基于层状氢氧化镧的稀土离子激活杂化组装荧光体

Rare Earth Ions-Activated Hybrid Assemblies Fluorescent Systems Based on the Layered Lanthanum Hydroxides

采用水热法制备了十二烷基磺酸根(DS−)插层的稀土离子(Eu^(3+),Tb^(3+)和Ce^(3+))激活的层状氢氧化镧(LLaH),通过微波法将苯甲酸根(BA−)与层中DS−进行离子交换反应,形成杂化组装.X-射线衍射(XRD)结果表明这些杂化组装具有典型的层状结构,离子交换反应后层间距由3.2 nm减小为1.9 nm.光致发光光谱显示稀土Eu^(3+)和Tb^(3+)掺杂的LLaH均表现出相应的特征红色和绿色发射,但(Eu/Tb)_(0.1)La_(1.9)(OH)_(5)BA·H_(2)O的发光强度是(Eu/Tb)_(0.1)La_(1.9)(OH)_(5)DS·H_(2)O的十几倍,这得益于BA−对稀土离子发光产生了很好的敏化作用.通过超声和离心过程将Tb_(0.1)La_(1.9)(OH)_(5)BA·H_(2)O,Eu_(0.1)La_(1.9)(OH)_(5)BA·H_(2)O和Ce_(0.08)La_(1.92)(OH)_(5)DS·H_(2)O杂化组装样品进行层剥离制成胶体溶液,发现不同比例的Eu_(0.1)La_(1.9)(OH)_(5)BA·H_(2)O和Tb_(0.1)La_(1.9)(OH)_(5)BA·H_(2)O两种胶体混合能够对发光颜色进行调整;三种胶体混合后通过改变激发波长也可以有效调整发光颜色,特别是在280~290 nm紫外光激发下,能够获得白色荧光,显示出优异的光功能特性.

The layered rare earth hydroxides(LRHs)have recently been paid attention owing to the adjustable rare earth ions in the host and alterable anions in the gallery,which may be applied in adsorption,catalyst,fluorescence and detection fields.However,as far as we know,the studies of rare earth ions-activated layered lanthanum hydroxide(LLaH)fluorescent systems were seldom reported.In this paper,the hybrid assemblies(Eu/Tb) _(0.1)La_(1.9)(OH)_(5)DS·H_(2)O and Ce_(0.08)La_(1.92)(OH)_(5)DS·H_(2)O solid samples were first prepared with Eu(NO_(3))3,TbCl_(3),Ce(NO_(3))3·6H_(2)O and La(NO_(3))3 solutions by hydrothermal pro-cess at 140℃for 12 h,in which the interlayer was pillared with dodecyl sulfonate(DS−)anions.Then,the DS−anions of the as-prepared(Eu/Tb) _(0.1)La_(1.9)(OH)_(5)DS·H_(2)O were exchanged with benzoate(BA−)solution through microwave process,and the hybrid assemblies samples(Eu/Tb) _(0.1)La_(1.9)(OH)_(5)BA·H_(2)O were obtained.The X-ray diffraction(XRD)results indicate that the solid samples have superior crystallization and layered structure,and the interlayer distance is decreased from 3.2 nm to 1.9 nm after the ion-exchange reaction.The photoluminescence excitation spectra show that the excitation intensities in the ultraviolet(UV)region(≈280 nm)for(Eu/Tb) _(0.1)La_(1.9)(OH)_(5)BA·H_(2)O are much stronger than those for(Eu/Tb) _(0.1)La_(1.9)-(OH)_(5)DS·H_(2)O due to the strong absorption peak from BA−anion.Excited with 280 nm,the emission spectra exhibit the characteristic emission transitions of Eu^(3+)or Tb^(3+)ions,and the intensities of(Eu/Tb) _(0.1)La_(1.9)(OH)_(5)BA·H_(2)O are more than tenfold of(Eu/Tb) _(0.1)La_(1.9)(OH)_(5)DS·H_(2)O because of efficient sensitization effect of BA−.On the other hand,the(Eu/Tb) _(0.1)La_(1.9)(OH)_(5)BA·H_(2)O and Ce_(0.08)La_(1.92)(OH)_(5)DS·H_(2)O hybrid assemblies were exfoliated to colloidal solutions through ultrasound and centrifugation process in formamide solvent.It has been observed that the fluorescent color can be adjusted by mixing the colloid solutions of Eu _(0.1)La_(1.9)(OH)_(5)BA·H_(2)O and Tb _(0.1)La_(1.9)(OH)_(5)BA·H_(2)O in different volume ratios.Moreover,the fluorescent color can be changed with the three colloid components by varying the excitation wavelength.In particular,the white light can be achieved as excited with 280—290 nm UV light,exhibiting supreme photofunctional performances.