Synthesis of CdS nanocrystals by a microwave activated method and investigation of the photoluminescence and electroluminescence properties

We have synthesized CdS nanocrystals (NCs) by a microwave activated method. CdSO₄ and Na₂S₂O₃ were used as the precursors and thioglycolic acid (TGA) was used as capping agent molecule. The aqueous synthesis was based on the heat sensitivity of Na₂S₂O₃. In this method, microwave irradiation creates the activation energy for dissociation of Na₂S₂O₃ and leads to the CdS NCs formation. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses demonstrated hexagonal phase CdS NCs with an average size around 3 nm for sample prepared at 5 min irradiation time. A band gap range of 3.38-2.89 eV was possible only by increasing the microwave irradiation time, corresponding to a 2.7-3.7 nm size. Photoluminescence (PL) spectra showed a white emission between 400 and 750 nm. The best attained PL quantum yield (QY) of the NCs was about 10%. Synthesized NCs were used as emissive layer in a light emitting device (LED) with ITO/PEDOT:PSS/PVK/CdS-NCs/AL structure. Turn on voltage of fabricated device was about 7 V. The CIE color coordinate of the LED at (0.34, 0.43) demonstrated a near white light LED with an emission on green-yellow boundary of white.