Size-Tunable Solvothermal Synthesis of Zn2GeO4:Mn2+ Nanophosphor in Water/Diethylene Glycol System

Zn2GeO4:Mn2+ nanophosphors are synthesized from germanium(IV) oxide and acetates of zinc and manganese(II) in a mixed solvent of water and diethylene glycol (DEG) by the solvothermal reaction at 200 degrees C for 2h. Phase pure Zn2GeO4:Mn2+ is obtained for the samples prepared at 0 <= x(DEG)<= 91.7, where x(DEG) is the volume percentage or DEG in the mixed solvent. The particle and crystallite sizes decrease with the increase in x(DEG). The sample prepared at x(DEG) = 91.7 comprises the nanorods with 30.2 and 12.2 nm in mean length and width, respectively. The actual Mn concentration measured by X-ray fluorescence analysis increases with the increase in x(DEG) and approaches to the nominal concentration, 2.0 at %. The samples show green luminescence corresponding to the d-d transition of Mn2+ under the irradiation of UV and near-UV light. The photoluminescence intensity reaches a maximum around x(DEG) similar to 80. This is attributed to the competitive factors, the Mn concentration and the sizes of crystallites and particles.