Anomalous Kinetics of Photoluminescence from Degrading Organic Materials and Its Theoretical Rendition

Photoluminescence (PL) degradation of thermally evaporated Alq3 thin films is described by four Kohlrausch-Williams-Watt (KWW) functions, which are solely mathematical expressions. The present contribution not only unfolds the physical meaning of the KWW function, but also reveals new mathematical tools. By introducing the concept of the material clock, the system has been described by a damped harmonic oscillator, which in certain conditions allows the expansion of the KWW function in the so-called Prony series. The terms of this series can be attributed to chemical and physical processes that contribute to the decay, i.e., the degradation, of the Alq3 thin films when interacting with internal and environmental agents. These insights unveiled the usefulness of proper mathematical procedures and properties, such as the monotonicity and the complete monotonicity, for investigating the PL of this ubiquitous organometallic molecule, which possesses one among the highest emission yield. Moreover, this method is also promising for describing the photoluminescent processes of similar organic molecules important both for basic research and optoelectronic applications.