Spectroscopic investigation of defect-state emission in CdSe quantum dots

CdSe quantum dots are the most studied Cd-based quantum dots with their high quantum yield, high photostability, narrow emission band, and easy synthesis procedure. They are frequently used to develop light emitting diode (LED) due to their unique photophysical properties; however, their narrow emission band causes a challenge to design white LEDs because white light emission requires emission in multiple wavelengths with broad emission bands. Here in this study, we developed CdSe quantum dots with a narrow band-edge emission band and broad defect-state emission band through a modified two-phase synthesis method. Our results revealed that defect-state emission is directly linked to the surface of quantum dots and can be excited through exciting surfactant around the quantum dot. The effect of surfactant on emission properties of CdSe quantum dots diminished upon growing a shell around CdSe quantum dots; as a result, surface-dependent defect-state emission cannot be observed in gradient heterogeneous alloyed CdS_xSe_1-x quantum dots.