| There has been considerable research on upconverting phosphors since initial interest in the late 1950s. An upconverting phosphor is one which takes multiple photons of lower energy and converts them to one photon of higher energy (this is an anti-Stokes process). Much of the early work was aimed at producing upconverting phosphor lamps by coupling the phosphors with light emitting diodes (LED), though the research did not yield viable products. More recently, there has been a resurgence of interest in upconverting phosphors and an extremely successful and widely utilized photonic application of rare earth elements is in the area of optical fiber-based telecommunications. Fiber optics has been a revolutionary force in the telecommunications industry. The critical component in this application is the Er ion doped fiber amplifier. Recently, the upconverting phosphor technology (UPT) has been applied to produce the lateral flow test strips. Upconverting Phosphor is the same usefull biological label as quantum dot. Upconverting transfer efficiency lies on phonon energy. Phonons are lattice vibrations in a material that can provide nonradiative decay pathways to suppress upconversion luminescence. To overcome the phonon decay problem it is necessary to choose a lattice that has much lower phonon energy. Oxide, fluoride, chloride and fluorochloride compounds are all the suitable materials for this purpose, but fluoride and chloride tend to deliquesce and present poor mechanical properties; and it is difficult to synthesize fluorochloride compounds. Therefor, oxide is often to be chosen as matrices. ZrO2, Y2O3, NaYF4 are suitable matrices with high chemical stabilization. Though NaYF4 is a kind of fluoride, it is still stable as oxide, has very high transfer efficiency. This article studied the three matrices and prepared the corresponding upconverting materials by using new prepared methods, studying their property and the upconverting mechanism. (1) Preparation of ZrO2: Er3+,Yb3+ nanocrystals ZrOCl2·8H2O (AR, Shanghai Chemical Reagent Corp.) and Er2O3 (GR) were used as the starting materials. Er2O3 was dissolved by nitric acid, and then precipitated by ammonia. Erbium acetate was obtained by dissolving the precipitate in acetic acid. To synthesize ZrO2:Er3+ nanoparticles, first, 7.5 g ZrOCl2·8H2O was added to the 80 ml 1,3-butadinol and stirred for 30 min at 200 ℃, then a stoichiometric amount of solid erbium acetate was added into the solution and the system was further stirred for 3 h at 200 ℃. The resulting sol was gelled by the controlled addition of 4 g NaOH. Then the gel particles were separated by centrifugation followed by washing with acetone. The product was dried at 60 ℃in air for 12 h and then calcined at 500 ℃for 2 h. The crystallization temperature is reduced to 500℃. X-ray diffraction (XRD) spectra show there exists monoclinic and cubicZrO2 phases. Green, yellow and red lights are seen from the upconverting luminescence spectra under 980nm excitation. The results confirm that upconverting emission is due to excited-state absorption (ESA) and energy transfer upconverting (ETU) process. (2) Preparation of Y3O2: Er3+,Yb3+ nanocrystals The starting materials are hexamethylenetetramine (AR, Aldrich), Y2O3 (GR), EDTA, Er2O3 (GR), and Yb2O3 (GR). R2O3 (R=Y, Er, Yb) were dissolved by nitric acid, and then precipitared by ammonia. (CH3COO)3R were obtained by dissolving the precipitate in acetic acid. To synthesize Y2O3:Er3+,Yb3+ nanocrystals, first, 1.55 g Yttrium acetate and 2 g EDTA were dissolved in 80 ml water in a beaker and a stoichiometric amount of solid erbium acetate and ytterbium acetate were added in to the solution under a quick stir. Then 20 ml 0.4 M hexamethylenetetramine solution was added and the solution was transparent. The solution was exposed to microwave radiation at a power of 300 W. The microwave irradiation was operated 30 second cycles ( on for 20 s, off for 10 s) until the turbidity was observed. The whole microwave irradiation process will be within 5 minutes. Then the turbidities were separated by centrifugation followed by washing 3 times. The product was dried at 60 ℃in air for 4 h and then calcined at 1000 ℃for 1 h. Erbium, Ytterbium codoped Y2O3 (Y2O3:Er3+,Yb3+) nanocrystals are prepared by microwave method. The reactive time is shortened to several minutes. X-ray diffraction (XRD) spectra show there no crystalline change when the fired temperature varies or doped concentration changes. The results confirm that what influences the color of emission is doped concentration and fired temperature. (3) Template Synthesis and Wettability Properties of large-scale...
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