Energy Transfer,tunable Emission And Temperature Sensing Performance Of Bi³⁺,Eu³⁺ Co-doped Phosphors

As the fourth-generation lighting source,white light-emitting diodes?WLED?have attracted much attention because of their numerous advantages such as energy saving,enviro nmental protection,high luminescent efficiency,long lifetime and so on.Currently,a popular solution to realize WLED is combining LED chip with phosphors,which is called phosphors converted WLED?pc-WLED?.However,the commercial WLED has the disadvantages of low color rendering insex and high correlated color temperature.Thus,the single-phase white phosphors excited by ultraviolet radiation have been developed to solve these problems.Therefore,it has becoming a hot area of research to find new high-efficiency phosphors.In addition,glass ceramics are widely studied due to the advantages of the low phonon energy of nanocrystals and the stable structural properties of glass matrix.In this paper,the structural,luminescent,temperature sensing properties of Bi³⁺,Eu³⁺co-doped phosphors and scintillating performances of rare earth doped oxyfluoride glass ceramics were investigated systemically.The main contents are listed as follows:1.The structural and photoluminescent properties of Ba₉Y₂Si₆O₂₄:Bi³⁺,Eu³⁺phosphors:A series of Bi³⁺and Eu³⁺single-doped as well as Bi³⁺,Eu³⁺co-doped Ba₉Y₂Si₆O₂₄ samples were synthesized through a simple high-temperature solid-state reaction method.Their crystal structures,morphologies,luminescent properties,temperature-dependent emission spectra,decay curves and quantum efficiencies were investigated in detail.Upon ultraviolet light excitation,Bi³⁺single-doped samples exhibited blue and green emissions peaking at 408 and 501 nm,corresponding to the³P₁-¹S₀ transition of Bi³⁺ions.The spectral analysis indicated that there were two different luminescent centers of Bi³⁺ions due to different occupancies in Ba₉Y₂Si₆O₂₄ host lattice.And the highest quantum efficiency can reach 64.5%in Ba₉Y₂Si₆O₂₄:0.024Bi³⁺phosphors.The remarkable spectral overlap between the emission spectra of Bi³⁺ions and the excitation spectra of Eu³⁺ions indicated the exist of energy transfer from Bi³⁺to Eu³⁺.The efficient energy transfer from Bi³⁺to Eu³⁺has been investigated in detail and resulted in that tunable and white-light emission can be obtained by modulating Eu³⁺doping concentration.White emission can be realized with the CIE coordinates of?0.357,0.345?and quantum efficiency of 57.6%for Ba₉Y₂Si₆O₂₄:0.024Bi³⁺,0.02Eu³⁺.The above results demonstrate that Ba₉Y₂Si₆O₂₄:Bi³⁺,Eu³⁺may be a potential candidate for ultraviolet?UV?driven white light-emitting diodes?WLED?.2.The temperature sensing properties of Ca₂YZr₂Al₃O₁₂:Bi³⁺,Eu³⁺phosphors:Bi³⁺,Eu³⁺co-doped Ca₂YZr₂Al₃O₁₂ phosphors were synthesized by a conventional solid-state reaction method.The luminescence of Bi³⁺doped Ca₂YZr₂Al₃O₁₂ phosphors,energy transfer from Bi³⁺to Eu³⁺and the temperature sensing properties of Bi³⁺,Eu³⁺co-doped Ca₂YZr₂Al₃O₁₂ samples have been systematically researched.Under the excitation of ultraviolet light,Bi³⁺single doped phosphors gives 313 and 392 nm emission,which origins from the substitutions of Bi³⁺instead of Ca²⁺and Y³⁺sites,respectively.And the blue to red emission colours were adjustable and observed by increasing Eu³⁺content in Bi³⁺,Eu³⁺co-doped Ca₂YZr₂Al₃O₁₂ samples.Relying on different temperature dependent variation tendency,the fluorescence intensity ratio?FIR?values versus temperature present outstanding temperature sensing properties.The absolute and relative sensitivity can be up to 0.826%K^-11 and 0.664%K^-1,respectively.All above results imply that Ca₂YZr₂Al₃O₁₂:Bi³⁺,Eu³⁺phosphors is a potential alternative for optical thermometer.3.The scintillating properties of Ba GdF₅:Tb³⁺glass ceramics:Glass ceramics?GC?with high volume fraction of crystal phase and high density by increasing the proportion of heavy metal fluorides in the composition were designed.And bulk Tb³⁺doped transparent BaGd F₅ glass ceramics with 23.3%crystal volume ratio and density of 4.65 g·cm^-3 have been prepared.The structural,optical and luminescent properties of precursor glass and GC were systematically explored through series of characterization techniques including X-ray diffraction?XRD?,transmittance spectra,transmission electron microscope?TEM?,photoluminescence?PL?spectra and X-ray excited luminescence?XEL?.After heat treatment,both PL emission and XEL intensity of GC are enhanced because of the movement of Tb³⁺ions from the amorphous glass matrix into BaGdF₅ nanocrystals,which possess lower phonon energy and better crystal field.The luminescent quantum efficiency of GC reaches 30.7%and the XEL intensity of GC is around 140%of that of the commercial BGO scintillating crystal.Our results demonstrate that BaGdF₅:Tb³⁺GC may act as efficient scintillator for X-ray detection.