Highly Luminescent CdTe Nanocrystals Synthesized in Aqueous Solution and Self-Assembled on Polyelectrolyte Multilayers

Abstract

CdTe nanocrystals have been synthesized in aqueous solution at 92oC under open-air conditions. During the reaction, aliquots of the samples were taken at different growth times and used to obtain their UV-Vis absorbance and photoluminescence spectra in order to estimate the nanocrystal size. The absorption peaks are located around 459 nm for 1 h, 478 nm for 2 h, 491 nm for 4 h, 532 nm for 7 h and 610 nm for 94 h of growth time. The mean nanocrystal size for these samples is 2 nm, 2.2 nm, 2.3 nm, 2.6 nm and 3.4 nm, respectively, according to the theoretical calculations of 1s1/2 – 1s3/2 excitonic transition. Finally, CdTe nanocrystals were assembled using layer-by-layer technique on glass substrates, using PDDA as cationic polyelectrolyte and negatively charged CdTe nanocrystals. The Raman spectroscopy shows that CdTe nanocrystals preserve the nanoparticle properties after being assembled.

Fabrication and photophysical studies of CdTe quantum-dots dispersed in SiO2 sonogel optical-glasses

“…The corresponding absorbance spectra are shown in Figure 2a and b. The absorbance spectra of the starting CdTe-QDs/H 2 O (Figure 2a) present broad and well defined bands around 500 nm; the sample with larger crystallite size (sample A) exhibit a smaller absorbance peak at 506 nm and a redshift in its maximum with respect to the absorbance peak of sample B (located at 494 nm), which is consistent with the preparation reaction time increase for aqueous samples (Gutiérrez-Lazos et al, 2010). Indeed, this red shift is usually observed in semiconductor nanocrystals and it has been attributed to the crystallite size increase (Brus, 1984).…”

“…allowing the luminescent Raman detection). Here, the Raman peaks located within the 130-145 cm −1 range can be assigned to CdTe tetrapods (LOM-T); whereas the Raman emissions detected within the 150-165 cm −1 interval can be precisely correlated to the LO modes of CdTe quantum dots (Gutiérrez-Lazos et al, 2010;De Paula et al, 1996). These LOM-Raman peaks can be only observed from slightly doped HSG-samples: from (1.5:0.5) to (1.9:0.1) dopant concentrations.…”

“…The CdTe nanocrystals were prepared from aqueous solutions of NaHTe and Cd 2 + (Gaponik et al, 2002a(Gaponik et al, , 2002b. The telluride ion precursor was prepared according to reference (Gu, Zou, Fang, Zhu, & Zhong, 2008;Gutiérrez-Lazos et al, 2010) under N 2 atmosphere. The Cd 2 + precursor was prepared by mixing CdCl 2 and TGA as stabilizer in deionized water, maintaining the Cd/TGA molar ratio and pH at 1:6 and 5, respectively; the pH being adjusted with 3 M NaOH aqueous solution.…”