The well aligned poppy-flower-like SnO₂ nanoflower array on Sn-foil was successfully prepared by a simple solvothermal method without using any template or catalyst. The mixed solvent of aqueous sodium hydroxide and hydrazine hydrate plays a significant role for obtaining the crystalline pure SnO₂ nanoflower array. Each petal of the nanoflower consists of the (110) plane of SnO₂. The growth of the SnO₂ nanoflowers has been described by the formation of layered Sn-hydrazine complexes. The surface defects and the oxygen vacancies of the SnO₂ hierarchical nanoflowers are identified by Raman and electron paramagnetic resonance (EPR) spectroscopy and are analyzed in detail by steady state and time resolved photoluminescence spectra.