Controllable Synthesis And Luminescence Properties Of Rare-earth Ions(RE³⁺=Dy³⁺,Tb³⁺,Eu³⁺) Doped Gd₂O₃ Phosphors

In this paper,rare earth ions Dy³⁺,Tb³⁺and Eu³⁺doped Gd₂O₃ precursors were synthesized by hydrothermal method（ammonium hydroxide as precipitator）.The phosphor was obtained after calcining precursors 4 h at 1100 ℃.The hydrothermal synthesis conditions（T=120-180 ℃,pH=8-12）,the development of different kinds of fluorescent materials and the effect of particle morphology on the fluorescence properties were analyzed in detail.The influence of energy transfer mechanism and energy transfer effect on fluorescence performance are discussed by using the level characteristics of Gd³⁺and energy transfer process between different ions.The mainly achievements were listed as following:（1）A series of Gd₂O₃:Dy³⁺and Gd₂O₃:Tb³⁺fluorescent materials were developed under hydrothermal conditions T=140 ℃,pH=9.All precursors have similar functional groups and are completely decomposed to oxides at about 485 ℃.XRD proves that the calcined products are（Gd,Dy）₂O₃ and（Gd,Tb）₂O₃ solid solution.Gd₂O₃:Dy³⁺phosphors exhibit excellent yellow emission(⁴F_9/2-⁶H_13/2 transition)at 572 nm upon UV excitation at 275nm wavelength.The quenching concentration of Dy³⁺was 0.8 at.%,whose quenching mechanism is the interaction between Dy³⁺,and quenching mechanism is electric dipole-electric dipole interaction.The fluorescence lifetime of Gd_1.984Dy_0.016O₃ phosphor at 572 nm is⁰.455 ms,and the fluorescence lifetime of Gd₂O₃:Dy³⁺phosphor decreases with the increase of Dy³⁺doping amount.The color coordinates of all samples were located at（⁰.43,⁰.46）,and the color temperature was³490 K.Gd_2（1-x）Tb_2xO₃（x=0.03-0.13）phosphor was prepared by the same method.Under 308 nm wavelength excitation,the sample showed good green light emission（⁵D₄-⁷F₅ transition）at 542 nm,and the quenching concentration was 7 at.%.Analysis shows that the quenching mechanism is the interaction between Tb³⁺,and the quenching type is Tb³⁺to Tb³⁺energy transfer function.（2）In order to further improve the fluorescence properties of Eu³⁺,on the basis of determining the best dosage of Dy³⁺and Tb³⁺,the Gd₂O₃:Dy³⁺/Eu³⁺,Gd₂O₃:Tb³⁺/Eu³⁺phosphor was synthesized by hydrothermal technology（T=140 ℃,pH=9）.All the precursors obtained in this work are rodlike particles,whose diameter is¹00 nm and length is⁵00 nm.Under the monitoring of 611 nm,the Gd₂O₃:Dy³⁺/Eu³⁺phosphor samples show the characteristic excitation peaks of Eu³⁺,Dy³⁺and Gd³⁺simultaneously.It proves that the energy transfer of Gd³⁺→Eu³⁺and Gd³⁺→Dy³⁺→Eu³⁺are present in the system.Under UV excitation of 275 nm,the main emission peak of the sample is located at⁶11 nm,showing excellent red light emission.Both the emission peak intensity and fluorescence lifetime at 572nm are decrease with the increase of Eu³⁺doping amount,which prove that there is energy transfer between Dy³⁺and Eu³⁺.The energy transfer mechanism from Dy³⁺to Eu³⁺was determined to be electric dipole-four dipole interaction.The calculated results indicate that the Dy³⁺→Eu³⁺energy transfer efficiency increased from 51.6%to 91.06%with the Eu³⁺content increasing from 2 at.%to 10at.%.The fluorescence lifetime of Gd_1.904Dy_0.016Eu_0.08O₃ samples at 611 nm is¹.24 ms,and the color coordinates of the phosphors are located at（⁰.65,⁰.34）,and the color temperature is²840 K.Selecting 308 nm as the excitation wavelength of the system,Gd₂O₃:Tb³⁺/Eu³⁺phosphors can obtain effective red emission.The main emission peak is located at 611 nm,which comes from ⁵D₀-⁷F₂ electric dipole transition of Eu³⁺.The characteristic emission peak intensity and fluorescence lifetime of Tb³⁺at 542 nm decreased with the increase of Eu³⁺content.Through theoretical calculation,the energy transfer mechanism of Tb³⁺to Eu³⁺is four dipole-four dipole interaction.When the Eu³⁺doping amount is 1 at.%,the energy transfer efficiency is 98.7%.The fluorescence lifetime of the Gd_1.78Tb_0.14Eu_0.08O₃ sample at 611 nm is¹.73 ms,the color coordinates are located at（⁰.64,⁰.35）,and the color temperature is²439 K.（3）In order to investigate the effect of particle morphology on the fluorescence properties,a series of Gd_1.904Dy_0.016Eu_0.08O₃ and Gd_1.78Tb_0.14Eu_0.08O₃ phosphors were synthesized by changing the hydrothermal condition（T=120-180 ℃,pH=8-12）.When pH=8,the Gd_1.904Dy_0.016Eu_0.08O₃ and Gd_1.78Tb_0.14Eu_0.08O₃ samples are nanotube like.However,when pH39,the target product is rod like,and the length decreases with the increase of pH value.When the pH value increased from 8 to 12,the fluorescence intensity first decreased and then increased,reaching the minimum value at pH=9.The fluorescence lifetime increases with the increase of the pH value of the reaction liquid.When pH=8,changed the hydrothermal temperature（120-180 ℃）,the diameter of nanoscale tube increases and the crystallinity becomes higher.The fluorescence intensity increased with the increase of reaction temperature and reached the maximum at 180 ℃.The fluorescence lifetime does not change with the increase of temperature.When pH=9,the length of nanorods increases with the increase of temperature.The top of the rod is protruding and the directional growth is more obvious.The fluorescence intensity decreases with the increase of the temperature of the reaction solution,and the fluorescence lifetime increases with the increase of temperature.