| Exploring the potential application value of new structure materials plays an important role in the development of materials science.New inorganic upconversion nanomaterials have broad application prospects in the fields of biomedicine,solar cells,three-dimensional displays,optical sensors,security encryption and anti-counterfeiting,information storage,and photoconductive switches,and upconversion single crystal materials can be used as all-solid-state lasers.Through the upconversion luminescence mechanism,the working substance can directly generate a new wavelength laser shorter than the pump wavelength,which can promote the miniaturization and application range expansion of all solid-state lasers,and promote the development of laser technology.Langbeinite-type phosphate material has a unique cage structure,and has high structural stability,thermal stability and chemical stability,strong radiation resistance,low thermal expansion,ion conductivity and other excellent physical and chemical properties.Therefore,such structural compounds have extremely high research value as upconversion luminescent host materials.On the one hand,this thesis explored the growth of langbeinite-type Rb2Ti2-xYbx(PO4)3 single crystals by the flux method,and on the other hand the preparation of A2TiYb(PO4)3(A=Rb,K)microcrystalline materials by the high temperature solid phase method.We used X-ray photoelectron spectroscopy and other techniques to study the structure of the crystal material,and characterize its up-conversion luminescence performance.The main research content and results of this paper are as follows:(1)The new langbeinite-type Rb2Ti2-xYbx(PO4)3(x=0.91?1.19?1.25)crystals were grown using the flux method,and the phase,crystal structure,electronic structure,and upconversion luminescence properties of the materials were characterized.As the concentration of doped Yb3+ions increases,the color of the crystals change from light blue to dark blue.The structure of the crystals belongs to the cubic crystal system,space group P213.X-ray photoelectron spectroscopy studies showed that with the increase of Yb3+ ion concentration,the binding energy value of each element in the crystal changed slightly.Compared with the similar compounds,such as RbTiOPO4,Yb2TiO3 and Yb2O3,langbeinite-type Rb2Ti2-xYbx(PO4)3 crystal materials have stronger Ti-O ionicity,weaker Yb-O ionicity and weaker P-O covalency.The crystal composition and group vibration mode were characterized by IR spectroscopy and Raman spectroscopy,and the results were consistent with the typical characteristics of the reported langbeinite phosphate crystals.Ultraviolet-visible diffuse reflectance spectroscopy shows that the three groups of crystals all have two obvious absorption peaks at 910 and 972 nm,corresponding to the Yb3+ion electron transfer from the ground state 2F7/2(0)to the excited state 2F5/2(2 ')and 2F5/2(1').The band gap value of Rb2Ti2-xYbx(PO4)3 crystal increases with the increase of Yb3+ ion doping coVcentration.Rb2Ti2-xYbx(PO4)3 crystal has strong blue and red dual-band up-conversion luminescence.With the increase of Yb3+ion doping concentration,the blue up-conversion luminescence peak gradually weakens.In terms of the red emission peak,there is little difference in the intensity of the langbeinite-type Rb2Ti2-xYbx(PO4)3 crystals with different doping concentrations.The blue emission peak conforms to the typical cooperative up-conversion luminescence characteristics,which originates from the simultaneous de-excitation of the Yb3+-Yb3+ion pair composed of two Yb3+ ions,while the red emission peak generation process is related to the defect zone in the crystal.The blue and red dual-band luminescence phenomenon of langbeinite-type phosphate shows that this type of crystal has potential application value in the field of up-conversion luminescence.(2)The langbeinite-type Rb2TiYb(PO4)3 microcrystalline material was successfully prepared for the first time by the high-temperature solid-phase reaction method,and experimental conditions such as suitable calcination temperature were explored.The difference between electronic structure and upconversion luminescence performance.The suitable calcination temperature for the preparation of pure phase Rb2TiYb(PO4)3 is 1000?.The microcrystals are characterized by SEM.The results show that the elements are uniformly distributed and the grain size is 10-20 ?m.At the same time,XPS was used to analyze the electronic structure of Rb2TiYb(PO4)3 microcrystalline materials at three temperatures,and it was found that compared with similar compounds,they have stronger Ti-O ionicity and weaker P-O covalency.The functional composition and group vibration mode were identified by infrared spectroscopy and Raman spectroscopy,and the vibration mode of the PO4 tetrahedral group was determined.Since the electrons in Yb3+transfer from the ground state 2F7/2 to the excited state 2F5/2,the UV-Vis spectra of such materials show absorption peaks at 910 and 972 nm,respectively,with a band gap value of 3.52 eV.Under the excitation of 980 nm laser,K2TiYb(PO4)3 produces strong blue light emission at 480 nm and weak red light emission at 654 nm.The CIE color coordinates of the samples at three different temperatures are all in the blue region,indicating that the material has potential application value in the field of blue up-conversion luminescence.(3)The K2TiYb(PO4)3 crystallites were successfully prepared for the first time by the high-temperature solid-phase reaction method,and the appropriate calcination temperature for the preparation of pure phase products was explored,which proves that the high-temperature solid-phase method can be used for different kinds of langbeinite phosphate crystals.The preparation shows the broad applicability of this method.The K2TiYb(PO4)3 microcrystals calcined at 1000? were characterized by SEM,and the grain size was 10-20 ?m.The electronic structure of K2TiYb(PO4)3 microcrystalline materials at three temperatures was characterized by XPS and it was found that compared with KTiOPO4,K2TiYb(PO4)3 microcrystals have stronger Ti-O ionicity and weaker P-O covalency.The identification results of IR spectroscopy and Raman spectroscopy on its functional composition and group vibration mode are consistent with the typical characteristics of langbeinite-type phosphate in the literature.The UV-Vis spectra of such materials show absorption peaks at 911 and 975 nm,respectively.Under the excitation of 980 nm laser,K2TiYb(PO4)3 produces stronger blue light emission at 480 nm and weaker red light emission at 653 nm.The mechanism of the two emission peaks in the photophysical process:the blue emission peak is produced by the synergistic effect of the Yb3+ion pair,and the red emission peak is related to the crystal defects inside the sample.After fitting the photoluminescence decay curve with a double exponential function,the lifetimes of the two are 268.6 ?s and 275.1 ?s,respectively.The CIE color coordinates of the samples at three different temperatures are in the blue region,indicating that the material has potential application prospects in the field of blue upconversion luminescence. |
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