Four-level system with two-quantum excitation. Dependence of luminescence on excitation

Abstract

1. In two-quantum excitation of a four-level system, a quadratic dependence on the intensity of the luminescence from high excited singlet states on the exciting radiation intensity is observed only in the absence of saturation of the first excited singlet state. 2. In the presence of saturation of the first excited singlet level it is impossible to establish unambiguously the dependence of the intensity of the luminescence from HSS on the excitation intensity. 3. Light quenching and resonance transfer of excitation energy have a noticeable effect on the form of the characteristic dependences. In this case even under conditions of saturation of the first excited singlet level the characteristic dependences of the luminescence from HSS are described by an order of the nonlinearity that is close to unity.