Hydrothermal Synthesis And Property Study Of Large Single Crystals Of Rare Earth Hydroxides

The main content of this thesis includes two parts.In the first part,the large single crystals of rare earth hydroxides[RE?OH?₃]were prepared by simple solid KOH assisted hydrothermal method.In order to obtain the large single crystals of[RE?OH?₃],a series of experiments were carried out to determine the optimum reaction conditions of hydrothermal synthesis.The structure and morphology of large single crystals were characterized and analyzed through powder X-ray diffraction?XRD?,4-circle single-crystal diffraction,X-ray photoelectron spectroscopy?XPS?,Fourier transform infrared?FTIR?spectroscopy and field emission scanning electron microscopy?FESEM?.The possible growth mechanism of large single crystals of RE?OH?₃ was also proposed.In the second part,the photoluminescence and magnetic properties of RE?OH?₃ species were studied.The results would provide the basis for the practical application of large single crystals of RE?OH?₃ as luminescent materials and magnetic materials.The main research results of the thesis were summarized as follows.1.Rodlike single crystals of Gd?OH?₃,Eu?OH?₃,La?OH?₃,Pr?OH?₃,Nd?OH?₃,Sm?OH?₃ and Tb?OH?₃ in the length of several millimeters have been successfully prepared by using solid KOH assisted hydrothermal method.The synthesis method is simple,and it may be used for the synthesis of other hydroxide crystals.Then the condition experiments were carried out by taking Gd element and Eu element as examples.The results show that the optimum reaction conditions were the reaction temperature 280 ?,the reaction time 7 days,initial reactant 1.5 mmol Gd2O3 or Eu2O3 solid and supersaturated KOH solution in which solid KOH was about 0.4 mol.The obtained products were characterized by XRD,four circle single crystal diffraction,XPS,FTIR and FESEM.The results indicated that all the large crystals were pure phase and crystallized well.The morphologies of large single crystals of Gd?OH?₃ and Eu?OH?₃ were close to hexagonal prism.In addition,the possible growth mechanism of large single crystals of RE?OH?₃ among which choosing Gd?OH?₃ as the representative was proposed.It is revealed that the excess KOH solid is important for the preparation of large single crystals of RE?OH?₃ in this paper.2.The photoluminescence properties of large single crystals of Gd?OH?₃ and Eu?OH?₃ were studied by X-ray fluorescence spectrometer and their magnetic properties were measured by a superconducting quantum interference device?SQUID?.The Gd?OH?₃ sample emitted ultraviolet light at 311 nm which belongs to narrow-band ultraviolet B?NB-UVB?under 273 nm excitation.NB-UVB has a certain effect on the treatment of skin diseases.Therefore,large single crystals of Gd?OH?₃ are expected to be applied to phototherapy lamps.Meanwhile,photoluminescence of the as-obtained Gd?OH?₃ species doped with Dy3+ or Sm3+ or Eu3+ was investigated.The magnetic properties of large single crystals and powder crystals of Gd?OH?₃ demonstrated that they are all paramagnetic materials.For large single crystals of Eu?OH?₃,Eu3+ has multiple emission bands in the visible region under 394 nm excitation.Under low magnetic field strength and high magnetic field strength,the magnetic properties of large single crystals of Eu?OH?₃ were different.They also had differences with that of microcrystals of Eu?OH?₃ as previously reported.The phenomenon may be due to the different sizes of crystals which needs further study.