Hydrothermal synthesis and luminescent properties of microtubes constructed by fluffy Zns:Mn ²⁺ with nanostructures

Tubular micrometer-sized ZnS:Mn ²⁺ constructed by fluffy nanostructures were fabricated in the mixed solutions of water and ethanol in a fixed volume ratio with the aid of ethylenediamine. In the X-ray diffraction pattern, the products obtained in the presence and absence of ethylenediamine show the wurtzite and sphalerite phases, respectively. Field-emission scanning electron microscopic images reveal the evolution process from nanowires to fluffy ZnS:Mn ²⁺ to microtubes with the reaction times of 2, 4, and 8 hours at 100°C, and the basal nanowires are below 10 nm in diameter. Photoluminescence and photoluminescence excitation spectra were investigated. The results suggest that the wurtzite phase, instead of the sphalerite phase ZnS:Mn ²⁺ is luminescence-active for the ⁴T ₁- ⁶A ₁ transition of the Mn ²⁺ in the ZnS host. The excitation spectra monitored at orange emission bands exhibit sharp peaks at 320, 326 and 327 nm with increasing reaction times of 2, 4, and 8 hours, respectively, indicating the energy transfer from ZnS host to Mn ²⁺ ions, and the blue-shifts compared with the band gap absorption of the bulk counterpart (344 nm) are also observed due to the quantum confinement effects. The formation mechanism of the wurtzite one-dimensional nanostructures at such a low temperature is proposed based on a molecular template mechanism involving the bidentate coordinating ligand, ethylenediamine, and the possible formation mechanism of novel tubular structure are also discussed.