| Functional crystal materials have been widely used in many fields such as electronic information,aerospace,artificial intelligence,biomedical,energy storage and so forth.However,with the rapid development of science technology and society,existing functional crystal materials cannot meet the requirements of higher service environment.Therefore,it is of great practical significance to explore novel crystal materials.Among various inorganic functional crystal materials systems,phosphate crystals have always been attracted much attention due to their good properties such as rich structural types,wide transmission range,good physical and chemical properties and etc,where the number of phosphate crystals are up to thousand.In order to explore novel phosphate crystal materials,the phosphate crystals of the eulytite structure are selected as the research object in this thesis.The research of ReM3(PO4)3(Re:La,Nd,Gd,Y and Yb;M=Sr and Ba)and rare-earth ions(Nd3+,Yb3+,Tm3+and Er3+)doped crystals are systematically carried out.The single crystal growth,mechanical,thermal,laser and piezoelectric properties of these crystals were systematically investigated and studied to explore the potential application in the fields of the ultra-short pulse laser and piezoelectric acoustic devices.The main research contents and conclusions are as follows:(1)Growth and basis properties of the ReM3(PO4)3 crystalsReM3(PO4)3(Re=La,Nd,Gd,Y and Yb;M=Sr and Ba)and rare-earth ions(Nd3+,Yb3+,Tm3+and Er3+)doped crystals with a dimension of centimeter and good quality are grown using the Czozhralski method by the component design,temperature field control and growth parameters optimization,where the key technological parameters for growing high quality single crystal are obtained.The structures of YSr3(PO4)3,GdSr3(PO4)3,LaBa3(PO4)3,NdBa3(PO4)3,GdBa3(PO4)3,YBa3(PO4)3 and YbBa3(PO4)3 crystals are determined using the single crystal X-ray diffraction method.Results show that as-grown crystals belong to the cubic system with a point group of 43m.Crystal structures are composed of isolated PO4 tetrahedron and edge-shared Re/MO6 octahedron,where the disordered structure is due to the cations of Re3+ and M2+are randomly distributed in the same lattice with a ratio of 1:3.The basis properties of the ReM3(PO4)3 crystals are systematically investigated,including hardness,density,thermal properties(specific heat,thermal expansion,thermal diffusion and thermal conductivity)and optical properties(UV-visible spectra,transmittance spectra,refractive index and laser damage threshold),which lay a good foundation for the design and development of photoelectric devices.(2)Spectra and laser properties of the rare-earth ions doped ReM3(PO4)3 crystalsThe absorption spectra,fluorescence spectra and continuous-wave laser operation of the 0.5 mol%Nd3+-doped YBa3(PO4)3,YSr3(PO4)3 and GdSr3(PO4)3 crystals are systematically investigated at room temperature.Results show that these crystals possess a wide absorption spectra(～21 nm@804 nm)and emission spectra(～22 nm@1060 nm),which is much larger than that of the traditional laser crystals and comparable to the neodymium glass.Thus,these crystals possess a good application prospect in the field of tunable and ultra-fast laser.In addition,the corresponding spectra parameters of these crystals are calculated using the theory of Judd-Ofelt and the continuous-wave laser oscillation are firstly realized at the region of 1μm.The absorption spectra,fluorescence spectra and continuous-wave laser operation of the 6 mol%Yb3+-doped YSr3(PO4)3(Yb:YSP)crystal are systematically investigated at room temperature.Results show that the maximum absorption peak of Yb:YSP crystal is lied in 976 nm and the corresponding absorption cross section is found to be order of 1.31×10-20 cm2.Furthermore,Yb:YSP crystal possesses a wide emission spectra and fluorescence lifetime with values of 55 nm(@1013 nm)and 1267 μs,respectively,which indicates that this crystal has a good application prospect in the field of ultrashort pulse and Q-switched laser.In addition,Yb:YSP crystal can achieve dual-wavelength laser output(Δυ=2.2 THz),which can be applied to the terahertz light source.The absorption spectra and fluorescence spectra of the 5 mol%Tm3+-doped YSr3(PO4)3(Tm:YSP)crystal are systematically investigated and analyzed at room temperature.Results indicate that the Tm:YSP crystal possesses relatively strong absorption peak with an absorption full width at half-maximum of～21 nm at 792 nm,which can be well matched with the wavelength of commercial pump source of laser diode and is beneficial for the improvement of the pump efficiency.Furthermore,the full width at half-maximum of emission spectrum is determined to be～201 nm,corresponding to a central wavelength of～1800 nm.All results show that Tm:YSP crystal is a promising laser host in the field of ultra-short pulse and tunable laser with a region of 2 μm.The absorption spectra and emission spectra of the 30 mol%Er3+-doped YSr3(PO4)3(Er:YSP)crystal are investigated at room temperature.Results indicate that the Er:YSP crystal possesses relatively strong absorption peak with an absorption full width at half-maximum of～18 nm at 974 nm,wich can be well matched with the wavelength of commercial InGaAs LD pump source with a center wavelength of 976 nm and is beneficial to the absorption of pump light.Furthermore,Er:YSP crystal possesses a wide emission spectrum bandwidth with a value of 140 nm in the range of 2600 to 3500 nm,which is beneficial for the generation of ultra-short pulse laser.(3)Characterizations of the piezoelectric property for the ReM3(PO4)3 crystalsThe full set of electro-elastic constants of the ReM3(PO4)3(Re:La,Nd,Gd,Y and Yb;M=Sr and Ba)crystals are determined by using the resonance method,LCR bridge and ultrasonic methods.Furthermore,the temperature dependence for the ReBa3(PO4)3 crystals are investigated over the temperature of 25 to 800℃.Results indicate that the electro-elastic constants of these crystals possess good temperature stability,which is promising crystals in the field of high temperature piezoelectric.The relationship between structure and property of ReBa3(PO4)3(Re:La,Nd,Gd,Y and Yb)crystals are investigated and studied.Result shows that the dielectric and piezoelectric properties of these crystals are mainly related to the polyhedral distortion and dipole moment,which provides a novel idea for the development of piezoelectric crystals with excellent performances.(4)Analysis of the piezoelectric vibration mode and design of devicesThe face shear vibration mode d36 of the YSr3(PO4)3 crystal is analyzed using the finite element simulation and the optimal crystal cut with high piezoelectric coefficient and pure vibration mode is designed,i.e.Z/0°.Based on the optimal crystal cut,the prototype device of horizontal shear wave(SH0)piezoelectric transducer is designed using the piezoelectric mode d36.The finite element simulation and experimental results show that designed transducer can excite single-mode SH0 wave in four main directions(0°,90°,180°,270°)with a wide frequency range(300～500 kHz in this paper)and can be also used as a sensor to detect SH0 wave,indicating that the potentials of these crystals for high temperature structure health monitoring and nondestructive testing applications.Taking the high temperature piezoelectric acceleration sensor as the design object,the longitudinal stretching vibration mode d33 and thickness shear vibration mode d26 of the YSr3(PO4)3 crystal are analyzed and the optimal crystal cut with high piezoelectric coefficient and relatively pure vibration mode is designed,i.e.(ZXtl)45°/55° and(YXl)/45°,respectively.Furthermore,the prototype devices of the compression and shear high temperature acceleration sensors are designed based on the optimal crystal cut.Experiment results show that the relatively stable signal is obtained in the temperature range of 25 to 650℃,where the variation of sensitivity is less than 10%.A potential application of the ReM3(PO4)3 crystals in piezoelectric sensor field is developed. |
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