Synthesis And Luminescence Properties Of Rare-earth Ions Doped Gd₃Al₅O₁₂ As Colorful Phosphors

The precursor of rare earth ions(RE³⁺: Tb³⁺,Tb³⁺/Dy³⁺,Tb³⁺/Eu³⁺ and Tb³⁺/Ce³⁺)doped aluminum gadolinium garnet(Gd₃Al₅O₁₂,GdAG)were synthesized by co-precipitation method using ammonium hydrogen carbonate as precipitating agent.The GdAG:RE³⁺ solid solution were acquired by the following calcination.Coprecipitation synthesis,crystal structure stabilization and fluorescent properties of Gd AG:RE³⁺ phosphors were detailed discussed in this work.The fluorescence properties of activator ions were enhanced via the different energy levels matching with Gd³⁺.The effect of morphology,rare earth ions and energy transfer on the fluorescence properties of GdAG:RE³⁺ phosphors were discussed in detail and the mainly innovative achievements were listed as following:?1?The crystal structure of GdAG can be stabilized by doping smaller Tb³⁺ of 7 at.% and the decomposition of GdAG was againsted by calcining at 1500 oC.The precursor of GdAG:Tb³⁺ were systhesizede by co-precipitation method using the rare earth nitrates as mother salt and ammonium hydrogen carbonate as precipitating agent.The chemical formula of the precursor were expressed as ?NH₄?_x Ln₃Al₅?OH?_y?CO₃?_z·nH₂O via the FT-IR analysis.The Ln₄Al₂O₉ monoclinic?LnAM?,LnAlO₃ perovskite?Ln AP?,and LnAG garnet were formed gradually with the calcination temperature increasing and the pure garnet phase was abtained at 1500 oC for 4h.All the precursor obtained in this work is loosely agglomerated and composed of much finer primary particles up to ⁴0 nm in size.The oxide crystallites/particles tend to be elongated and significant coarsening takes place,but relatively good dispersion of the particles persisted even at high temperature of 1500 °C.The?Gd1-xTbx?AG powders exhibit characteristic emission of Tb³⁺ peak at ⁴92 nm(⁵D₄?⁷F₆ transition of Tb³⁺,blue),⁵44 nm(⁵D₄?⁷F₅ transition of Tb³⁺,green),⁵92 nm(⁵D₄?⁷F₄ transition of Tb³⁺,orange-red)and ⁶25 nm(⁵D₄?⁷F₃ transition of Tb³⁺,red)upon UV excitation at 277 nm(4f⁸?4f⁷5d¹ transition of Tb³⁺),and the quenching concentration of Tb³⁺ was found to be ¹0 at.%.And the emission intensity of(Gd_0.9Tb_0.1)AG under 277 nm excitation were higher than(Y_0.9Tb_0.1)AG and(Lu_0.9Tb_0.1)AG garnets due to the Gd³⁺?Tb³⁺efficient energy transfer.The 544 nm green emission decays in a single exponential manner,and successively shorter lifetime was found with the Tb concentration increasing.Under the optimum Tb content of 10 at.%?x=0.1?and the same synthesis condition,though the(Gd_0.9Tb_0.1)AG phosphors have the almost identical lifetime to the(Y_0.9Tb_0.1)AG and(Lu_0.9Tb_0.1)AG system.?2?The metastable Gd₃Al₅O₁₂ could be stabilized by doping smaller Tb³⁺ ions of 10 at.%.Based on this,the(Gd_0.9-xTb_0.1Dy_x)₃Al₅O₁₂(x=0-0.04,GdAG:Tb³⁺/Dy³⁺)solid solution was acquired by calcining their respective precursor prepared via co-precipitation method at 1500 oC in order to further improve the green emission of Tb³⁺.Under the optimal UV excitation of 275 nm,the GdAG:Tb³⁺/Dy³⁺ phosphors exhibit characteristic emission of Tb³⁺ at ⁴96 nm?blue?,⁵48 nm?green?,⁵90 nm?orange-red?and ⁶28 nm?red?which were attributed to the ⁵D₄?⁷F_J?J=6,5,4,3?transition of Tb³⁺.Compared to the Dy³⁺-free(Gd_0.9Tb_0.1)AG phosphor,the emission intensity of Dy³⁺-doped phosphors display stronger owing to the efficient energy transfer from Dy³⁺ to Tb³⁺.The optimal amount of Dy³⁺ in GdAG:Tb³⁺/Dy³⁺ phosphors was determined to be ².5 at.%?x=0.025?.?3?The metastable Gd₃Al₅O₁₂ could be stabilized by doping smaller Tb³⁺ ions of 10 at.%,based on this,the larger Eu³⁺ was doped to adjust the emission color.The GdAG:Tb³⁺/Eu³⁺ phosphor were successfully prepared via co-precipitation method at 1500 oC.Under 276 nm excitation,the phosphors exhibited both Tb³⁺ and Eu³⁺ emissions at 548 nm(green,⁵D₄?⁷F₅ transition of Tb³⁺)and 592 nm(orange-red,⁵D₀?⁷F₁ transition of Eu³⁺),respectively.The emission intensity of Tb³⁺ gradually decreased with the Eu³⁺ addition owing to the efficient Tb³⁺?Eu³⁺ energy transfer and the emission color can be readily tuned from approximately green to orange-red.From the quantum efficiency of(Gd_0.9-x Tb_0.1Eu_x)AG phosphors it can be seen that with the Eu³⁺ content increasing,both the external??ex?and internal??in?quantum efficiency increase up to 1 at.%?x=0.01?and then gradually decrease.Owing to the Tb³⁺?Eu³⁺ energy transfer,the lifetime for the 548 nm emission of Tb³⁺ decreased with the Eu³⁺ increasing.The calculated results indicate that the Tb³⁺?Eu³⁺ energy transfer efficiency increased from 17.2% to 45.54% with the Eu³⁺ content increasing from 0.005 to 0.03.?4?The?Gd,Y?AG:Tb³⁺/Ce³⁺ phosphor were synthesized by co-precipitation method and following by calcination at 1300 oC in order to increase the red parts of the YAG:Ce³⁺.The metastable GdAG could be stabilized by doping 10 at.%Y³⁺,and Tb³⁺/Ce³⁺ coped phosphors were acquired in this work.The precursor obtained in this work is loosely agglomerated and composed,the particle size was determined about ³00 nm by calcining at 1300 oC.Under the 275 nm and 351 nm UV excitation,the PL spectra included both Tb³⁺ and Ce³⁺ characteristic emission.The intensity of Tb³⁺ emission decreased with the content of Ce³⁺ increasing and the characteristic emission of Tb³⁺ disappeared finally.Under the characteristic excitation wavelength of 452 nm,the?Gd,Y?AG:Tb³⁺/Ce³⁺ phosphor exhibited 5d-4f transition of Ce³⁺ between 475 nm and 750 nm range,and the quenching concentration of Ce³⁺ was found to be ¹ at.%.The lifetime of Ce³⁺ at 546 nm decreased from 4.08±0.01 ms to 0.70±0.01 ms with the content of Ce³⁺ increasing under 275 nm excitation.The energy transfer efficiency from Tb³⁺ to Ce³⁺ increased from 41.67% to 83.82%.The energy transfer mechanism from Tb³⁺ to Ce³⁺ was determined to be electric dipole-electric dipole interaction.