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Abstract. Er3+/Yb3+ codoped pyrochlore-type yttrium titanate (Y0.985-xEr0.015Ybx)2Ti2O7 (x=2.5 %, 5.0 %, 7.5 %, 10.0 % and 12.5 %) nanopowders were successfully prepared by the Pechini-type sol−gel process with citric acid as chelating ligands and polyethylene glycol as cross-linking agent. The preparation process was monitored by X-ray diffraction, thermal-gravimetric differential thermal analysis and Fourier transform-infrared experiments and the microstructures and morphologies of as-prepared samples were characterized by transmission electron microscopy and high resolution transmission electron microscopy images. Detailed proofs showed that the samples annealed at 800 C for 1 h exhibit good crystallinity, dispersibility and narrow size distribution with average size of 20-30 nm. For all the Er3+/Yb3+ codoped pyrochlore-type (Y0.985-xEr0.015Ybx)2Ti2O7 nanoparticles, bright visible upconversion emission for all the samples can be clearly observed with naked eyes under 980 nm excitation at room temperature. As for amorphous (Y0.91Er0.015Yb0.075)2Ti2O7 samples, upconversion spectra exhibit the two broad erbium emission bands centered at approximately 546 nm and 660 nm, which are ascribed to the 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions, respectively, and relatively weaker broad emission bands at about 524 nm, which is attributed to 2H11/2→4I15/2 transitions. As the annealing temperature increases, there exits Stark splitting effects, and the upconversion luminescence intensities increase, whih was attributed to the removal of the hydroxyl groups and to the decrease of the surface area caused by the growth of the nanoparticles. There exists the optimal Yb3+ ion concentration of 7.5 mol % doping in (Y0.985-xEr0.015Ybx)2Ti2O7 nanocrystals which can give rise to a maximum upconversion luminescence intensity. These are the efficient upconversion nanophosphors. 3.4 TEM spectra Transmission electron microscopy (TEM) was employed to obtain direct information about the size and structure of the as-prepared Er3+ /Yb3+ cooped (Y0.91Er0.015Yb0.075)2Ti2O7 nanocrystals. The typical TEM results of (Y0.91Er0.015Yb0.075)2Ti2O7 nanocrystals prepared at 800C for1 h are shown in Fig. 5. From Fig. 5(a), it can be found that quasi-spherical nanopowders have good dispersibility, and the average size estimated from TEM is around 20-30 nm, which is quite consistent to above-mentioned XRD results. The insert in Fig. 5(a) shows the corresponding selected-area electron diffraction (SAED) patterns, which is the characteristic rings of nano-polycrystals. In Fig. 5b, the typical high-resolution transmission electron microscopy (HRTEM) images indicate the clear and regular crystal lattice distance suggesting that highly crystalline (Y0.91Er0.015Yb0.075)2Ti2O7 were formed. The lattice fringes with the interplanar distance of 0.292 nm obtained from the HRTEM images was attributed to the (222) plane of the cubic structure. 4. Conclusion Abstract. Er3+/Yb3+ codoped pyrochlore-type yttrium titanate (Y0.985-xEr0.015Ybx)2Ti2O7 (x=2.5 %, 5.0 %, 7.5 %, 10.0 % and 12.5 %) nanopowders were successfully prepared by the Pechini-type sol−gel process with citric acid as chelating ligand and polyethylene glycol as cross-linking agent. The samples annealed at 800 C for 1 h exhibit good crystallinity, dispersibility and narrow size distribution with average size of 20-30 nm; And also, there exists the optimal Yb3+ ion concentration of 12.5 mol % doping in (Y0.985-xEr0.015Ybx)2Ti2O7 nanocrystals which can give rise to a maximum upconversion luminescence intensity. The increase of the upconversion luminescence intensities with the calcination temperature was attributed to the removal of the hydroxyl groups and to the decrease of the surface area caused by the growth of the nanoparticles. |
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sltmac
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【答案】應(yīng)助回帖
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ringzhu(金幣+2): O(∩_∩)O~ 2011-06-03 10:28:50
ringzhu(金幣+30): ~~ 2011-06-06 15:44:20
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摘要：通過佩基尼溶膠凝膠法，檸檬酸和聚乙二醇分別作為螯合配體和交聯(lián)劑成功制備出了Er3+/Yb3+共摻雜焦綠石型鈦酸釔(Y0.985-xEr0.015Ybx)2Ti2O7 (x=2.5 %, 5.0 %, 7.5 %, 10.0 % 和 12.5 %)納米粉體。制備過程通過XRD、TG-DSC和FTIR考察，合成樣品的微結(jié)構(gòu)和形貌通過TEM和HRTEM表征。詳細(xì)的實(shí)驗(yàn)結(jié)果表明樣品C經(jīng)1h處理后顯示了好的晶型、分散度已經(jīng)平均粒徑在20-30nm的窄的分布。對所有的Er3+/Yb3+共摻雜焦綠石型鈦酸釔(Y0.985-xEr0.015Ybx)2Ti2O7納米粒子來說，室溫下樣品的可見光上轉(zhuǎn)換光譜發(fā)射可在980nm激發(fā)態(tài)處清楚地觀察到。對于無定形的(Y0.91Er0.015Yb0.075)2Ti2O7樣品來說，在大約546nm和660nm處顯示了兩個寬的鉺上轉(zhuǎn)換光譜發(fā)射帶，這可以分別用電子從4S3/2→4I15/2以及4F9/2→4I15/2遷移的機(jī)理解釋。隨著煅燒溫度的升高，會出現(xiàn)Stark分裂效應(yīng)，上轉(zhuǎn)換發(fā)光強(qiáng)度增大，這是由于羥基的去除以及納米粒子的長大從而導(dǎo)致表面積減小引起的。Yb3+摻雜(Y0.985-xEr0.015Ybx)2Ti2O7納米晶的最佳濃度在7.5 mol %，此濃度下上轉(zhuǎn)換發(fā)光強(qiáng)度最大。 3.4 TEM圖譜 用TEM可以直接得到制備出Er3+ /Yb3+共摻雜(Y0.91Er0.015Yb0.075)2Ti2O7納米晶體尺寸和結(jié)構(gòu)的信息。樣品C經(jīng)800℃、1h處理的TEM圖如圖5所示，可以看到近球狀的納米粉體有著好的分散度，從TEM可以看到平均粒徑在20-30nm，這與XRD的結(jié)果一致。圖5（a）的插圖是選區(qū)分析圖譜（SAED），是納米晶的特征環(huán)。圖5b中，HRTEM顯示(Y0.91Er0.015Yb0.075)2Ti2O7形成了清晰、具有周期性的晶體結(jié)構(gòu)，其晶格兼具也說明了晶型的形成。晶面間距離0.292nm對應(yīng)著立方結(jié)構(gòu)的（222）面。 4 結(jié)論 |
2樓2011-05-29 10:40:33
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3樓2011-05-29 10:41:57
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