Preparation And Luminescent Properties Of Rare Earth Eu³⁺ Doped Mica-series Layered Silicate

Mineral-based phosphor systems with specific chemical components and intrinsic atomic structure have been rapidly developed recently.In general,it is believed that the studying of the structural model will accelerate the discovery of new compounds and novel phosphor hosts.Actually,many important LED phosphors hosts are practically built upon the existed structural models,especially for the mineral prototype.Moreover,the rare earth doped inorganic layered phosphors have received extensive attention due to their high specific surface area,intrinsic morphology,superior ion-exchange capacity and diverse photofunctional applications.Therefore,it is of great to study the rare earth doped layered clay minerals.In the present work,we report a strategy to enhance the luminescence properties of rare earth Eu³⁺-doped fluorphlogopite?abbreviated as Fpl?through structural modification.During the modification process,the lamellar Fpl was structurally modified by the adjustment of layer charge and the rare earth Eu³⁺ was doped to Fpl with a subsequent high temperature solid state reaction process.The host materials have irregular layered structure,as can be confirmed by the X-ray diffraction patterns and field emission scanning electron microscopy.Under the excitation with 394 and273 nm ultra-violet light,the samples show the characteristic red-light emission of Eu³⁺.Without the pre-modification to Fpl,the luminescence was very weak even after lengthy sintering.However,after the structure of the samples was modulated,the Eu³⁺-doped system exhibited remarkably enhanced emission excited with 394 nm,and the optimal luminescence intensity reached nearly 3-4 fold in comparison with the original samples.It has been noticed that the interlayer spacing of modified Fpl is decreased as compared with the original Fpl due to the ionic radius difference between K+ and Na+.The result suggests that adjustment of layer charge of Fpl is beneficial to enhance the luminescence intensity excited with near UV light,and the layered system may be a potential red light component for the use of solid-state lighting and other opto-electronic devices.Although the overall structural arrangement of Fpl is rather simple,theircomplexity arises to the wide variety of isomorphic substitutions that can occur within the aluminosilicate layers,For example,the exchangeable interlayer K+ cations which compensate the net negative charge can be replaced by Ba2+,and the charge density of tetrahedral sheets can be adjusted by changing the ratio of Si/Al.As a result,the strength of the electric field and the interaction forces between sheet and interlayer cations would be different.In this paper,we also prepared a series of KMg_3-x/2Al_1-xSi_3+xO₁₀F₂:Eu³⁺ and Ba_0.5Mg_3-x/2Al_1-xSi_3+xO₁₀F₂:Eu³⁺ with variable charge of tetrahedral?SiO₄?and octahedral?MgO₆?sheets,and the effect of the [SiO₄],[MgO₆] and interlayer cations on the luminescence behavior of the obtained micas was investigated.It is well-known that the ⁵D₀-⁷F₂ transition of Eu³⁺ is hypersensitive to the crystal field environment.Therefore,a red phosphor with high efficiency excited with near ultraviolet light can be achieved by isomorphic substituting of host materials.