Preparation Of Rare-earth Complexes-based Fluorescent Materials And Their Analytical Applications

Fluorimetry exhibits great advantages, such as high sensitivity, low cost, reasonable selectivity and various analytical parameters. However, traditional fluorescent reagents have some drawbacks such as strong background fluorescence, photobleaching, and so on, which restricts the wider application of fluoremetry. Rare earths have excellent properties including narrow emission profiles, larger stokes shift, long fluorescence lifetime, high quantum yield and good chemical stability. Based on the above points, we synthesized rare-earth-based fluorescent materials, and also investigated their analytical applications.In part one, we chose available and cheap sodium hexametaphosphate as chelate to synthesize Terbium(Ⅲ)-sodium hexametaphosphate (Tb/SHMP). Based on the fluorescence quenching of Tb/SHMP chelates in the presence of chromate (III), a sensitive fluorimetric method was developed for the determination of trace amounts of chromium (III) in aqueous solutions. Under the optimum conditions, the linear range and the detection limit (3σ) for Cr(III) were 7.69×10-7 - 1.15×10- 4 mol L^-1 and 4.5×10-7 mol L^-1, respectively . The method was applied successfully to the determination of chromium (III) in real samples with a satisfactory result.In part two, an efficient luminescence energy transfer (LET) system based on Tb/SHMP chelates as donor and 4-((4-(2-aminoethylamino)naphthalen^-1-yl)diazenyl)benzenesulfonic acid dihydrochloride (ANDBS) as acceptor was developed for the sensitive determination of trace nitrite. Based on the luminescence quench intensity of Tb/SHMP chelates varied with the concentrations of nitrite, a new assay for the selective and sensitive determination of nitrite was developed. Under the optimum conditions, the linear calibration graph was obtained with a linear range of 0.00040 - 0.20μg mL^-1. The detection limit (3σ) was 0.00010μg mL^-1. The method was applied successfully to the determination of nitrite in synthetic samples.In part three, we successfully synthesized hexagonal phase NaYF₄:Yb³⁺, Er³⁺ upconversion nanocrystals by hydrothermal method. The nanopariticles display green emssion and easy dispersion in water. With NaYF₄:Yb³⁺, Er³⁺ as donor, a fluorescence energy transfer system for selective determination of nitrite ions was developed. The detection limit for nitrite achieved is 0.0046μg mL^-1 and the system shows high sensitivity towards nitrite at 0.0080 - 0.25μg mL^-1 range.