On the origin of stretched exponential (Kohlrausch) relaxation kinetics in the room temperature luminescence decay of colloidal quantum dots.

The non-exponential room temperature luminescence decay of colloidal quantum dots is often well described by a stretched exponential function. However, the physical meaning of the parameters of the function is not clear in the majority of cases reported in the literature. In this work, the room temperature stretched exponential luminescence decay of colloidal quantum dots is investigated theoretically in an attempt to identify the underlying physical mechanisms associated with the parameters of the function. Three classes of non-radiative transition processes between the excited and ground states of colloidal quantum dots are discussed: long-range resonance energy transfer, multiphonon relaxation, and contact quenching without diffusion. It is shown that multiphonon relaxation cannot explain a stretched exponential functional form of the luminescence decay while such dynamics of relaxation can be understood in terms of long-range resonance energy transfer to acceptors (molecules, quantum dots, or anharmonic molecular vibrations) in the environment of the quantum dots acting as energy-donors or by contact quenching by acceptors (surface traps or molecules) distributed statistically on the surface of the quantum dots. These non-radiative transition processes are assigned to different ranges of the stretching parameter ß.

Interactions and compatibility of 11 S globulin from Vicia faba seeds and sodium salt of carboxymethylcellulose in an aqueous medium.

This work studies specific interactions and compatibility between a legumin and a linear carboxylated polysaccharide using gel permeation chromatography, sedimentation analysis, SDS gel electrophoresis, viscometry and phase analysis measurements. It uses the system water/11 S globulin/CMC as a model. Carboxymethylcellulose (CMC) molecules are able to cause a partial dissociation of the protein, subsequent formation of soluble interbiopolymeric complexes and partial aggregation of the free non combined protein at room temperature and pH 6.0-6.5. The maximal binding of biopolymers is observed at their equimolar ratio. The decrease in temperature of the mixture from 293 to 277 K leads to formation of the complex coacervate. The increase in pH from 6.0 to 7.6 results in suppression of complex formation and manifestation of the phenomenon of thermodynamic incompatibility if the total concentration of biopolymers in the system exceeds the critical concentration of segregative phase separation.