CdS quantum dot surface defect emission for white light emitting diodes.

The application of quantum dots (QDs) in white LEDs (WLEDs) have been rapidly growing as a promising option to replace current illumination sources. Commonly in these devices, the band edge emission of the QDs is used, trying to eliminate emission associated to QD surface defects. However, a relevant contribution of the surface defect emission to the photoluminescence (PL) quantum yield in these nanostructures has been reported. In fact, it has been pointed out that surface state emission could also be used in the fabrication of WLEDs and some effort have been done to tune, increase and control it. However, the PL properties are still not well understood.

In this work, we report the synthesis of colloidal cadmium sulfide (CdS) QDs by a non-injection method at different temperatures. These QDs were optically characterized by PL and absorption spectroscopy. The PL bands, attributed to transition related to surface states, span in the visible region and a shift of the band maximum seems to appear a different extraction times. These interesting results indicate the possibility of use these QDs in down-conversion materials for WLED fabrication.