Reply to the ‘Comment on ““Where does the fluorescing moiety reside in a carbon dot?” – Investigations based on fluorescence anisotropy decay and resonance energy transfer dynamics”’ by H. C. Joshi, Phys. Chem. Chem. Phys., 2019, 21, DOI: 10.1039/c9cp00136k

Abstract

The claim that the analysis regarding resonance energy transfer should have been made using different equations than those that we have used is negated based on the following points: (1) we are well aware of the equations the author has provided in his comment. The equation (eqn (3) mentioned below) that the author has written is undoubtedly too simple to describe the complex system delineated in our original paper. This particular equation is perhaps OK for simple dye (donor and acceptor) systems; however, such a simple equation is never enough for nanoparticle/quantum dot systems. (2) Another equation suggested by the author in his comment (eqn (2)) contains a parameter called donor concentration in excited state. We have categorically described in page 6–7 of our original paper why it is difficult to measure the donor concentration accurately even in the ground state. When the donor concentration can't be known accurately it can't be used in the suggested equation. (3) Donor–acceptor distance calculated by eqn (3)/Table 1 provided by the author deviates more than 100% from the distance that is physically feasible. Such kinds of problems are well documented in the literature. (4) One of the papers cited by the author in his comment and many other published papers clearly mention that in the case when all donor molecules/particles do not take part in the resonance energy transfer process or the stoichiometry of a donor–acceptor complex is not known or deviates strongly from 1 : 1, especially in quantum dots or any other nanomaterial system, it is not possible to extract accurate dynamical information related to RET from donor decay. Instead risetime of acceptor yields much more accurate information. Such situations do arise in our system as well.