Studies of the temperature dependence of the phosphorescence spectra and decay rates of aromatic carbonyl molecules in mixed organic crystals

The temperature dependence of the phosphorescence spectra, decay rates and the S 0 → T 2(3 nπ*) absorption spectra were studied for aromatic carbonyl molecules in mixed organic crystals. The energy separation, ΔET , between the 3 ππ* lowest excited triplet (T 1) states and the higher 3 π * states (T 2) was estimated for several systems from the temperature dependence of the phosphorescence spectra and decay rates. It was found that the decay rates of the aromatic carbonyl molecules in the mixed crystal systems studied are determined by (1) thermal population to the 3 nπ* states and (2) increased radiationless transition rates at higher temperatures.