Research On Glass-forming Ability Of Aluminate Glasses And Luminescent Modulation Of Doped Chromium

Aluminate glasses exhibit an infrared?IR?absorption cutoff at wavelengths beyond 6?m while silicate?based glasses exhibit optical transmission at wavelengths less than 4.5?m.And the Young's Moduli of aluminate glasses reaches 112GPa which is superior to that of silica glasses.The excellent mechanical and optical properties make aluminate glasses candidate to be developed as fiber laser materials.However,its glass forming region is narrow and glass forming ability is poor,which poses great obstacle for developing aluminate glass fiber laser.To push aluminate glass one more step toward fiber laser,we have done the following research.1.To overcome difficulties on preparing aluminate glasses,we have optimized the aluminate glass forming ability in terms of compositions and preparation process.Glass network modifiers and formers have been introduced to promote the glass forming ability.For the glass network modifiers,the Na₂O and K₂O among monovalent metal oxide could suppress crystals forming in aluminate glasses and improve the glass forming ability.The thermal stability has been increased from 88 to 155 and 165?under 7mol%Na₂O and K₂O addition,respectively.Among divalent metal oxides,Mg O,Sr O and Ba O is beneficial to the glass forming ability,of which Mg O and Sr O are the more obvious.10mol%Sr O or Mg O addition has increased the thermal stability to 173 and 163?respectively and expand the glass forming area from 66-61mol%Ca O to 66-29mol%Ca O.Among trivalent metal oxides,the addition of Yb₂O₃,Er₂O₃,Ho₂O₃ could improve the glass forming ability,3mol%of which could significantly increase the thermal stability to above 156?.Yet,the addition of high-valent metal oxides is harmful to the formation of aluminate glass.For the glass network formers,the addition of trivalent oxide B₂O₃ could expand the glass forming region to 66-31mol%Ca O,and the thermal stability could be increased to 112?under 10 mol%B₂O₃ addition.The addition of tetravalent oxides Si O₂ and Ge O₂ would further expand the glass forming region to66-25mol%Ca O,and the addition of 10mol%Si O₂ and Ge O₂ could increase the thermal stability of aluminate glasses to 158 and 139?,respectively.The process conditions have been also optimized to solve the complete crystallization of big-bulk aluminate glasses.And the transparent and non-crystallized bulk aluminate glass was successfully prepared with melting temperature at 1550?,stirring time of 60 min,clarification time of 30 min and clarification time of 50 min.2.To prepare aluminate glasses with specific properties,we have analyzed the influence of the components on the performance of aluminate glasses.As for the mechanical properties:The introduction of glass network modifier would polymerize glass network to increase?decrease?the bond energy and decrease?increase?packing density of aluminate glass with the Al O₄ groups maintained,which increase glass hardness and stiffness.The introduction of Mg O polymerizes glass network,which increase the hardness and stiffness.The influence of Sr O and Ba O is opposite to that of Mg O.Yet,the addition of network formers?Si O₂,Ge O₂,B₂O₃?could destroy the Al O₄ framework and introduce new framework.These effects,together,lead to the decrease of the hardness and stiffness of aluminate glasses.As for the infrared transmittance:The infrared cut-off wavelength of aluminate glass with glass network modifiers introduced could still reach up to?6.4?m.Among glass network formers,the addition of B₂O₃ and Si O₂ would lead to the strong vibration absorption of B-O bond at?3.8 and 4.6?m and Si-O bond at?5.0?m respectively,which would greatly decrease the infrared transmittance of the aluminate glasses.Yet,the addition of the network former Ge O₂ would not harm the infrared transmittance of the aluminate glasses obviously,and the infrared cut-off wavelength of glass could still reach?6.0?m when Ge O₂ introduced.3.To develop materials for tunable lasers,we have prepared chromium-doped aluminate glasses with high-efficiency broadband emission.To achieve broadband emission,we have doped chromium ions of rich energy levels in aluminate glass.Broadband emissions of Cr³⁺in the range of 650-950nm and Cr⁴⁺in the range of 1000-1500nm have been realized.The emission efficiency of spectral range of 1000-1500nm of Cr⁴⁺for tunable lasers has been improved.The chromium ions have been transformed into luminescent Cr⁴⁺ions by regulating the superoxide ions inside aluminate glasses,by which the luminescent intensity of Cr⁴⁺was enhanced by 15 times.In addition,the addition of Sr O resulted in the crystal field modulation around Cr³⁺,which induces the appearance of a new Cr³⁺luminescent center at 708 nm and further broadens the emission range of Cr³⁺in aluminate glasses.