Phononic, photonic and excitonic properties of ∼5 nm diameter aligned CdSe nanowires

The first work on quantum-sized CdSe nanowires (NWs) was made with NWs encapsulated in chrysotile asbestos nanotubes (asb-CdSe-NWs) in 1997. However, asb-CdSe-NWs remain under-investigated compared to widely-known solution-based CdSe NWs. Here, we study ∼5 nm diameter asb-CdSe-NWs aligned along their c-axis. Polarized optical absorption, Raman and photoluminescence spectra (OAS, RS and PLS) of asb-CdSe-NWs are examined. All spectra display a high anisotropy mainly associated with the anisotropic nearly cylindrical shape of NWs and dielectric contrast between NWs and asbestos, NW-light interaction being strong for the E//c and weak for E⊥c light polarizations. Asb-CdSe-NW E//c OAS shows ∼1.93 eV and ∼2.38 eV bands of excitonic transitions between size-quantized electronic states. RS display strong longitudinal-optical-phonon band with a weak surface-mode shoulder resonantly enhanced at the excitation wavelength corresponding to the ∼2.38 eV absorption band related to the 1Π1/2→1Πe transition. Acoustic radial breathing mode is observed at ∼14 cm−1. Low-excitation PLS show polarized exciton emission band at ∼1.883 eV while high-excitation PLS display ∼1.836 eV biexciton emission band. The ∼47 meV biexciton binding energy is enhanced due to the low-permittivity environment. Our asb-CdSe-NW results make an important complementary contribution to the studies of CdSe NWs fabricated by a variety of different techniques. •∼5 nm diameter aligned CdSe nanowires (NWs) are formed in asbestos nanotubes.•NW quantized exciton absorption bands are found at 1.93 and 2.38 eV.•NW Raman spectra show LO, surface and confined acoustic phonon bands.•NW luminescence spectra display 1.883 eV exciton and 1.836 eV biexciton bands.•NW optical anisotropy is due to the shape and dielectric contrast with matrix.