Material removal in the cutting process is regarded as a friction system with multiple input and output variables.The complexity of the cutting friction system is caused by the extreme conditions existing on the tool...Material removal in the cutting process is regarded as a friction system with multiple input and output variables.The complexity of the cutting friction system is caused by the extreme conditions existing on the tool–chip and tool–workpiece interfaces.The critical issue is significant to use knowledge of cutting friction behaviors to guide researchers and industrial manufacturing engineers in designing rational cutting processes to reduce tool wear and improve surface quality.This review focuses on the state of the art of research on friction behaviors in cutting procedures as well as future perspectives.First,the cutting friction phenomena under extreme conditions,such as high temperature,large strain/strain rates,sticking–sliding contact states,and diverse cutting conditions are analyzed.Second,the theoretical models of cutting friction behaviors and the application of simulation technology are discussed.Third,the factors that affect friction behaviors are analyzed,including material matching,cutting parameters,lubrication/cooling conditions,micro/nano surface textures,and tool coatings.Then,the consequences of the cutting friction phenomena,including tool wear patterns,tool life,chip formation,and the machined surface are analyzed.Finally,the research limitations and future work for cutting friction behaviors are discussed.This review contributes to the understanding of cutting friction behaviors and the development of high-quality cutting technology.展开更多
The most important consequence of adiabatic shear phenomenon is formation of sawtooth chip. Lots of scholars focused on the formation mechanism of sawtooth, and the research often depended on experimental approach. Fo...The most important consequence of adiabatic shear phenomenon is formation of sawtooth chip. Lots of scholars focused on the formation mechanism of sawtooth, and the research often depended on experimental approach. For the present, the mechanism of sawtooth chip formation still remains some ambiguous aspects. This study develops a combined numerical and experimental approach to get deeper understanding of sawtooth chip formation mechanism for Polycrystalline Cubic Boron Nitride（PCBN） tools orthogonal cutting hard steel GCr15. By adopting the Johnson-Cook material constitutive equations, the FEM simulation model established in this research effectively overcomes serious element distortions and cell singularity in high strain domain caused by large material deformation, and the adiabatic shear phenomenon is simulated successfully. Both the formation mechanism and process of sawtooth are simulated. Also, the change features regarding the cutting force as well as its effects on temperature are studied. More specifically, the contact of sawtooth formation frequency with cutting force fluctuation frequency is established. The cutting force and effect of cutting temperature on mechanism of adiabatic shear are investigated. Furthermore, the effects of the cutting condition on sawtooth chip formation are researched. The researching results show that cutting feed has the most important effect on sawtooth chip formation compared with cutting depth and speed. This research contributes a better understanding of mechanism, feature of chip formation in hard turning process, and supplies theoretical basis for the optimization of hard cutting process parameters.展开更多
Electropulsing is introduced into the cutting process for quenched and tempered 45 steel, which is a novel method to improve the material machinability compared with the conventional cutting process. The effects of el...Electropulsing is introduced into the cutting process for quenched and tempered 45 steel, which is a novel method to improve the material machinability compared with the conventional cutting process. The effects of electropulsing on cutting performances, microstructure evolution, and surface qualities of 45 steel rods were studied. The results indicate that electropulsing is beneficial for the cutting process in 3 aspects as follows：（1） reducing the principal cutting force, surface microhardness and surface roughness of the machined sample dramatically;（2） improving the machining efficiency and prolonging the life of cutting tools;（3） decreasing the thickness of rheological layer which was usually caused by work hardening in the cutting process. The morphology and microstructure of the cutting chips showed that the length of the chips increased significantly with the increase of the current density. The advantage of electropulsing is that it can improve the plastic deformation capability as well as increase the lubricating property between the specimen and the cutting tool.展开更多
This paper presents a constitutive framework for finite element analysis of the truck beam end cutting process.For this purpose,a finite strain anisotropic elasto-plastic model,which takes nonlinear kinematic and isot...This paper presents a constitutive framework for finite element analysis of the truck beam end cutting process.For this purpose,a finite strain anisotropic elasto-plastic model,which takes nonlinear kinematic and isotropic hardening into account,is presented.Three factors are investigated to determine the effect on cutting quality:radius of cutting tools,strength of materials and relative clearance in cutting.The recommendations made herein are based on the simulation results.展开更多
Thin-walled parts are typically difficult-to-cut components due to the complex dynamics in cutting process.The dynamics is variant for part during machining,but invariant for machine tool.The variation of the relative...Thin-walled parts are typically difficult-to-cut components due to the complex dynamics in cutting process.The dynamics is variant for part during machining,but invariant for machine tool.The variation of the relative dynamics results in the difference of cutting stage division and cutting parameter selection.This paper develops a novel method for whole cutting process optimization based on the relative varying dynamic characteristic of machining system.A new strategy to distinguish cutting stages depending on the dominated dynamics during machining process is proposed,and a thickness-dependent model to predict the dynamics of part is developed.Optimal cutting parameters change with stages,which can be divided by the critical thickness of part.Based on the dynamics comparison between machine tool and thickness-varying part,the critical thicknesses are predicted by an iterative algorithm.The proposed method is validated by the machining of three benchmarks.Good agreements have been obtained between prediction and experimental results in terms of stages identification,meanwhile,the optimized parameters perform well during the whole cutting process.展开更多
Experimentation data of perspex glass sheet cutting, using CO2 laser, with missing values were modelled with semi-supervised artificial neural networks. Factorial design of experiment was selected for the verification...Experimentation data of perspex glass sheet cutting, using CO2 laser, with missing values were modelled with semi-supervised artificial neural networks. Factorial design of experiment was selected for the verification of orthogonal array based model prediction. It shows improvement in modelling of edge quality and kerf width by applying semi-supervised learning algorithm, based on novel error assessment on simulations. The results are expected to depict better prediction on average by utilizing the systematic randomized techniques to initialize the neural network weights and increase the number of initialization. Missing values handling is difficult with statistical tools and supervised learning techniques; on the other hand, semi-supervised learning generates better results with the smallest datasets even with missing values.展开更多
By the use of ANSYS/LS-DYNA FEA software,numerical simulation on the cutting process of cutting plates with a reamer was carried out in the paper. The logical improvement was brought forward and the phenomenon of stre...By the use of ANSYS/LS-DYNA FEA software,numerical simulation on the cutting process of cutting plates with a reamer was carried out in the paper. The logical improvement was brought forward and the phenomenon of stress concentration was deceased by weighted analysis. The effects of different cut velocities and cutting thickness on life-spans of reamers were investigated, and the cutting parameters were optimized to satisfy the cutting precision and cutting efficiency. The study will provide a guide for the practical production.展开更多
The metal cutting process is accompanied by complex stress field,strain field,temperature field.The comprehensive effects of process parameters on chip morphology,cutting force,tool wear and residual stress are comple...The metal cutting process is accompanied by complex stress field,strain field,temperature field.The comprehensive effects of process parameters on chip morphology,cutting force,tool wear and residual stress are complex and inter-connected.Finite element method(FEM)is considered as an effective method to predict process variables and reveal microscopic physical phenomena in the cutting process.Therefore,the finite element(FE)simulation is used to research the conventional and micro scale cutting process,and the differences in the establishment of process variable FE simulation models are distinguished,thereby improving the accuracy of FE simulation.The reliability and effectiveness of FE simulation model largely depend on the accuracy of the simulation method,constitutive model,friction model,damage model in describing mesh element,the dynamic mechanical behavior of materials,the tool-chip-workpiece contact process and the chip formation mechanism.In this paper,the FE models of conventional and micro process variables are comprehensively and up-to-date reviewed for different materials and machining methods.The purpose is to establish a FE model that is more in line with the real cutting conditions,and to provide the possibility for optimizing the cutting process variables.The development direction of FE simulation of metal cutting process is discussed,which provides guidance for future cutting process modeling.展开更多
A thermodynamic model of hydrogen induced silicon surface layer splitting with the help of an oxidized silicon wafer bonded is proposed.Wafer splitting is the result of lateral growth of hydrogen blisters in the enti...A thermodynamic model of hydrogen induced silicon surface layer splitting with the help of an oxidized silicon wafer bonded is proposed.Wafer splitting is the result of lateral growth of hydrogen blisters in the entire implanted hydrogen region during annealing.The blister growth rate depends on the effective activation energies of both hydrogen complex dissociation and hydrogen diffusion.The hydrogen blister radius was studied as the function of annealing time,annealing temperature and implantation dose.The critical radius was obtained according to the Griffith energy condition.The time required for wafer splitting at the cut temperature was calculated in accordance with the growth of hydrogen blisters.展开更多
Cabbage harvester is very useful to replace the manual cabbage harvesting in China.The cutter with single-point clamping way can reduce the maximum and the average cutting force effectively,but may increase the splitt...Cabbage harvester is very useful to replace the manual cabbage harvesting in China.The cutter with single-point clamping way can reduce the maximum and the average cutting force effectively,but may increase the splitting failure.In this study,the mechanics model of cabbage root with single-point clamping way in cutting process was established.According to the analysis of mechanics model,when the sheer stress exceeded the sheer strength(τa>τ0),splitting failure began to occur.Meanwhile,if the maximum normal stress exceeded the tensile strength(σmax>σ0),the splitting failure would further become riving failure.The positions of splitting failure would almost locate at the cutting depth l equaled to R+r(l=R+r).To reduce the splitting failure,single factor and multi-factor cutting tests about the effect of sliding angle,cutting speed and cutting diameter on splitting failure were carried out.The results showed that the splitting failure would reduce with the increase of sliding angle,cutting speed and cutting diameter.Sliding angle,cutting speed,cutting diameter and the interactions of cutting speed with sliding angle and cutting diameter had significant effect on splitting failure level,and the interaction of sliding angle with cutting diameter and the 3 factors’interaction had no effect.To minimize splitting failure levels,the best cutting combination was that:sliding angle 40°,cutting speed 300 mm/min and cutting diameter 35 mm.This research can provide a basis of how to design a cutter for the cabbage harvester including the optimized cutting combination.展开更多
Based on the principle of Statistical Energy Analysis (SEA) for non-conservatively coupled systems under general excitations, relationship between noise radiated from and excitations on coupled complex structures is s...Based on the principle of Statistical Energy Analysis (SEA) for non-conservatively coupled systems under general excitations, relationship between noise radiated from and excitations on coupled complex structures is studied, which lays a foundation for the determination of noise/vibration energy by evaluation of exciting forces, and from that the quantitative analysis of the effects of an excitation on sound power from a sub-structure can be done. With extending of the relationship to the study of cutting noise, regression analysis method for evaluating the effects of cutting process on machine tool noise is established. Results show that cutting process has generally negligible effects on machine tool noise, and there is no apparent difference between machine tool noise in cutting condition and in idle one.展开更多
The N2O production in two nitrogen removal processes treating domestic wastewater was investigated in laboratory-scale aerobic-anoxic sequencing batch reactors （SBRs）. Results showed that N2O emission happened in th...The N2O production in two nitrogen removal processes treating domestic wastewater was investigated in laboratory-scale aerobic-anoxic sequencing batch reactors （SBRs）. Results showed that N2O emission happened in the aerobic phase rather than in the anoxic phase. During the aerobic phase, the nitrogen conversion to N2O gas was 27.7% and 36.8% of NH＋-N loss for conventional biologic N-removal process and short-cut biologic N-removal process. The dissolved N2O was reduced to N2 in the anoxic denitrification phase. The N2O production rate increased with the increasing of nitrite concentration and ceased when NH＋-N oxidation was terminated. Higher nitrite accumulation resulted in higher NEO emission in the short-cut nitrogen removal process. Pulse-wise addition of 20 mg NO2 -N. L- 1 gave rise to 3-fold of N2O emission in the conventional N-removal process, while little change happened with 20 mg NOS-N L-1 was added to SBR1.展开更多
In this work,calcium niobium gallium garnet(Ca_(3)Nb_(1.6875)Ga_(3.1875)O_(12)-CNGG)ceramic samples singledoped with Tb^(3+)and co-doped with Tb^(3+)and Yb^(3+)ions were sintered by the solid-state reaction method.The...In this work,calcium niobium gallium garnet(Ca_(3)Nb_(1.6875)Ga_(3.1875)O_(12)-CNGG)ceramic samples singledoped with Tb^(3+)and co-doped with Tb^(3+)and Yb^(3+)ions were sintered by the solid-state reaction method.The structural characterization of the samples was carried out by X-ray diffraction measurements.The optimal concentration of Tb^(3+)ions corresponding to the maximum luminescence in the green spectral range in CNGG:x at%Tb(x=0.1,0.5,1,2,3,4,and 5)was determined to be 4 at%.The timeresolved luminescence of the^(5)D_(4)level(Tb^(3+))in the CNGG:x at%Tb samples was analysed to explore the quenching mechanisms involved in the Tb^(3+)green emission.Co-doped CNGG:4 at%Tb,y at%Yb(y=0.5,2,4,6,8,and 10)ceramics were prepared and investigated.It is shown that CNGG:4 at%Tb,y at%Yb phosphors exhibit intense green luminescence under ultra-violet(UV),visible(VIS),and near-infrared(NIR)excitation,thus demonstrating the presence of simultaneous down-conversion(DC)and upconversion(UC)processes.The dependence of the UC luminescence intensity on the diode laser pumping power was measured and the results indicate a two-photon process based on cooperative energy transfer(CET).Under UV excitation,the lifetime of the^(5)D_(4)(Tb^(3+))level slowly increases with increase of Yb^(3+)concentration,suggesting the energy transfer from Yb^(3+)to Tb^(3+)ions,while under NIR excitation,the lifetime of the^(5)D_(4)(Tb^(3+))level decreases with increase of Yb^(3+)ions concentration,indicating the presence of a strong energy transfer from Tb^(3+)to Yb^(3+)ions.The highest energy transfer efficiency ofη_(ET)≈42%was determined for the CNGG:4 at%Tb,10 at%Yb sample.The obtained results indicate that CNGG:(Tb^(3+),Yb^(3+))could be efficient new yellowish-green-emitting phosphors.展开更多
基金financial support from the National Key Research and Development Program of China (2019YFB2005401)National Natural Science Foundation of China (Nos. 91860207 and 52175420)+5 种基金Shandong Provincial Key Research and Development Program (Major Scientific and Technological Innovation Project)(No. 2020CXGC010204)Shandong Provincial Natural Science Foundation of China (2021JMRH0301 and2021JMRH0304)Taishan Scholar FoundationInternational Partnership Scheme of the Bureau of the International Scientific Cooperation of the Chinese Academy of Sciences(No. 181722KYSB20180015)Research and Innovation Office of The Hong Kong Polytechnic University (BBX5and BBX7)funding support to the State Key Laboratories in Hong Kong
文摘Material removal in the cutting process is regarded as a friction system with multiple input and output variables.The complexity of the cutting friction system is caused by the extreme conditions existing on the tool–chip and tool–workpiece interfaces.The critical issue is significant to use knowledge of cutting friction behaviors to guide researchers and industrial manufacturing engineers in designing rational cutting processes to reduce tool wear and improve surface quality.This review focuses on the state of the art of research on friction behaviors in cutting procedures as well as future perspectives.First,the cutting friction phenomena under extreme conditions,such as high temperature,large strain/strain rates,sticking–sliding contact states,and diverse cutting conditions are analyzed.Second,the theoretical models of cutting friction behaviors and the application of simulation technology are discussed.Third,the factors that affect friction behaviors are analyzed,including material matching,cutting parameters,lubrication/cooling conditions,micro/nano surface textures,and tool coatings.Then,the consequences of the cutting friction phenomena,including tool wear patterns,tool life,chip formation,and the machined surface are analyzed.Finally,the research limitations and future work for cutting friction behaviors are discussed.This review contributes to the understanding of cutting friction behaviors and the development of high-quality cutting technology.
基金Supported by National Natural Science Foundation of China(Grant Nos.51105119,51235003)
文摘The most important consequence of adiabatic shear phenomenon is formation of sawtooth chip. Lots of scholars focused on the formation mechanism of sawtooth, and the research often depended on experimental approach. For the present, the mechanism of sawtooth chip formation still remains some ambiguous aspects. This study develops a combined numerical and experimental approach to get deeper understanding of sawtooth chip formation mechanism for Polycrystalline Cubic Boron Nitride（PCBN） tools orthogonal cutting hard steel GCr15. By adopting the Johnson-Cook material constitutive equations, the FEM simulation model established in this research effectively overcomes serious element distortions and cell singularity in high strain domain caused by large material deformation, and the adiabatic shear phenomenon is simulated successfully. Both the formation mechanism and process of sawtooth are simulated. Also, the change features regarding the cutting force as well as its effects on temperature are studied. More specifically, the contact of sawtooth formation frequency with cutting force fluctuation frequency is established. The cutting force and effect of cutting temperature on mechanism of adiabatic shear are investigated. Furthermore, the effects of the cutting condition on sawtooth chip formation are researched. The researching results show that cutting feed has the most important effect on sawtooth chip formation compared with cutting depth and speed. This research contributes a better understanding of mechanism, feature of chip formation in hard turning process, and supplies theoretical basis for the optimization of hard cutting process parameters.
基金Funded by National Natural Science Foundation of China(No.50571048)Research&Development Funding Project of Shenzhen(No.JCYJ20120619152539900)
文摘Electropulsing is introduced into the cutting process for quenched and tempered 45 steel, which is a novel method to improve the material machinability compared with the conventional cutting process. The effects of electropulsing on cutting performances, microstructure evolution, and surface qualities of 45 steel rods were studied. The results indicate that electropulsing is beneficial for the cutting process in 3 aspects as follows：（1） reducing the principal cutting force, surface microhardness and surface roughness of the machined sample dramatically;（2） improving the machining efficiency and prolonging the life of cutting tools;（3） decreasing the thickness of rheological layer which was usually caused by work hardening in the cutting process. The morphology and microstructure of the cutting chips showed that the length of the chips increased significantly with the increase of the current density. The advantage of electropulsing is that it can improve the plastic deformation capability as well as increase the lubricating property between the specimen and the cutting tool.
文摘This paper presents a constitutive framework for finite element analysis of the truck beam end cutting process.For this purpose,a finite strain anisotropic elasto-plastic model,which takes nonlinear kinematic and isotropic hardening into account,is presented.Three factors are investigated to determine the effect on cutting quality:radius of cutting tools,strength of materials and relative clearance in cutting.The recommendations made herein are based on the simulation results.
基金National Key R&D Program of China(Grant No.2018YFB1701901)Guangdong Provincial Key-Area Research and Development Program(Grant No.2020B090927002).
文摘Thin-walled parts are typically difficult-to-cut components due to the complex dynamics in cutting process.The dynamics is variant for part during machining,but invariant for machine tool.The variation of the relative dynamics results in the difference of cutting stage division and cutting parameter selection.This paper develops a novel method for whole cutting process optimization based on the relative varying dynamic characteristic of machining system.A new strategy to distinguish cutting stages depending on the dominated dynamics during machining process is proposed,and a thickness-dependent model to predict the dynamics of part is developed.Optimal cutting parameters change with stages,which can be divided by the critical thickness of part.Based on the dynamics comparison between machine tool and thickness-varying part,the critical thicknesses are predicted by an iterative algorithm.The proposed method is validated by the machining of three benchmarks.Good agreements have been obtained between prediction and experimental results in terms of stages identification,meanwhile,the optimized parameters perform well during the whole cutting process.
文摘Experimentation data of perspex glass sheet cutting, using CO2 laser, with missing values were modelled with semi-supervised artificial neural networks. Factorial design of experiment was selected for the verification of orthogonal array based model prediction. It shows improvement in modelling of edge quality and kerf width by applying semi-supervised learning algorithm, based on novel error assessment on simulations. The results are expected to depict better prediction on average by utilizing the systematic randomized techniques to initialize the neural network weights and increase the number of initialization. Missing values handling is difficult with statistical tools and supervised learning techniques; on the other hand, semi-supervised learning generates better results with the smallest datasets even with missing values.
文摘By the use of ANSYS/LS-DYNA FEA software,numerical simulation on the cutting process of cutting plates with a reamer was carried out in the paper. The logical improvement was brought forward and the phenomenon of stress concentration was deceased by weighted analysis. The effects of different cut velocities and cutting thickness on life-spans of reamers were investigated, and the cutting parameters were optimized to satisfy the cutting precision and cutting efficiency. The study will provide a guide for the practical production.
基金supported by the National Natural Science Foundation of China(No.52175393)。
文摘The metal cutting process is accompanied by complex stress field,strain field,temperature field.The comprehensive effects of process parameters on chip morphology,cutting force,tool wear and residual stress are complex and inter-connected.Finite element method(FEM)is considered as an effective method to predict process variables and reveal microscopic physical phenomena in the cutting process.Therefore,the finite element(FE)simulation is used to research the conventional and micro scale cutting process,and the differences in the establishment of process variable FE simulation models are distinguished,thereby improving the accuracy of FE simulation.The reliability and effectiveness of FE simulation model largely depend on the accuracy of the simulation method,constitutive model,friction model,damage model in describing mesh element,the dynamic mechanical behavior of materials,the tool-chip-workpiece contact process and the chip formation mechanism.In this paper,the FE models of conventional and micro process variables are comprehensively and up-to-date reviewed for different materials and machining methods.The purpose is to establish a FE model that is more in line with the real cutting conditions,and to provide the possibility for optimizing the cutting process variables.The development direction of FE simulation of metal cutting process is discussed,which provides guidance for future cutting process modeling.
文摘A thermodynamic model of hydrogen induced silicon surface layer splitting with the help of an oxidized silicon wafer bonded is proposed.Wafer splitting is the result of lateral growth of hydrogen blisters in the entire implanted hydrogen region during annealing.The blister growth rate depends on the effective activation energies of both hydrogen complex dissociation and hydrogen diffusion.The hydrogen blister radius was studied as the function of annealing time,annealing temperature and implantation dose.The critical radius was obtained according to the Griffith energy condition.The time required for wafer splitting at the cut temperature was calculated in accordance with the growth of hydrogen blisters.
基金The authors acknowledge the finical support of the National High Technology Research and Development Program of China through Project 2012AA10A504.
文摘Cabbage harvester is very useful to replace the manual cabbage harvesting in China.The cutter with single-point clamping way can reduce the maximum and the average cutting force effectively,but may increase the splitting failure.In this study,the mechanics model of cabbage root with single-point clamping way in cutting process was established.According to the analysis of mechanics model,when the sheer stress exceeded the sheer strength(τa>τ0),splitting failure began to occur.Meanwhile,if the maximum normal stress exceeded the tensile strength(σmax>σ0),the splitting failure would further become riving failure.The positions of splitting failure would almost locate at the cutting depth l equaled to R+r(l=R+r).To reduce the splitting failure,single factor and multi-factor cutting tests about the effect of sliding angle,cutting speed and cutting diameter on splitting failure were carried out.The results showed that the splitting failure would reduce with the increase of sliding angle,cutting speed and cutting diameter.Sliding angle,cutting speed,cutting diameter and the interactions of cutting speed with sliding angle and cutting diameter had significant effect on splitting failure level,and the interaction of sliding angle with cutting diameter and the 3 factors’interaction had no effect.To minimize splitting failure levels,the best cutting combination was that:sliding angle 40°,cutting speed 300 mm/min and cutting diameter 35 mm.This research can provide a basis of how to design a cutter for the cabbage harvester including the optimized cutting combination.
文摘Based on the principle of Statistical Energy Analysis (SEA) for non-conservatively coupled systems under general excitations, relationship between noise radiated from and excitations on coupled complex structures is studied, which lays a foundation for the determination of noise/vibration energy by evaluation of exciting forces, and from that the quantitative analysis of the effects of an excitation on sound power from a sub-structure can be done. With extending of the relationship to the study of cutting noise, regression analysis method for evaluating the effects of cutting process on machine tool noise is established. Results show that cutting process has generally negligible effects on machine tool noise, and there is no apparent difference between machine tool noise in cutting condition and in idle one.
基金This work was supported by the Science and Technology Research and Developmental Program of Hebei, China （No.12273611） and the National Natural Science Foundation of China （Grant No. 51008005）.
文摘The N2O production in two nitrogen removal processes treating domestic wastewater was investigated in laboratory-scale aerobic-anoxic sequencing batch reactors （SBRs）. Results showed that N2O emission happened in the aerobic phase rather than in the anoxic phase. During the aerobic phase, the nitrogen conversion to N2O gas was 27.7% and 36.8% of NH＋-N loss for conventional biologic N-removal process and short-cut biologic N-removal process. The dissolved N2O was reduced to N2 in the anoxic denitrification phase. The N2O production rate increased with the increasing of nitrite concentration and ceased when NH＋-N oxidation was terminated. Higher nitrite accumulation resulted in higher NEO emission in the short-cut nitrogen removal process. Pulse-wise addition of 20 mg NO2 -N. L- 1 gave rise to 3-fold of N2O emission in the conventional N-removal process, while little change happened with 20 mg NOS-N L-1 was added to SBR1.
基金Project supported by the Romanian Ministry of Research and Innovation under grant agreement no.16N/2019 within Program NUCLEULAPLASⅥ(PN-Ⅲ-P1-1.1-PD-2019-0665,PN-Ⅲ-P4-ID-PCE-2020-2203)。
文摘In this work,calcium niobium gallium garnet(Ca_(3)Nb_(1.6875)Ga_(3.1875)O_(12)-CNGG)ceramic samples singledoped with Tb^(3+)and co-doped with Tb^(3+)and Yb^(3+)ions were sintered by the solid-state reaction method.The structural characterization of the samples was carried out by X-ray diffraction measurements.The optimal concentration of Tb^(3+)ions corresponding to the maximum luminescence in the green spectral range in CNGG:x at%Tb(x=0.1,0.5,1,2,3,4,and 5)was determined to be 4 at%.The timeresolved luminescence of the^(5)D_(4)level(Tb^(3+))in the CNGG:x at%Tb samples was analysed to explore the quenching mechanisms involved in the Tb^(3+)green emission.Co-doped CNGG:4 at%Tb,y at%Yb(y=0.5,2,4,6,8,and 10)ceramics were prepared and investigated.It is shown that CNGG:4 at%Tb,y at%Yb phosphors exhibit intense green luminescence under ultra-violet(UV),visible(VIS),and near-infrared(NIR)excitation,thus demonstrating the presence of simultaneous down-conversion(DC)and upconversion(UC)processes.The dependence of the UC luminescence intensity on the diode laser pumping power was measured and the results indicate a two-photon process based on cooperative energy transfer(CET).Under UV excitation,the lifetime of the^(5)D_(4)(Tb^(3+))level slowly increases with increase of Yb^(3+)concentration,suggesting the energy transfer from Yb^(3+)to Tb^(3+)ions,while under NIR excitation,the lifetime of the^(5)D_(4)(Tb^(3+))level decreases with increase of Yb^(3+)ions concentration,indicating the presence of a strong energy transfer from Tb^(3+)to Yb^(3+)ions.The highest energy transfer efficiency ofη_(ET)≈42%was determined for the CNGG:4 at%Tb,10 at%Yb sample.The obtained results indicate that CNGG:(Tb^(3+),Yb^(3+))could be efficient new yellowish-green-emitting phosphors.
