Study Of Rare Earth Ion Probes In SiO₂-PbF₂ Glass-ceramics

Glass-ceramic materials have been widely used in color tunable displays,broadband optical amplifiers,bidirectional all-optical switches,mid-infrared fiber lasers,multimode temperature sensing and other fields.Luminescent materials doped with rare earth ions have potential applications in solar cells,fluorescent probes and other fields.Rare earth elements are very popular in the optical field because of their special properties and rich energy levels,so glass ceramics doped with rare earth elements have better mechanical properties,optical properties and insulation properties.The macroscopic properties and applications of glass-ceramics have been popularized,but the micro-environment of rare earth elements in glass-ceramics has been rarely studied by researchers.Luminescence of rare earth ions is closely related to crystal field,the electric dipole transition between the 4f energy levels of the rare earth ion causes other parity energy levels to be mixed into the 4f energy level under the action of the crystal field,and the probability of electric dipole transition affecting the 4f energy level of the rare earth trivalent ion is calculated by the J-O parameter calculated by J-O theory.In this paper,Er³⁺,Yb³⁺,Ho³⁺and SiO₂-PbF₂ doped glass and glass-ceramics samples with good transparency were prepared by high temperature solid state method.In addition,the samples were tested by differential thermal analysis（DSC）,X-ray diffraction（XRD）,absorption spectrum（ABS）and fluorescence spectrum（PL）,and a systematic study was conducted.The process of rare earth ions in glassy state entering the formed crystal during crystal growth is discussed in detail.the main contents are as follows:First,glass and glass-ceramic samples with SiO₂-PbF₂ matrix were prepared.The glass-ceramics are formed by glass heat treatment,and the influence of different heat treatment time on the micro-environment of rare earth ions entering the glass-ceramics was studied.It was found that Ho³⁺existed in the mixed phase of glass matrix and PbF₂crystal in the glass sample without heat treatment.However,Ho³⁺in the heat-treated glass matrix enters into the PbF₂ microcrystals,according to the qualitative analysis of absorption spectrum combined with J-O theory,with the increase of heat treatment time,the proportion of rare earth ions in the microcrystalline is larger.Different rare earth ions are replaced under the above matrix,and the proportion of Er³⁺entering the glass ceramic is calculated quantitatively by using J-O theory and absorption spectrum in the process of heat treatment by using Er³⁺as a probe.On the other hand,Er³⁺was used as a probe to investigate and analyze the changes of the glass-ceramic phase by combining with the fluorescence spectrum,the absorption spectrum and the XRD.The results show that most of the rare earth ions are still present in the glass phase,although the XRD pattern shows that PbF₂ crystals have been deposited in the precursor sample.And with the heat treatment time gradually increasing,the rare earth ions in the glass phase gradually enter the fluoride nanocrystals.At the same time,it is believed that rare earth ions can not only be used as nucleating agent to promote fluoride crystallization during heat treatment,but also be incorporated into nanocrystals during crystal growth.This process reflects the probe characteristics of rare earth ions,and understands the spectral characteristics of Er³⁺doped glass ceramics based on J-O theory,which can be used to study the application of temperature measurement.Under the excitation of 980 nm wavelength,the 520 and 545 nm green upconversion emission spectra of erbium-doped glass-ceramics were measured in a certain temperature range for the ratio temperature measurement based on fluorescence intensity ratio（FIR）.The sample has strong emission intensity,high-efficiency temperature measurement performance and thermally stable emission spectrum structure,and is a promising temperature measurement luminescent material.Compared with the commonly used ratio thermometer based on integral emission intensity,the multi-ratio thermometer is proposed and proved.