Influence of the ionisation–recombination process on the fluorescence and lasing properties of complex molecules in the gaseous phase

Theoretical and experimental investigations are reported of the influence of the recombination of charged particles, formed as a result of multistage photoionisation of complex molecules in a buffer gas, on the fluorescence and lasing properties of molecules. It is shown that strong photoexcitation results in depletion of the S₁ state and additional filling of the T₁ state of molecules, which leads to a reduction in the intensity of the fluorescence emitted per unit volume and to a faster (compared with the liquid phase) fall of the fluorescence quantum efficiency when the rate of excitation is increased. The example of a gaseous-phase laser based on a mixture of 2,5-diphenylfuran and pentane is used to show that the appearance of additional internal losses in the active medium due to the process under investigation results in a serious deterioration of the energy characteristics of gaseous-phase lasers utilising complex molecules.