Confirming the lattice contraction in CdSe nanocrystals grown in a glass matrix by Raman scattering

Abstract

This work gives the evidence of the lattice contraction in CdSe nanocrystals (NCs) grown in a glass matrix. The CdSe NCs were investigated by atomic force microscopy (AFM), optical absorption (OA), and Raman spectroscopy. The average size of CdSe NCs can be estimated by AFM images. Using the OA spectra and the effective-mass approximation, it was also possible to estimate the average sizes of CdSe NCs, which agree very well with the AFM data. These results showed that the CdSe NCs grow with increasing time of heat treatment. The blue shift of the longitudinal optical (LO) modes and surface optical (SO) phonon modes with an increase in the average radius of the NCs, shown in the Raman spectra, was explained by the lattice contraction in CdSe NCs caused by thermodynamic interactions at the interface with the host glass matrix.

Carrier Dynamics and Magneto-Optical Properties of Cd1-xMnxS Nanoparticles

“…Figure 1a shows that the undoped CdS QDs (x = 0.000) exhibit confinement energy ( conf E ) as indicated by the OA band peak at ~3.10 eV. From this value and using a confinement model based on effective mass approximation [12,[15][16][17][18], the mean QD radius R was estimated by the expression: Econf = Eg + (ħ 2 π 2 ⁄ 2 R 2 ) -1.8(e 2 ⁄ εR), where Eg is the bulk material energy gap, is the reduced effective mass, e is the elementary charge, and ε is the dielectric constant. From this, a mean radius of about R~2.0 nm was estimated for the CdS QDs, thus confirming strong size quantum confinement [16].…”

“…However, a recent study of thermal treatments on undoped CdSe QDs [12] embedded in this same glass matrix (SNAB) showed a much smaller redshift (~0.03 eV) when annealed for 6 h. Since CdSe and CdS structures display great similarities, as well as Cd1-xMnxS with dilute Mn-concentration, it is reasonable to assume that they have the same growth kinetic in the same glass matrix. Thus, the higher shift (~0.05 eV) observed in Cd0.900Mn0.100S QDs annealed for 6 h provides strong evidences that the observed higher redshift must also be ascribed to a decrease of the effective concentration of Mn 2+ incorporated to the dots, and this decrease takes place during the thermal treatment of the sample.…”

“…Cd1-xMnxS NPs were successfully synthesized in this glass matrix by adding 2[CdO + S] (wt % of SNAB), and x[Mn] (wt % of Cd), with x = 0.0, 0.5, 5.0, and 10 %. The synthesis method consists in a two sequential melting-nucleation approach, in which it is possible obtain ensembles of nearly spherical nanoparticles embedded in a glass matrix [12]. First, the powder mixture was melted in an alumina crucible at 1200 ºC for 30 minutes.…”

“…It is well known that the optical properties of NPs can be significantly changed by interactions between nanostructures and their host material, due mainly to the formation of surface defects [11,12]. These surface defects are heavily dependent on NP size and become more important with increasing surface-volume ratio.…”

Dilute magnetism in Zn1−xMnxTe nanocrystals grown in a glass template

“…Finally, as a result of the thermal annealing, dilute Zn 1Àx Mn x Te NCs were formed in the PZABP matrix. Other details on the nanoparticles growth in glass matrices by the fusion method can be found in literature [3,[13][14][15].…”