Preparation Of Terbium,samarium Doped ZnO Quantum Dots And Its Spectrum Modulation Mechanism

ZnO quantum dots（QDs）are one of the great potential application materials,which have a wide band gap,strong UV absorption ability and are easy to be doped.Rare earth can provide a wide variety of choices for light emitting materials preparation,because they possess rich energy levels which can produce various absorption and emission of radiation.The lighting characteristics of ZnO QDs are well enhanced after doped with rare earth ions,which allows the successful application in solar glass cover.So further applying ZnO QDs in solar cells will improve the utilization of solar energy.In this paper,Tb³⁺doped,Sm³⁺doped and Tb³⁺/Sm³⁺co-doped ZnO QDs were prepared by the sol-gel method.The influence of doping concentration of terbium and samarium ions on structure,morphology and luminescence performance of ZnO quantum dots were analyzed.The energy transfer between ZnO matrix and terbium ions,ZnO matrix and samarium ions,terbium ions and samarium ions were discussed.Specific contents and results are as follows:（1）There was no influence to the crystalline phase of ZnO QDs after rare earth doped.XRD diffraction peaks appeared no other substances,only ZnO crystals were obtained.With the increase of terbium ions,samarium ion concentrations,the intensity of XRD diffraction peaks decreased,the angle of diffraction peaks first reduced and then shifted to higher angle,which responded to the size of ZnO QDs first decreased and then increased.The crystallinity of ZnO QDs reduced because of the crystal defects.（2）The TEM indicated that the morphology and size of ZnO QDs didn’t change a lot after rare earth ions doped.The average particle diameter were about 5nm.ZnO QDs were circular and had clear lattice.However,there was reunion phenomenon in the ZnO QDs.XPS proved the existence of Tb-O-Zn and Sm-O-Zn structure in the ZnO QDs.（3）When excitation wavelength was 485nm,Tb³⁺doped and Tb³⁺/Sm³⁺co-doped ZnO QDs achieved the light-emitting of Tb³⁺ions.When excitation wavelength was 472nm,Sm³⁺doped and Tb³⁺/Sm³⁺co-doped ZnO QDs achieved the light-emitting of Sm³⁺ions.When excitation wavelength was 325nm,ZnO QDs,Tb³⁺ions and Sm³⁺ions all achieved light-emitting.（4）With the increase of terbium ions,samarium ion concentrations,the luminous intensity of ZnO QDs first increased and then decreased.When doping concentration was more than 1%,Tb³⁺doped and Sm³⁺doped ZnO QDs occurred concentration quenching.When the concentration of Sm³⁺ions was 2%and the Tb³⁺ions was more than 1%,Tb³⁺/Sm³⁺co-doped ZnO QDs occurred concentration quenching.Compared to undoped ZnO QDs,the emission spectra appeared red shift after rare earth ions doped.（5）The energy transfer existed between ZnO matrix and Tb³⁺ions,ZnO matrix and Sm³⁺ions,Tb³⁺ions and Sm³⁺ions,respectively.The absorbed energy of ultraviolet light was transmitted from ZnO matrix to Tb³⁺ions and Sm³⁺ions,which achieved not only the self-luminescence of ZnO QDs but also the promotion of Tb³⁺ions and Sm³⁺ions visible light-emitting.The energy level pair of Tb³⁺ions ⁵D₄→⁷F₂matched well with Sm³⁺ions ⁴G_5/2→⁶H_9/2,so there was no cross-relaxation transfer phenomenon of non-radiative energy transfer.The efficient energy transfer of Tb³⁺ions enhanced the characteristic emission peak of Sm³⁺ions at 650nm significantly.