Growth Of Re³⁺ Doped Fluoride Laser Crystal By Vertical Bridgman Technique

Rare earth ions doped fluoride crystals is an imprtant research project in the field of solid statelaser technology. Growth of large-size fluoride crystals with high quality is a necessary technicalcondition for the solid laser devices and their applications. So far many research institutes havebeen appllying the traditional Czochralski method as the main technique for preparing the fluoridelaser crystals, in which the fluoride crystals are normally grown in a sealed vaccum or CF4atmosphere. Re3+ions doped LiYF4crystals are a kind of fluoride laser materials acquired muchattention in the field of solid state laser technique. It has been verified that the laser output rangedfrom infra red to violet region can be acquired by means of the solid laser devices based on theRe3+: LiYF4crystal rods as the optical elements. The research work on the Bridgman growth ofseries of Re3+ions doped LiYF4crystals is reported in this thesis. This thesis presents thepreparation of Re3+: LiYF4polycrystalline materials, the growth of large-size crystal and thecharacterizations of spectral properties. The main researched results in this thesis are summarizedas follows:(1) The solid state synthesis of Re3+doped fluoride polycrystalline material. Using high purityLiF, YF3, YbF3, NdF3, PrF3as the initial materials, the charge material was prepared according tothe molar ratio of LiF: ReF3: YF3=51.5: x:(48.5-x). The charge material was synthesized intoRe3+doped LiYF4composite fluoride polycrystallites by means of solid state reaction at elevatedtemperature in the dried HF atmosphere. As-prepared white ingot has been verified as a kind ofdried solid solution polycrystalline material with Re3+ions doped into LiYF4crystal lattice. Thepolycrystalline material can be used in the growth of large-size crystal Re3+:LiYF4with desirabletransparency.(2) The Bridgman growth of Re3+doped fluoride single crystal LiYF4. Using the driedpolycrystalline material prepared by solid state reaction, a series of Re3+ions doped LiYF4crystalswere grown by vertical Bridgman method. The furnace temperature was controlled at930~940℃and the temperature gradient near solid-liqiud interface was adjusted at30~40℃/cm. By theBridgman growth under sealed non-vacuum atmosphere with the crucible lowering rate of0.6~0.8mm/h, a series of large-size Re3+: LiYF4crystals with deasirable transparency had been grownsuccessfully, including Yb3+: LiYF4, Nd3+: LiYF4and Pr3+: LiYF4crystals. (3) The materials chemistry investigations of Re3+doped fluoride single crystal LiYF4. Aseries of samples were fabricated from as-grown single crystals. The fluoride crystal samples werecharacterized with the crystalgrahphic phases, thermalchemical properties and Re3+ions dopantconcentration by X-ray diffraction, DTA/TG and ICP-AES analysis. It has been verified that Re3+ions can be doped into the matrix crystal LiYF4with moderate segregation coefficients. The othermaterial chemistry problems deals with the crystal growth were also discussed in the thesis.（4）The spectral properties of Re3+doped fluoride single crystal LiYF4. The spectralproperties of Re3+: LiYF4crystals were investigated based on the measurements of absorptionspectra, transmission spectra, fluorescence spectra and photoluminescence decay spectra. It showsthat Yb3+:LiYF4presents a strong absorption with a wide wavelenth range around960nm. Underthe photonic excitation at896nm, the single crystals possess a fluorescence emission at thewavelength ranges from930to1030nm with decay life time of1888μs. Nd3+: LiYF4singlecrystal exhibits a series of typical absorption peaks corresponding to Nd3+ions in the range from400nm to1200nm. The fluorescence emissions within930-1030nm wavelength range can beacquired upon the infra red photonic excitation. The typical absorption peaks corresponding to Pr3+ions in the range from300nm to800nm were also observed for Pr3+: LiYF4crystal.The Bridgman growth of optical frequency-douled crystal BaMgF4was also studied in thiswork. The polycrystalline material was synthesized by solid-state reaction at high temoerature andBaMgF4single crystal was grown by the modified Bridgman method. The transmittance spectrumfor the crystal sample show that the optical transmittance approaches82%between350nm and800nm with a transmittance limit located at220nm. It proves the fluoride single crystal to be apromising violet optical frequency-douled material for the laser applications.