Preparation Of Si-Na-Al-Zn Photo-thermal-refractive Glass And Study On Silver Clusters Induced Crystallization

Photo-thermal-refractive?PTR?glass has been used in volume gratings because of its refractive index modulation under ultraviolet radiation and heat treatment.At present,the main problem of fabricating grating elements based on PTR glass in the market is that the refractive index modulation degree of materials after heat treatment is generally low,and the low refractive index modulation degree and diffraction efficiency seriously limit the application prospects of PTR glass.NaF crystals induced by Ag⁰ clusters directly affect the refractive index modulation and diffraction efficiency.The size and number of Ag⁰ clusters are mainly determined by the properties of glass matrix,ultraviolet exposure and heat treatment.In this paper,Si-Na-Zn-Al system was chosen as PTR glass matrix,Ce³⁺and Ag⁺as photosensitive and thermal sensitive factors respectively.The precipitation of Ag⁰ clusters in boron-doped and alkali-rare earth photo-thermal-refractive glasses and their effects on the transmittance and crystallization of glasses were studied by optimizing the formulation,ultraviolet exposure dose and heat treatment conditions.The distribution of Na,F and Ag in volume bragg gratings was studied by characterizing the interference fringes of volume bragg gratings fabricated by PTR glass.The transformation of Ag⁰ clusters in PTR glasses and their induced NaF crystals were studied by means of transmission/absorption spectroscopy,fluorescence spectroscopy,TEM and SEM.The research main contents and results are as follows:1.On the basis of traditional PTR glass,a small amount of B₂O₃ was introduced to solve the problems of high melting temperature,high viscosity of glass liquid and difficult pouring of PTR glass.The physical,chemical and optical properties of boron-doped PTR glass were studied.Through the influence of different concentrations of Ce³⁺and Ag⁺on the optical properties of boron-doped PTR glass,such as transmission?absorption and color difference,the doping ratio of CeO₂ and AgNO₃ was finally determined to be 0.02 mo1%and 0.01 mol%are suitable.The influence of thermal fixing process?nucleation temperature T₁,nucleation time t₁,crystallization temperature T₂ and crystallization time t₂?on Ag⁰ cluster nucleation growth in boron-doped PTR glass is analyzed by orthogonal design method.Experiments show that when the UV exposure dose is 4 J/cm²@325 nm,the nucleation temperature T₁=490?and the crystallization temperature T₂=590?are suitable for boron-doped PTR glass,which can be obtained.The Ag⁰ clusters with suitable size also proved that the crystalline phase precipitated in the glass is NaF.2.In order to improve the refractive index modulation difference of PTR glass and solve the problem that B³⁺can inhibit the crystallization tendency,alkali rare earth PTR glass was prepared.By optimizing the UV exposure dose and heat treatment conditions,the changes of Ag⁰ clusters at various stages and their effects on the induction of NaF crystallization were studied.The results show that with the increase of UV exposure dose,Ag⁰ clusters grow rapidly,and the precipitation effect of NaF crystals will be affected.With the increase of nucleation temperature T₁,the size of[Ag⁰]₂,[Ag⁰]₃,[Ag⁰]₄ clusters gradually increases,resulting in red shift of the luminescence band at 400-600 nm and the decay of fluorescence lifetime.With the prolongation of crystallization heat treatment time,Ag⁰ clusters induce the precipitation of NaF.The transmittance of PTR glass increases and the color tends to be colorless when the NaF crystal is coated with Ag⁰ clusters.The uniform Ag⁰clusters and NaF crystals were obtained at the UV exposure dose of 4 J/cm²@315 nm,nucleation temperature of 580?and crystallization temperature of 650?.The structure and size of Ag⁰ clusters could be controlled by controlling the UV exposure dose and heat treatment parameters.3.In order to intuitively observe the writing of photothermal refractive glass and its volume grating,the PTR glass grating writing technology in Si-Na-Al-Zn system was studied.In order to better observe the writing of volume Bragg grating interference fringes,the etched volume Bragg grating was analyzed by line scanning.The experiment shows that the interference fringes in PTR glass are written by double-beam exposure method,and the silver clusters and NaF crystals are evenly distributed on the fringes with an interval of 3 microns.The research of silver clusters and NaF crystals in PTR and the fabrication of volume Bragg gratings are further discussed.