Preparation And Upconversion Properties Study Of Rare Earth Doped Germanate Glasses And Glass Ceramics

Efficient rare earth upconversion luminescence benefits from the low phonon energy of the host material and a high concentration of rare earth ion doping or enrichment while avoiding concentration quenching.The low phonon energy and high rare earth ion solubility properties of germanate glasses make them a class of host materials well suited for rare earth luminescence.In this paper,two germanate glasses,Ge O₂-Al₂O₃-Ca F₂-Na F-Yb F₃-Tm F₃（GACN）and Ge O₂-Al₂O₃-Na F-YF₃-Yb F₃-Tm F₃-Er F₃（GANY）,were designed and prepared.Subsequently,two germanate transparent glass ceramics embedded with metal-rare earth fluoride type crystals were obtained for the first time by heat treatment,and the properties were systematically investigated before and after glass crystallisation.The research details are described below:（1）The GACN glass was prepared by melt quenching method.According to the DSC curves,a two-stage sequential heat treatment scheme was developed to produce highly transparent glass ceramics.The first precipitation of metal-rare earth fluoride type crystals in a germanate glass with only Ge O₂as the glass-forming body has been demonstrated by XRD,TEM and FE-SEM,with the crystalline phase Ca₂Yb F₇and a size of about 30 nm.Glass ceramics maintained a high transmittance of approximately71%at 500 nm.Under the excitation of 980 nm,the upconversion emissions of glass ceramics were greatly enhanced,especially the emission of ³F_2,3energy level of Tm³⁺ion.Finally,temperature sensing based on the Tm³⁺ion indirect thermally coupled energy level was developed using the FIR technique.Within 323～573 K,maximum relative sensitivities of 1.85%K^-1and 1.37%K^-1,maximum absolute sensitivities of8.56×10^-2K^-1and 16.01×10^-2K^-1,optimum resolutions of±0.79 K and±0.62 K and optimum repeatabilities of 97.6%and 99.2%were obtained in glass and glass ceramic respectively.These demonstrate that glass and glass ceramics were not only suitable materials for upconversion luminescence,but also have excellent potential for applications in FIR optical temperature sensing.（2）The GANY glass was prepared by melt quenching method and transparent glass ceramics were obtained by one-step heat treatment method.XRD,FE-SEM and TEM showed that a large number of spherical Na Y₃F₁₀crystals,approximately 27 nm in size,were uniformly distributed in the residual glass host.The Ba F₂was introduced into glass ceramic as an internal standard and the crystallinities of glass ceramics were quantitatively analyzed using the Rietveld method,and it was found that the amount of Na Y₃F₁₀in them were close to the theoretical upper limit.The luminescence intensity of the glass ceramics reached approximately 400%of that of glass under the 980 nm excitation.Then a new continuous high sensitivity luminescence thermometry was constructed based on the multi-colour emissions of Tm³⁺and Er³⁺ions.Within 323～573 K,relative sensitivity was maintained at continuously high level(1.30～2.61%K^-1).And high resolution of±0.13 K and a high reproducibility of 99.6%were also achieved.Clearly,this glass ceramic has great potential for rare earth upconversion luminescence and optical temperature sensing.The proposed multi-scheme FIR combination strategy is feasible and effective for thermometry performance enhancement.The above results provide powerful references for the research and development of new germanate transparent glass ceramics embedded with rare earth fluoride nanocrystals suitable for rare earth luminescence.In addition,two ideas to improve the FIR thermometry performance are presented,one is the application of indirect thermally coupled energy levels of Tm³⁺ions and the other is the multi-scheme FIR combination strategy.