Preparation And Photoluminescence Characteristics Of Tb³⁺:Zn₂GeO₄ Nanophosphors And Tm³⁺/Tb³⁺/Eu³⁺ Bismuth Borosilicate Glass

Function materials doped rare earth?RE?ions are of a very wide range of applications in too many fields,such as superconductive material,permanent magnetic material,corrosion resistance and wear resistance film,and so on.They also have great application prospects especially in optics field,for examples,W-LED,laser,optical amplifier,etc.Therefore,the investigations on the optimization of preparing technology,analysis of luminescence mechanism about the materials doped RE have very important significance.The main works of this thesis include the following contents:Firstly,a series of Tb³⁺single-doped Zn₂Ge O₄ nanophosphors have been prepared by the high temperature solid state method and the optimized process parameters are given.At the same time,with the help of the XRD and SEM,the crystal structures and morphologies of the nanophosphors are characterized,respectively.And the results show that the diffraction peaks of the Zn₂Ge O₄ matrix material without doping any RE ions prepared in our experiment are consistent with those of the standard card.Compared with the standard card,the diffraction peaks of the Tb³⁺:Zn₂Ge O₄ phosphors are the same basically after being doped different concentration of Tb³⁺ions,however,a tiny blue shift phenomenon can be found and the maximum peak shift is 0.022?,meaning that there exists the weak influence of Tb³⁺dopant on the crystal structure of nanophosphor.The intrinsic reasons of the crystal structure change are discussed detailedly.It can be seen from the SEM photos that the synthesized Zn₂Ge O₄ host,Zn₂Ge O₄ doped 0.3 and 1.0 mol%Tb³⁺ions are all nanoparticles and the average sizes are about 50 nm,except the 0.7Tb³⁺:Zn₂Ge O₄sample that takes on the cubic structure and the maximum size is about 130 nm.Under 265 nm excitation,there exists a broad blue emission belonging to Zn₂Ge O₄matrix and its center wavelength also takes on the blue shift with the increasing concentration.Meanwhile,the intense blue,green and weak orange,red emissions respectively at 490,550,585 and 622 nm are measured,and the optimum doping concentration is 0.7 mol%.The mechanisms of down-conversion photoluminescence and the energy transfer from Zn₂Ge O₄ matrix to Tb³⁺ions are analyzed systematically.Secondly,a series of Tm³⁺,Tb³⁺and Eu³⁺single-doped and co-doped bismuth borosilicate glass?BBSG?have been prepared by using the same method,and the annealing technique is utilized to eliminate the stress within the glass.The excitation and emission spectra of all glass samples are measured,and the photoluminescence characteristics are discussed and the energy transfer processes among the different rare earth ions are analyzed.Under 464 nm excitation,there exists intense red and weak yellow,orange emissions from Eu³⁺:BBSG respectively at 615,580 and 591nm,and the optimum concentration is 1.1 mol%.The intense 455 nm and weak 476nm blue emissions from Tm³⁺:BBSG can be obtained and the optimum concentration is 0.7 mol%under 359 nm excitation.After keeping the same 359 nm excitation,there exist the intense blue,green and red emissions corresponding respectively to455,545 and 615 nm from the BBSG co-doped Tm³⁺,Tb³⁺and Eu³⁺ions.With the increasing concentrations of Tb³⁺ions,its quench phenomenon is not found and the PL intensity belonging to Eu³⁺ions remains almost unchanged.The PL intensity of Tb³⁺ions,however,becomes weaker with the increasing Tb³⁺concentrations,implying that there exists the energy transfer phenomenon from Tm³⁺to Tb³⁺ions.Similarly,the PL intensity from Tm³⁺ions will be unchanged when Tm³⁺concentration is changed,but the PL intensity of Tb³⁺ions also becomes weaker with the increasing Eu³⁺concentrations,which indicates there still exists the energy transfer process between Tb³⁺and Eu³⁺ions.The co-doped BBSG will emit the relatively ideal white light under 359 nm excitation once the molar concentration of Tm³⁺,Tb³⁺and Eu³⁺ions are selected respectively as 0.7:1.1:0.5.The CIE coordinate is?0.3247,0.3402?and the color temperature is 5848 K.It is illustrated that such a kind of BBSG takes on a high-performance white light emission and it is of a potential application prospect for white-light source.