Structure and Optical Properties of Silicate Glass-ceramics Doped with Valence-variable Ions

Author:Chen Jie Jie

Supervisor:zhou shi feng

Database:Doctor

Degree Year:2019

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Pages:142

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With the rapid development of information technology,photonic glass and fiber play a crucial role in the optoelectronic information industry,such as large-capacity information transmission,high-precision laser processing and high-precision flat touch display.As an important type of photonic glass,photonic glass-ceramic combines the advantages of crystals and glass.For example,it possesses unique properties including enhanced radiative transition probablity,high doping concentration,and easy fabrication.In addition,it also owns the advantages of high mechanical and chemical stability,high resistance to laser and thermal damage threshold.Therefore,it is of great significance to study the structure and optical properties of photonic glass-ceramic,which can provide design criteria and theoretical support for the development of nanostructured materials.This thesis provides a comprehensive review of the crystallization theory and classification of transparent glass-ceramics,gives an overview of several applications for photonic.As we know,valence-variable ions are difficult to be activated in amorphous glass structure.To overcome this limitation,the typical valence-variable ions such as transition-mental and rare-earth ions(e.g.Cr,Fe and Eu)were chosen as the optical centers.Based on crystal-field theory and selective doping mechanism,we expected the selective activation of valence-variable ions in multiple lattice sites.Several new types of photonic glass-ceramics have been developed and prepared successfully.Differential Scanning Calorimeter(DSC),X-ray diffraction(XRD),high-resolution transmission electron microscopy(HRTEM),X-ray absorption spectroscopy,transmission/absorption spectra,photoluminescence spectroscopy were used to study the structure and optical properties.Several types of transparent glass-ceramics with unique optical properties were obtained,including optical temperature sensing,ultra-broadband near-infrared(NIR)luminescence,multicolor luminescence and nonlinear optical properties.Two types of transparent Cr-doped B2O3-Al2O3-SiO2 glass-ceramics containing Al6Si2O13nanocrystals and dual nanocrystals(Al6Si2O13 and Ga2O3)were prepared successfully.Base on the mechanism of selective doping,Cr3+is more likely to enter into the octahedral coordination environment of Ga2O3 nanocrystals.We suppose that the strong preference of active center for special coordination,octahedral position for Cr3+here,might be the underling driving forces for doping.It is interesting that 0.2 mol%Cr3+ions inhibit the precipitation of Al6Si2O13nanocrystals and promote the precipitation of Ga2O3 nanocrystals.The values of crystal-field strength Dq/B for Cr3+-doped glasses and glass-ceramics were adjustable from 2.17 to 2.74.Another interesting point observed in Cr3+-doped glass-ceramic containing dual nanocrystals is that the luminescence intensity increases with the enhancement of ambient temperature.It is supposed that the trap centers in Ga2O3 semiconductor can be excited at high temperature,and then the energy transfer occurs between Ga2O3 and Cr3+.The optical temperature sensing performance of the paired thermal coupling levels of 2E and 4T2 was characterized by fluorescence intensity ratio(FIR)technique.The results show that the relative sensitivity SR reaches a maximum of 1.60%K-1 at 423 K.Transparent Cr-doped MgO-Al2O3-SiO2 glass-ceramic containing Mg2SiO4 nanocrystals was prepared successfully and characterized.Replacing the K2CO3 by using KNO3 in glass composition does not change the structure of glass-ceramic,but it can greatly promote the oxidation from Cr3+to Cr4+and increase the content of Cr4+ions.As a result,the glass-ceramic shows interesting luminescent characteristics with four emission bands originated from high crystal field Cr3+and Cr4+ions respectively.The overlapping of these emission bands leads to the ultra-broadband NIR luminescence with the large full width at half maximum(FWHM)of about 340 nm.The Z-scan optical setup was employed for measurement of the nonlinear absorption of glass-ceramic.The fitted values ofσgs andσes were 1.39×10-16 and 1.20×10-16cm2,respectively.Notably,this is the first trial,to the best of our knowledge,to use Cr4+-doped glass-ceramic as a saturable absorber,and the passive Q-switched pulse generation of Nd3+ions at 1064 nm was realized.The repetition frequency was 250 kHz and the pulse width was 176ns.Glass-ceramic fiber with core-clad configuration was successfully prepared by melt-in-tube method.Highly transparent BaO-Al2O3-SiO2 glass-ceramic,in which,most of LaF3 nanocrystals assembled in micro-sized BaAl2Si2O8 single crystals was prepared successfully and characterized.The multiscale structure can induce efficient multiple scattering and generate optimal optical modes to confine light inside the matrix.Because Eu3+and Eu2+ions selectively occupy the octahedral positons of LaF3 and BaAl2Si2O8 crystals,a significant decrease in the energy-transfer rate can be realized and it ensures an efficient emission output.Multiscale structured glass-ceramic presents unique bright and tunable multi-color luminescence,including blue,red and even white,simply by switching the excitation wavelength from 324,393 to 376 nm.In addition,the multi-color luminescence can also be tuned by changing the ambient temperature.The effects of low doping concentration(less than 2.0 mol%)of Fe on the crystallization behavior and intrinsic optical properties of K2O-Al2O3-SiO2 glass-ceramics embedded with ZnO were investigated.The non-isothermal crystallization kinetics of glass was characterized by the modified JMA formula.The results show that the doping concentration affects the crystallization behavior of the glasses,and the greatest tendency is observed in the samples doped with 0.6 mol%Fe.The strong infrared localized surface plasmon resonance(LSPR)absorption in glass-ceramic can be attributed to the increase in carrier concentration caused by Fe3+ions doping in ZnO.With the increase of the concentration of Fe3+,the dopant may capture a large amount of free electrons,and the deep levels introduced by impurities and defects can also promote the recombination of electrons and holes.Above effects collaboratively result in a significant reduction in carrier concentration.In addition,the exchange coupling of s-d and p-d between the localized d electrons of Fe can be enhanced,resulting in a significant reduction in optical band gap.The carrier decay process,which can be characterized by transient absorption spectroscopy,consists of two parts:(1)fast decay process with the time constant of102 fs is originated from the electron-phonon interactions;(2)slow decay process with the time constant of ps magnitude is originated from the phonon-phonon interactions.Benefited from the broadband LSPR absorption feature,0.2 mol%Fe-doped glass-ceramic shows excellent infrared radiance and photo-thermal conversion efficiency.