HYBRID ORGANIC-INORGANIC QUANTUM DOT WHITE LIGHT EMITTING DEVICES

Abstract

White light emission from solid-state light emitting devices is a challenging problem in the field of lighting technology. White light can be created by mixing red, green, and blue color lights in a proper ratio, but the resultant spectrum of such lights does not follow the spectrum of pure white light. Also, fabrication of such devices is very difficult due to their complex structure as well as the need of sophisticated systems. Inorganic semiconductor quantum dots (QDs), extensively used in light emitting devices because of their unique properties of band gap tunability, narrow emission width, and ease of fabrication, can be applied to resolve the issues by preparing a single emissive layer of graded band gap or white light emitting quantum dots (WQDs). In a quantum dot, quantum yield and average fluorescence lifetime which are the figure of merit and can be significantly affected by the change of shape and size of QDs. In this thesis, first, the effect of shape and size of quantum dots on quantum yield and average fluorescence lifetime have been analyzed with the help of trioctylposphine (TOP) capped cadmium selenide QDs. As the shape of QDs changes from spherical to ovoid (along with increasing size), the number of selenium atoms on the surface becomes higher which are not properly capped by the TOP resulting in a higher number of surface states. This causes an increase in non-radiative recombination resulting in lower quantum yield and average fluorescence lifetime.