Novel Functional Glasses Fabricated By Containerless Processing

Glasses with unusual compositions and characteristic structures,especially those without a traditional glass network former,have remarkable optical,thermal and mechanical properties,making them highly attractive as laser gain materials,optical memory material,special fiber material and other important applications.However,it’s difficult to fabricate these glasses via conventional melt-quenching method because of their low glass-forming ability,which is very obstructive in area of research and applications.Containerless processing allows for deep undercooling in melt of different inorganic and metallic materials,and therefore is useful for vitrifying materials in bulk form with low glass-forming ability.It has opened up new ideas in research and application.Besides,this process is free of contamination and avoids heterogeneous nucleation due to the absence of contact interface with crucible,which provides excellent conditions for the study of the essential problems and phenomena of glass.Based on this technique,the preparation,properties and applications of new functional glasses were studied.(1)Rare earth doped alkaline earth metal aluminate glassesWe studied the photoluminescence and structural characteristics of Eu2+ doped aluminate glasses.We choose alkaline earth metal aluminate crystal materials and glass materials with the same composition as the research objects,and the effects of different matrices(crystalline and amorphous)on the photoluminescence and structural characteristics of the materials were compared.Observing the control of valence state of Eu in barium aluminate glass and ceramics,we find that the composition and structural requirements(strict 3-dimensional closed crystal structure)must be met to achive the reduction of Eu3+→Eu2+ in oxidizing atmosphere.It is not suitable for glass to maintain Eu2+ in oxidizing atmosphere due to the exisitence of large amount of irregular arrangements in the glass network structure.We observed the long persistence of Eu2+ doped alkaline earth metal aluminate(CaAl2O4 and(CaSr)0.5Al2O4)crystalline and glass material.The characteristic luminescence of Eu2+ can be observed in both crystalline materials and glass materials while the long afterglow can only be observed in crystalline materials.We studied the mechanism of long persistence and discuss the absence of long persistence in alkaline earth metal aluminate glass.From the perspective of structure al,it can be concluded that the exisitence of large amount of defective energy levels results in the absence of long persistence phosphorescence in the glasses.(2)Erbium doped gallate and aluminate glassesWe prepared a series of transparent gallate and aluminate glasses(44CaO-56Al2O3,44CaO-28Ga2O3-28Al2O3,44CaO-56Ga2O3 with different Er doping concentrations.The glass forming ability and thermal stability are studied and the glass structures are is analyzed.Al and Ga elements are in a tetrahedral coordination environment in the glass network structure,and A1 and Ga play a role in network formation in the absence of traditional glass network former.The presence of Al will contribute to incerase the quenching concentration of the up-conversion fluorescence of Er,but also reduce the quenching concentration of NIR fluorescence.The introduction of Ga reduces the fluorescence life,which is due to the increase of the density and refractive index of the glass because of the large atomic weight of Ga,resulting in an increase in the radiation transition rate of Er ions.(3)N doped tantalum aluminate glassesWe prepared the nitrogen doped tantalum aluminate glass with the composition of 46Ta2O5-(54-x)Al2O3-x(2AlN),which is the first time to achieve the introduction of N in glass by containerless processing.N join into the glass structure by replacing O,and the formed Al-N bond is more covalent than Al-0 bond.Due to the three coordination characteristic of N(O is a binary coordinate),the cross-link of glass structures becomes tighter,so that the refractive index,density,hardness and elastic modulus of glass increase,while the glass forming ability decreases.(4)Bismuth doped silica glassesWe prepared bismuth doped silica glass with the composition of SiO2:Bi,98SiO2-2Al2O3:Bi and 96SiO2-2Al2O3-2GeO2:Bi,which is the first time to achieve the introduction of Bi in silica glass by containerless processing.The prepared glass has good glass forming ability and high concentration(5%)of Bi doping can be achieved.The higher the Bi doping concentration,the higher proportion of Bi0 is in the glass.In SiO2:Bi glass,the fluorescence quenching concentration is above 3%.The introduction of Al2O3 will increase the thermal conductivity of the raw materials,while the introduction of GeO2 can improve the fluorescence performance and reduce the glass melting point.Discussing the near infrared fluorescence mechanism of Bi doped glass,we speculate that the luminescence centers in SiO2:Bi glass are Bi+ and Bi0 while the centers in 98SiO2-2Al2O3:Bi and 96SiO2-2Al2O3-2GeO2:Bi glass are Bi+ions in different chemical environments.