Study On Preparation And Properties Of Sm²⁺ Doped Mg_0.27Al_2.58O_3.73N_0.27 Transparent Ceramics

Spinel-type transparent ceramic of Mg_0.27Al_2.58O_3.73N_0.27.27 is transparent-structure materials with excellent physicochemeical properties,while one of key research fields is the functionalization of it by doping activator ions.The rare earth Sm²⁺ions possess good luminous efficiency and spectral diversity,which make them be frequently-used activators in optical functionalized organic and inorganic materials.Through adding different amount of Sm₂O₃ into raw powder of Mg_0.27Al_2.58O_3.73N_0.27 transparent ceramic and pressureless sintering,the Mg_0.27Al_2.58O_3.73N_0.27:Sm²⁺ceramics were prepared,which showed a diverse microstructure after pre-sintering.After subsequent hot isostatic pressing?HIP?,the Mg_0.27Al_2.58O_3.73N_0.27:Sm²⁺transparent ceramics with outstanding in-line transmittance and fluorescent function were obtained.In this dissertation,it revealed that the Mg_0.27Al_2.58O_3.73N_0.27:Sm²⁺(Sm²⁺:0.005⁰.030 at%)transparent ceramics have single phase and dense structure,which also exhibit good mechanical properties,thermal conductivity and excellent optical transparency with?75%in the range of intermediate IR.Luminescence centers mapping and the spectra analysis performed by the SEM-CL technique,which proved that the luminescence center(Sm²⁺ions)were concentrated on the narrow and relax grain boundary of Mg_0.27Al_2.58O_3.73N_0.27:Sm²⁺transparent ceramics.Moreover,from the result of the as-sintering samples under different pre-sintering temperature,we speculated that the Sm₂O₃ may reduce the pre-sintering temperature and promote the densification process of fluorescence transparent ceramics by reacting with the matrix and producing a liquid wetting the grain boundary.Because the preparation of ceramics was carried out in the intense reducing atmosphere provided by graphite furnace at high temperature and low oxygen pressure,the Sm₂O₃ was reduced to Sm²⁺.The analysis of fluorescence spectra indicated that excitation spectra of Mg_0.27Al_2.58O_3.73N_0.27:Sm²⁺transparent ceramics cover the wavelength range from ultraviolet of 250 nm to orange light of 600 nm,and peaks of excitation spectra at 275nm,346 nm,450 nm,475 nm and 510 nm could be assigned to the 4f⁶?4f⁵5d¹transitions of Sm²⁺.Under the excitation of 346 nm at room temperature,the Sm²⁺only exhibited 4f?4f transitions within the inner orbital of 4f with the strongest emission band center at 687 nm,which was belong to the ⁵D₀?⁷F₀ transition.Additionally,in order to study the fluorescence intensity ratio for temperature sensing,we have explored the temperature-dependent spectra of Sm²⁺ions within the temperature range of 300⁶90 K.The results indicated that the 4f⁵5d¹ configuration energy levels and ⁵D₀energy level of Sm²⁺ions exhibited the strong thermally coupled effect and the Mg_0.27Al_2.58O_3.73N_0.27:0.010at%Sm²⁺transparent ceramics showed a maximum absolute sensitivity of 0.1444 K^-1 at 690 K for temperature sensing,which showed greater superiority over other fluorescent materials.Meanwhile,through in-depth analysis of factors influencing on the absolute sensitivity,we found that a large amplification factor of constant B and suitable effect energy gap?E?close to kBT?could benefit the optimal absolute sensitivity in desired temperature range.The measurement of the lifetime of ⁵D₀ energy level indicated that the lifetime of⁵D₀?⁷F₀ transition was about 1.2 ms with monitoring wavelength of 687 nm,and it showed some decline with the increasing concentration of Sm²⁺ions.Furthermore,the lifetime of ⁵D₀?⁷F₀ transition exhibited excellent function relation with temperature in 300⁴90 K.At 490 K,Mg_0.27Al_2.58O_3.73N_0.27:0.010at%Sm²⁺transparent ceramics showed a maximum relative sensitivity of 1.13%K^-1 and could be well applied in temperature sensing.Based on the above research results,being an excellent structural and functional integration fluorescent material,Mg_0.27Al_2.58O_3.73N_0.27:Sm²⁺transparent ceramics could be potentially applied in contactless and real-time temperature sensing with dual mode of fluorescence intensity ratio and fluorescence lifetime.