Continuous hydrothermal synthesis of ZnGa2O4:Mn2+ nanoparticles at temperatures of 300–500 °C and pressures of 25–35 MPa

Mn2+ doped ZnGa2O4 particles were continuously synthesized in subcritical and supercritical water using a flow hydrothermal reaction system. Zn, Ga and Mn nitrates were used as the starting materials. The syntheses were carried out at temperatures from 300 to 500 °C, at pressures from 25 to 35 MPa, at KOH concentration of 0.04 M, and for residence times from 0.13 to 1.13 s. X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric differential thermal analysis (TG-DTA) and photoluminescent spectroscopy were used to characterize the samples. Single phase of ZnGa2O4 was achieved at residence times of less than 1 s. The crystallite sizes were in the range from 12 to 21 nm which tend to increase with an increase in the reaction temperature and with a decrease in the reaction pressure. Green emission was observed for the annealed samples under reducing conditions whereas as-synthesized samples did not exhibit photoluminescence.

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► Hydrothermal flow reaction was successfully utilized to fabricate ZnGa2O4 nanocrystallites.
► Hydrothermal reaction of the mixture of Zn, Ga, and Mn nitrate aqueous solution with KOH solution at 300–500 °C was carried out less than 1 s.
► Solvent property such as density and dielectric constant of water affects crystal growth rate and crystallinity.
► ZnGa2O4:Mn green phosphor was achieved by annealed under reducing conditions.