Fluctuations as a source of new physical properties of ultra-small CdSe nanoparticles

Abstract

The presence the static mean-square displacement of atoms from the equilibrium position caused by the structural defects can lead to the order-disorder transition in the ultra-small nanoparticles (USNs). It is shown that after the appropriate choose of the order parameter, the Landau mean-field theory can be used to describe this transition in USNs. In present article, the fluctuations of the order parameter are considered by statistical methods. The order-disorder transition in USNs is accompanied by large fluctuations of the order parameter. The order parameter changes continuously around its equilibrium value. This dynamic state of USNs can be considered as a new state of matter at the nanoscale, which is characterized by a continuous change of the order parameter. For the first time, the Landau theory is applied to describe the white-light emitting of USNs. It is shown that the fluctuations nearby the order-disorder transition are responsible for the white-light emission and that the emission spectrum has a crossover between the monochromatic and white-light emission at the critical nanoparticle diameter. Methods for controlling USNs properties by changing the order parameter are presented for the first time. The present theory gives a new approach to explain the white-light emission by CdSe quantum dots. It also follows from the present theory that the crossover can be suppressed (or shifted to a region of smaller nanoparticles) by an artificial change of the order parameter. The developed theory gives a new approach to predict the physical properties of USNs.