Differential tunability effect on the optical properties of doped and undoped quantum dots

Abstract

We have studied the optical properties of size-tunable undoped and Mn 2þ -doped cadmium telluride (CdTe) quantum dots (QDs) of monodisperse suspensions with emission wavelength varying between 500 and 680 nm. The role of the surface is investigated for obtaining size-tunable, bright, and stable CdTe QDs. Differentially tunable optical properties of doped and undoped CdTe QDs has been reported. Unlike the continuous redshifting in the absorption spectra of pristine CdTe system, an unusual blueshift is observed for doped CdTe system after a certain time period of refluxion, followed by again a redshift and the disappearance of earlier peak with further refluxing. The available size range and optical properties are significantly controlled through Mn 2þ doping. The surface adsorbed Mn promotes ripening of the doped system as well as disintegration into smaller fraction after saturation in growth occurs. An optimum size fraction is identified for both the systems based on their photoluminescence (PL) quantum yield. The photophysics of Mn 2þ -doped nanocrystals has been proposed.

Aqueous synthesis of highly stable CdTe/ZnS Core/Shell quantum dots for bioimaging

“…In previous studies, multiple absorption peaks have been reported by several groups. They noticed that there was a decrease in the intensity of the initial peak in the absorption spectra with increase in the refluxing time that finally disappeared and that they attributed to disintegration followed by saturation in growth . In the present case we found a similar kind of behavior, in which the appeared hump at the short wavelength was almost fixed at the same wavelength, this may be due to the discontinuous growth of the ZnS shell over the CdTe core.…”

Macromolecular Systems with MSA-Capped CdTe and CdTe/ZnS Core/Shell Quantum Dots as Superselective and Ultrasensitive Optical Sensors for Picric Acid Explosive

“…CdTe-MSA quantum dots were synthesized at pH 8 and collected after 1 h, as reported earlier. 33 MSA-capped CdTe/ZnS core/shell quantum dots were synthesized by a one-pot approach 34 in addition to an extra step for the shell formation over the core QD. At first, 3 mM CdCl 2 , 0.75 mM Na 2 TeO 3 , and 9 mM MSA solutions were mixed with a buffer containing borax and citric acid.…”

A water–ethanol phase assisted co-precipitation approach toward high quality quantum dot–inorganic salt composites and their application for WLEDs

“…7(a), which could be attributed to the fact that the degradation of the ligands caused by UV irradiation increased the Cd dangling bond present on the surface of QDs that acted as the surface defect state. 34,37 As shown in Fig. 7(b), CdTe QDs were aggregated and totally precipitated after 48 h UV irradiation.…”

“…where λ is the wavelength of the first excitonic absorption peak. 34 It could be observed that as the size increases, the PL peaks of CdTe QDs were red-shifted from 519 nm to 629 nm, in which CdTe QDs emitting at 572 nm (size 3.0 nm) exhibit the highest PLQY of 26%. The color emission of the CdTe@NaCl powders covers from green (535 nm) to red (644 nm) with the highest PLQY of 23% at the emission wavelength of 598 nm.…”

“…A red shift of the PL maximum could be observed in CdTe@NaCl powders compared with CdTe QDs dispersed in water, which might be attributed to the changes of the dielectric constant of the surrounding media as well as by reabsorption of the blue part of the spectrum in optically dense samples. 34,35 No broadening of the full width at half maximum (FWHM) suggests that no aggregation of the CdTe QDs in the NaCl matrix occurs. The as-prepared CdTe@NaCl powders show a slight tint of colors under daylight while exhibiting strong size-dependent photoluminescence under UV light, as shown in Fig.…”