Li^+离子掺杂Gd_2O_3：Sm^(3+)纳米晶的发光增强

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

采用燃烧法制备了Gd_2O_3:Sm^(3+)和Li^+离子掺杂的Gd_2O_3:Sm^(3+)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Sm^(3+)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Sm^(3+)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Sm^(3+)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。

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 Sm^3＋ associated with the intra-4f-shell transition is very high, and it can 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：Sm^3＋ and Li^＋-doped Gd2O3：Sm^3＋ 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：Sm^3＋ and Li^ ＋-doped Gd2O3：Sm^3＋ nanocrystals appeared to be cubic crystalline phase according to the XRD results. In contrast to Gd2O3：Sm^3＋ which showed an irregular shape of agglomerated fine particles, the morphology of Li^＋ -doped Gd2O3：Sm^3＋ 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：Sm^3＋ and Li ^＋ -doped Gd2O3：Sm^3＋ nanocrystals exhibit similar emission spectra, which consist of the characteristic emission bands of the Sm^3 ＋ ions （^4G5/2→6HJ,J=5/2,7/,2, 9/2 transitions at 560,602,650 nm in the spectra） due to an efficient energy transfer from the Gd203 host lattice to the doped Sm^3＋ ions. It was found that the incorporation of Li^＋ into the Gd2O3： Sm^3＋ nanocrystals has greatly enhanced the photoluminescence intensity of Sm^3＋ in both photoluminescence and upconversion emission. The highest emission intensity was observed with Gd1.83Li0.15Sm0.02O3, whose brightness was increased by a factor about 7.0 in comparison with that of Gd2O3：Sm^3＋. 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 in- fluence 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 in- creased the crystallinity, thereby enhanced the emission intensity. A lot of defects could be induced in the sys- tem 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：Sm^3＋ nanocrystals doped with Li ^＋ Li^＋ doping at a low content significantly improved the morphology of phosphors and strongly enhanced the luminescent properties.