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Here we report investigation of red-shifted defect photoluminescence observed in two-dimensional colloidal cadmium selenide nanoplatelets. We used absorption, photoluminescence and photoluminescence excitation measurements to show that red-shifted photoluminescence bands are related directly to nanoplatelets and may originate from surface imperfections as well as be a result of interaction between different nanoplatelets in the solution. We also found that the defect photoluminescence may be easily altered by simple mechanical treatment, including sonication and stirring, thus disclosing the ways to control nanoplatelets emission over time.

The impact of irradiation with higher and lower quantum energy than that corresponding to the fundamental absorption band of CdSe nanoplatelets has been studied. We show that the irradiation wavelength and oxygen strongly influence the photoluminescence of nanoplatelets. We demonstrate also that irradiation of CdSe nanoplatelets dry layers leads to a reversible change in their photoluminescence quantum yield. Keywords: semiconductor nanoplatelet, excitonic luminescence, trap states, intermittent irradiation.