The Synthesis And Properties Of Gd₂O₂SO₄:Ln³⁺/Gd₂O₂S:Ln³⁺ Luminescent Materials

At present,GOS scintillation ceramics prepared with Gd₂O₂S as matrix material has a deep practical significance in X-ray intensifying screen,X-ray Computed Tomography?X-CT?,Positron Emission Tomography?PET?and so on.Gd₂O₂S can be obtained by Gd₂O₂SO₄reduction,which is used as the raw material for the sintering of GOS scintillation ceramics.The morphology,size and dispersion of the powder directly affect the scintillation performance of GOS scintillation ceramics.Therefore,it is very important to study the preparation methods and luminescent properties of Gd₂O₂SO₄:Ln³⁺/Gd₂O₂S:Ln³⁺luminescent materials.The main research content can be summarized as follows:Gd?NO₃?₃·6H₂O,Tb?NO₃?₃·6H₂O,L-Cysteine and urea were used as experimental starting materials.Among them L-Cysteine and urea were as sulfur source and precipitator,respectively.The precursor was synthesized by hydrothermal reaction at 150?for 24 h,which was then converted into green ribbon-like Gd₂O₂SO₄:Tb³⁺luminescent materials through calcined at 800?for 2 h in air.It was demonstrated that pure Gd₂O₂SO₄phase could be obtained when Gd?NO₃?₃,L-Cysteine and urea were mixed in accordance with the molar ratio of 1:2:0.25.The as-obtained Gd₂O₂SO₄:Tb³⁺is uniform size with 0.8?m in width,and the formation mechanism of Gd₂O₂SO₄:Tb³⁺phase has also been proposed.Gd₂O₂SO₄:6%Tb³⁺had the strongest green emission at 544 nm under230 nm UV light excitation,which corresponded to the ⁵D₄?⁷F₅ transition of Tb³⁺ions.These results suggested that the Gd₂O₂SO₄:Tb³⁺luminescent materials might have potential applications in X-ray intensifying screens,fluorescence and scintillation material fields.The multicolor hollow spheres Gd₂O₂S:x Tb³⁺,y Eu³⁺luminescent materials were successfully synthesized at 220?for 16 h via a solvothermal route with commercially available Ln?NO₃?₃·6H₂O?Ln=Gd,Tb and Eu?,absolute ethanol,ethanediamine and sublimed sulfur as the starting materials.Hollow sphere structure has a typical size of about 2.5?m in diameter and about 0.5?m in shell thickness.The possible formation mechanism depending on synthetic time for the Gd₂O₂S phase has been presented.Photoluminescence?PL?spectra reveal that the strongest emission peak for the Gd₂O₂S:x Tb³⁺and the Gd₂O₂S:y Eu³⁺samples is located at 545 and 628 nm,corresponding to ⁵D₄?⁷F₅transitions of Tb³⁺ions and ⁵D₀?⁷F₂transitions of Eu³⁺ions,respectively.The quenching concentration of Tb³⁺and Eu³⁺ions is 7%.In the case of Tb³⁺and Eu³⁺co-doped samples,when the concentration of Tb³⁺or Eu³⁺ions is 7%,the optimum concentration of Eu³⁺or Tb³⁺ions is determined to be 1%.Under 254nm UV light excitation,the Gd₂O₂S:7%Tb³⁺,the Gd₂O₂S:7%Tb³⁺,1%Eu³⁺and the Gd₂O₂S:7%Eu³⁺samples give green,yellow and red emissions,respectively.And the corresponding CIE coordinates vary from?0.3513,0.5615?,?0.4120,0.4588?to?0.5868,0.3023?.Gd₂O₂S luminescent materials can achieve different color luminescence by adjusting the type and concentration of doped rare earth ions,which can be applied to optical displays,fluorescent microprobe,biomedicine multi-color displays and so on.Commercially available rare earth nitrate?Ln?NO₃?₃·6H₂O?Ln=Gd,Pr and Ce??,urea,sodium sulfite?Na₂SO₃?,ammonium sulfate??NH₄?₂SO₄?and carbon powder were used as the starting materials.The precursor was synthesized at 95?for 4 h by homogeneous precipitation method,and then the hexagonal with about 1?m in size Gd₂O₂S:Pr³⁺,Ce³⁺luminescent materials were prepared at 1000?for 2 h in sealed environment by triple-crucible method.The PL spectra under 301 nm UV light excitation shows a strong green emission at 513 nm,which matches the ³P₀?³H₄ transition of Pr³⁺ions.The quenching concentration occurs at Pr³⁺ions concentration of 0.2%and its corresponding CIE coordinates is?0.0273,0.7921?.The decay lifetimes are?₁=0.248?s and?₂=1.824?s for the Gd₂O₂S:0.2%Pr³⁺,Ce³⁺.The Gd₂O₂S:0.2%Pr³⁺,Ce³⁺film has excellent performance in the light utilization and the charge-transfer capability under 270 nm UV light radiation.The triple-crucible method provides a reference for the preparation of other rare earth oxysulfides.