Synthesis, growth mechanism, and photoluminescence property of hierarchical SnO₂ nanoflower-rod arrays: an experimental and first principles study

Upstanding SnO₂ nanorod arrays covered by hierarchical SnO₂ nanoflowers grow on the indium tin oxide (ITO) substrate through a direct hydrothermal method. Corresponding growth mechanism has been investigated along with the reaction time. The ITO substrate plays a role of seed layer and guides the nucleation of SnO₂ nanoflower-rod arrays (NFRAs), which promotes the SnO₂ crystal nucleation grow into nanorod arrays in the hydrothermal reaction. The photoluminescence (PL) spectrum of the obtained SnO₂ NFRAs architecture reveals that the oxygen vacancies (V_O) are major reasons of luminescence. In order to better understand the relationship between the V_O and the luminous mechanism, a first principles study is carried out. The calculation results based on the density functional theory (DFT) indicate the energy level of V_O with the three types of charge state (the ionization energy of the V_O ⁰ state, V_O ⁺ state, and V_O ²⁺ state in band gap are 0.15, 2.84, and 3.15 eV, respectively) in SnO₂ NFRAs architecture, which is in agreement with the PL spectrum.