Far-infrared spectroscopy of Cd1−xMnxS quantum dots

Abstract

Far-infrared reflectivity spectra, in spectral region 50–600cm−1 and temperature region 80–300K, of CdS and Cd1−xMnxS nanocrystals embedded in hexametaphosphate, are presented. The analysis of the far-infrared experimental reflectivity spectrum was made by the fitting procedure. The Maxwell–Garnet effective medium theory is used for modeling an effective dielectric function as well as to separate respond from nanoparticles.To analyze spectra in CdS ωTO(≈238cm−1) to ωLO(≈305cm−1) spectral region, quantized dipolar modes in a spherical isotropic material quantum dot (QD) are considered in the framework of a continuum model. As to the mechanical boundary conditions rigid sphere is concerned. Experimental far-infrared reflectivity spectra of our samples are in general agreement with the predictions of this model.Experimentally registered and through fitting procedure located features for CdS nanoparticles in spectral region below CdS ωTO at: ≈102cm−1, ≈135cm−1, ≈170cm−1 and ≈210cm−1 are associated to defect induced modes, especially to defects located near the surface of CdS QD. In region over CdS ωLO, modes are identified as multiphonons. In Cd1−xMnxS QD spectra new reflectivity peaks are at: ≈85cm−1, ≈110cm−1 and ≈180cm−1 in spectral region below CdS ωTO, ≈270cm−1 inside CdS ωTO–ωLO spectral region and ≈356cm−1 and ≈376cm−1 in region over CdS ωLO. First two registered modes are associated to both mass and force constant defects at the surface, and rest four modes are consequence of MnS phases present in the sample.