Quantum Confinement Explains Pump-Dependent Luminescence from Butyl-Terminated Si Quantum Dots

The origin of the luminescence of colloidal organically terminated silicon quantum dots is the topic of prime importance both from a fundamental point of view and in terms of various applications. In order to shed light on this topic, one should find out whether the basic principles of a particular theoretical approach are coherent with the experimental spectra and characteristics of real specimens with their inevitable imperfections. In this work, we develop a phenomenological semi-analytical method that matches (i) photoluminescence (PL) spectra of silicon colloidal quantum dots, (ii) size distribution of quantum dots, and (iii) excitation source characteristics. The method is based on the (i) log-normal size distribution of quantum dots, (ii) shifted log-normal distribution of optically excited dots, and (iii) influence of quantum confinement on emission and absorption. The formalism has been applied for the analysis of experimental PL spectra of butyl-terminated silicon quantum dots (reported in Dohnalova et al. Light: Sci. Appl. 2013, 2, e47), and it allowed quantitative description of experimentally observed phenomena such as (i) the blue shift of the PL peak position and its 2-fold widening with an increase of excitation photon energy and (ii) enhancement of the interval between the PL peak and excitation photon energy. The analysis has shown that the PL properties of butyl-terminated Si quantum dots are defined by core excitons while the surface effects play a minor role in contrast to the case of Si dots embedded into silica.