Synthesis And Optical Characteristic Studies Of Rare-earth Doped ZnO Nanoparticles

Doping is the effective way to improve the physical properties of semiconductors.Rare-earth doped nanocrystals have extensive application prospect in the preparationof integrated optoelectronic devices such as optical devices （blue, green, red）, as theyare of high efficient optical properties even though at room temperature. ZnO is akind of wide bandgap semiconductor luminescence material and it is quite a goodchoice to be matrix material for rare-earth doping modification. The rare-earth dopedZnO has new features different from eigen ZnO.Proper doping can improve its optical,electrical, magnetic and other properties, which applied in many aspects. Because ofthe different characteristics of the nanometer matesrials, researchers have been tryingto prepare rare-earth doped ZnO nanocrystals, and have gained a series ofachievements. However, the radius of rare earth ion is much larger than zinc ions, andthe valence states are not the same, it is difficult to dope rare earth ions into the ZnOlattice effectively.In this thesis, rare-earth ions, including Eu3+and Tb3+-doped ZnO nanoparticleswere prepared by solvothermal method. By adjusting the particle formation conditionsand the growth process, we had realized the controlled growth of the good crystallinerare-earth doped nanoparticles. We discussed the influnence on morphology, particlesize and optical performance of nanoparticles by changing the amount of rare-earthelement. Various measuring methods were used to characterize ZnO nanoparticles,such as powder X-ray diffraction（XRD）, scanning electron microscope（SEM）,transmission electron microscope（TEM）, raman spectroscopy and photoluminescencespectroscopy（PL）. We investigated the microstructure, optical properties, evolutionregularity and the relationship between material structure and properties. The resultsof the present study are listed as follows:1.With the solvothermal method, we obtained rregular spherical ZnO:Eu andZnO:Tb nanoparticles. The distribution of ZnO:Eu sample was between18²6nm,and ZnO: Tb sample was between18²8nm. Both of the doped ZnO crystals werehexagonal wurtzite structures, corresponding to the basical structures of pure ZnO.HERM pictures showed that Eu （or Tb） elements evenly distributed in the lattice ofZnO and no separate Eu2O3particles were found.When annealed at450℃, ZnOsamples appeared apparent lattice distortion phenomenon. Due to the different size of radius and the valence states, doping RE3+into ZnO will inevitably lead to seriouslattice distortion. It proved that the RE3+incorporated into ZnO lattice indeed.2. Doping can availably refine the grain size of the samples. Under the samepreparation condition,the size of Eu-doping nanoparticles decreased by12.45²7.20%,from20.64²7.32nm（pure ZnO） to18.07²2.98nm; while the Tb-dopingnanoparticles decreased by5.75¹5.94%, down to17.35²5.75nm. As annealingtemperature increasing, the size of sample particles increased and the uniformity gotworse. At the same time,the reunion phenomenon was more obvious. Rare-earthelments assemenbled on the surface of the sample when annealing at a hightemperature.3.The Luminescence properties changed a lot after doping rare-earth elements.On the basis of the original blue green, a weak red emission peak appeared. Thetransitions of⁵D₀â†'⁷F₁,⁵D₀â†'⁷F₂and⁵D₀â†'⁷F₀of Eu³⁺ ions can be found in PL spectra.Under the effect of laser fluorescence, we found the energy transfer process from ZnOto Eu3+. By observing the splitting phenomenon of fluorescence peaks, rare-earth ionsposition in the lattice had changed. When thermal-treatment temperature is450℃,three split peaks at about612nm were found in the ZnO:Eu sample which occuredLattice distortion. It reflected that the rare-earth ions occupied the C3symmetryposition of ZnO lattice. But when thermal-treatment temperature is700℃, thesplitting conditions of the sample was similar to Eu₂O₃. It illustrated the gradualseparation of Eu³⁺from the crystal of ZnO.