One of the most remarkable characteristics of single-walled carbon nanotubes (CNT) is their diversity of well-defined electronic and optical properties. Each CNT is composed of covalently bonded carbon atoms forming an ordered tubular structure with a specific diameter and roll-up angle. Depending on these two parameters, a CNT can be either metallic or semiconducting, the latter being very promising for optoelectronic and light-emitting applications.Unfortunately, there are specific intrinsic physical processes that make the fluorescence quantum yield of photoexcited CNTs rather low (<1%). In this talk I will discuss these processes and argue that covalent sidewall functionalization (e.g., oxygen doping) of CNTs can in principle suppress them all, thus dramatically increasing fluorescence intensity. Using the combination of various spectroscopic techniques and theoretical/computational tools, we have obtained a preliminary understanding of the exciton relaxation dynamics in covalently functionalized CNTs. For example, a combination of experimental observations of time-resolved fluorescence and kinetic modeling have allowed us to reveal and quantify a rich exciton relaxation dynamics. Temperature-dependent photoluminescence and photon-correlation experiments and their theoretical analysis will also be presented. The obtained insight has a promise of “unlocking” predictive design of highly luminescent CNTs for various applications.