Fabrication and optical properties of ultrathin CdSe filaments incorporated into the nanochannels of fibrous magnesium silicates

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Abstract
CdSe has been synthesized in the nanochannels of the transparent fibrous magnesium silicates, namely chrysotile asbestos and sepiolite. The optical absorption spectra of CdSe confined in both matrices have been found to display a blue shift compared with bulk CdSe (about 0.14 eV for asbestos, and about 0.9 eV for sepiolite) and a strong polarization dependence. CdSe filaments with diameters 7 - 8 nm inside asbestos channels have been observed by transmission electron microscopy. Resonance Raman bands due to the LO phonon of CdSe filaments have been found, when the incident and scattered light are polarized along the filaments. Asbestos-confined CdSe filaments are considered as cylindrical quantum wires, which display a quantum size effect in the electron spectrum. The interpretation of the absorption spectra of the sepiolite-confined CdSe is more speculative. One possibility is the formation of CdSe filaments with diameters about about 3 nm in mesochannels of the sepiolite.