Li+离子掺杂Gd2O3：Sm3+纳米晶的发光增强

采用燃烧法制备了Gd₂O₃:Sm³⁺和Li⁺离子掺杂的Gd₂O₃:Sm³⁺纳米晶,根据X射线衍射图谱确定所得纳米样品为纯立方相。在室温下,用275 nm和980 nm激发光激发各样品时,可分别观测到Sm³⁺离子的强荧光发射和上转换特征发射,其主发射峰分别位于560,602,650 nm处,分别对应着Sm³⁺离子的⁴G_5/2→⁶H_5/2,⁴G_5/2→⁶H_7/2和⁴G_5/2→⁶H_9/2的电子跃迁,其中以⁴G_5/2→⁶H_7/2跃迁的光谱强度最大。实验表明Li⁺离子的掺入使得Sm³⁺离子的荧光发射强度显著增加。通过对样品的XRD、TEM和激发光谱、发射光谱的研究,分析了引起样品荧光强度变化的原因。

Enhanced Photoluminescense of Gd_2O_3:Sm~(3 ) Nanocrystals by Li~ Doping

The luminescence properties of nanosized lanthanide oxide materials have attracted extensive interest because of their fundamental and technological importance.Gd₂O₃,which is easily obtained due to abundant resource in nature,has been widely used as host material.The emission efficiency of Sm³⁺ associated with the intra-4f-shell transition is very high,and it earl emit bright light under both ultraviolet and infrared excitation.Therefore,it often plays a very important role in many luminescent materials.In this paper, Gd₂O₃:Sm³⁺ and Li⁺-doped Gd₂O₃:Sm³⁺ nanocrystals were prepared by a combustion method.The pure nanocrystals were obtained after annealing at 800℃,and the crystallinity was improved with increasing annealing temperature.Both Gd₂O₃:Sm³⁺ and Li⁺-doped Gd₂O₃:Sm³⁺ nanocrystals appeared to be cubic crystal-line phase according to the XRD results.In contrast to Gd₂O₃:Sm³⁺ which showed an irregular shape of ag-glomerated fine particles,the morphology of Li⁺-doped Gd₂O₃:Sm³⁺ nanocrystals were spherical and quite regular.These particles were measured to be about 50 nm in diameter.When excited at 275 nm and 980 nm, Gd₂O₃:Sm³⁺ and Li⁺-doped Gd₂O₃:Sm³⁺ nanocrystals exhibit similar emission spectra,which consist of the characteristic emission bands of the Sm³⁺ ions (⁴G_5/2→⁶H_J,J=5/2,7/2,9/2 transitions at 560,602,650 nm in the spectra) due to an efficient energy transfer from the Gd₂O₃ host lattice to the doped Sm³⁺ ions.It was found that the incorporation of Li⁺ into the Gd₂O₃:Sm³⁺ nanocrystals has greatly enhanced the photolumi-nescence intensity of Sm³⁺ in both photoluminescence and upconversion emission.The highest emission inten-sity was observed with Gd_1.83Li_0.15Sm_0.02O₃,whose brightness was increased by a factor about 7.0 in comparison with that of Gd₂O₃:Sm³⁺.As we all known that defects of the surface of the nanoparticles,which provide non-radiation recombination routes for electrons and holes,often act as non-radiative centers and has great influence on luminescent properties.It can be suggested that the incorporation of Li⁺ can greatly decrease the deficiencies and oxygen vacancies.That is,the defects and oxygen vacancies of the surface of nanoparticles decreased at first when Li⁺ content was lower,which decreased the luminescence quenching centers and increased the crystallinity,thereby enhanced the emission intensity.A lot of defects could be induced in the system with a gradual increase of Li⁺ content.This will destroy the crystallinity and thus lead to the luminescence quenching.In conclusion,this paper reported the correlation between the morphology,structure and optical behaviors on Gd₂O₃:Sm³⁺ nanocrystals doped with Li⁺ Li⁺ doping at a low content significantly improved the morphology of phosphors and strongly enhanced the luminescent properties.