For your Q, I recommend you to read a ref. by Peng et al. ( W. W. Yu, L. Qu, W. Guo and X. Peng, Chem. Mater., 2003, 15, 2854.). Briefly, you can determine the size of CdTe QDs by UV-vis spectrum, then calculate the concentration of QDs. If any questions more, welcome to send e-mail to me. (sally208@ciac.jl.cn). Good luck!