstract
The phosphorescence spectrum of a biphenyl guest‐carbazole host mixed crystal with guest concentration 10−2 mole/mole has been investigated in the temperature range 15–90 °K. At 15 °K the spectrum consists of three superimposed spectra, the most intense one being that of biphenyl guest with the origin at 22 986 cm−1. The two other spectra have been attributed to emission from traps T1 and T2. Emission from shallow trap T1 has its origin at 24 572 cm−1 and that from deep trap T2 at 23 552 cm−1. A tentative vibrational analysis of the spectra has been made. It has been observed that at very low temperature the guest and the two traps are all populated. As the temperature is raised, the shallow trap T1 is depopulated and emissions from the deep trap T2 and the guest are observed. On further increase of temperature T2 is also depopulated and the emission is wholly of biphenyl.