Comment on “Optical characterization of quantum dots entrained in microstructured optical fibers” [Physica E 26 (2005) 377–381]

In a recent paper, K.E. Meissner, C. Holton, W.B. Spillman Jr. [Physica E 26 (2005) 377] presented a study of the optical properties of colloidal CdSe/ZnS core-shell quantum dots entrained in a microstructured optical fiber. In particular, the authors claimed to have observed optical gain in this system through tight evanescent coupling between a probe light in the core of the fiber and photo-excited quantum dots in the cladding. I suggest that there are fundamental reasons, which are well investigated experimentally and documented, why such quantum dots cannot exhibit optical gain phenomena under continuous-wave excitation, as the authors suggest, and that the experimental results and interpretation do not address these issues, nor do they adequately justify the conclusions reached.