Fabrication Of Er:CaF₂ Transparent Ceramics And The Optical Properties Modulated

Compared to the traditional solid laser gain mediums,transparent ceramics present high doing level with ions and can be produced in large size advantages,so transparent ceramics becoming an important direction in the solid gain mediums area.So far,the transparent ceramic are mostly based on the oxide compounds,such as YAG and Y₂O₃.Compared to oxide ceramics,CaF₂ matrix present several excellent advantages,such as wider optical transparency range,higher transmittance and lower phonon energy,so the CaF₂ is an ideal transparent ceramic matrix material.Among the rare earth ions,erbium ions(Er³⁺)has rich energy level structure and with various emission channel,such as in visible range and near infrared?around 1.5?m?wavelength.Therefore,the research present here,transparent ceramics were fabricated based on CaF₂ matrix material doped with Er³⁺ions.Additionally,Yb³⁺and Y³⁺ions were also codoped into the Er:CaF₂ transparent ceramics to enhanced the emission intensity and modulate the spectra properties of Er³⁺ion.First,pure CaF₂ nanoparticles were synthesized by the chemical coprecipitation method,and the ceramic was fabricated by the hot pressed sintering in a vacuum environment.The results obtained in the TG-DSC analysis for the nanoparticles,indicating that the keeping mass lose during the whole treatment,and different peaks corresponding decompose of oxide groups.The optical transmission of CaF₂ ceramic sample reached 40%at 1500nm wavelength.As for the Er doped CaF_{2 c}eramic fabrication,Nanoparticles of Er:CaF₂ were synthesized by a chemical coprecipitation method.The results obtained by the X-ray diffraction and TEM analysis reveal that the Er:CaF₂ nanoparticles were single fluorite structure,the size and shape of the CaF₂ nanoparticles were modified by doping with Er³⁺.The nanoparticles size of the obtained Er:CaF₂ were less than 100nm,and the average nanoparticles size was decreased from about 30nm to 16nm with increasing Er concentrations from 1mol%to 10mol%,while the lattice constant of CaF₂ matrix was increased from 5.47?to 5.49?.Er:CaF₂ transparent ceramics were fabricated under vacuum environment and 30MPa pressure.The influence of Er³⁺ions doping concentrations and sintering temperatures on microstructure and the optical transmission of Er:CaF₂ transparent ceramics were investigated.With the increasing of Er³⁺doping concentration,the grain size of the transparent ceramics increasing firstly and then decreasing,and the transmission of the ceramic samples were also increasing firstly and then decreasing,the Er?5 mol?:CaF₂ transparent ceramic present the highest transmission.With temperatures increases from 750?to850?,the transmissivity of ceramic samples increases at 750?to 800?and then decreases at 800?to 850?,and the transmissivity of Er?5 mol%?:CaF₂ transparent ceramic sintered at 800?was 87%at 1200nm.The upconversion and near infrared?1.5?m?emission spectra of Er:CaF₂ ceramics were obtained under 980 nm excitation,and the upconversion emission spectra composed with two luminescence bands located at 550nm and 660nm.At low doping level,the green and red emission in upconversion spectra have nearly equal intensity.Strong cross-relaxation?CR?processes between Er³⁺ions occur at high Er³⁺doping level,and the red have a higher intensity than green emission.In order to improve the luminescence of Er ions in CaF₂ ceramics,Er,Yb:CaF₂nanoparticles were synthesized,and Er,Yb:CaF₂ ceramic samples were obtained by hot-pressed sintering method.The as-synthesized Er,Yb:CaF₂ nanoparticles were single fluorite phase with cubic structure,the particles size less than 100 nm.When Yb doping level increase to 5mol%,the average size of nanoparticles were about29.3nm?28.4nm?21.7nm and 18.7nm,respectively.The grain size of ceramic samples were also decreased with increasing Yb concentrations,while the optical transmission of ceramic samples were increased.After Yb codoping,the emission intensities of Er,Yb:CaF₂ ceramics were all enhanced,and the intensity ratios of the red to green luminescence R?r/g?decrease with the increasing Yb concentration.At high Er doping level,the Er:CaF₂ ceramics have a high optical transmission,while Er3+ions trend to formation clusters structure,and have a relatively low green emission.So,yttrium ions were selected as modulate ion,codoped into Er:CaF₂transparent ceramics.Er,Y:CaF₂ nanoparticles were synthesized and transparent ceramics were fabricated by hot-pressed sintering method.The particles size of as-synthesized Er,Yb:CaF₂ nanoparticles was less than 100 nm.With Y³⁺ions codoping,and size of Er,Y:CaF₂ was much smaller than the Er:CaF₂ nanoparticles,while the optical transmission was higher than single Er doped transparent ceramic,especially at visible range.The upconversion and infrared emission spectras of Er:CaF₂ and Er,Y:CaF₂ transparent ceramics under 980 nm excitation were observed.With Y³⁺ions codoping,the green emission intensity much stronger than the red emission band,the characterizations of infrared emission spectra was also modulated and the width of emission band was became norrow.