Near-infrared Upconversion Emission Research Articles

Bioimaging and toxicity assessments of near-infrared upconversion luminescent NaYF 4:Yb,Tm nanocrystals

In vitro or in vivo bioimaging utilizing the upconversion (UC) luminescence of rare earth fluoride nanocrystals (NCs) has attracted much attention, especially for Yb 3+/Tm 3+ doped NCs with a near-infrared (NIR) UC emission at 800 nm. Herein, water-soluble NaYF 4:Yb,Tm NCs with strong NIR UC emission were synthesized with a solvothermal method. In vitro and in vivo bioimaging and toxicity assessments were carried out with HeLa cell and Caenorhabditis elegans ( C. elegans) cases, respectively. NaYF 4:Yb,Tm NCs afforded an efficient NIR image of the HeLa cells with an incubation concentration of 10 μg mL −1, and CCK-8 assay revealed a low cytotoxicity. Fed with Escherichia coli ( E. coli) and NCs together, the C. elegans showed a NIR image in the gut from the pharynx to the anus. Further, these NCs could be excreted out when those worms were then fed with only E. coli. Toxicity studies were further addressed with protein expression, life span, egg production, egg viability, and growth rate of the worms in comparison with those of the intact ones. The feeding of rare earth fluoride NCs with a dose of 100 μg does not arise obvious toxicity effect from the growth to procreation. The in vitro and in vivo studies confirm that NaYF 4:Yb,Tm NCs could be served as an excellent NIR emission bioprobe with low toxicity.

Lanthanum Silicate and Lanthanum Zirconate Nanoparticles Co-Doped with Ho3+and Yb3+: Matrix-Dependent Red and Green Upconversion Emissions

Excitation of Ho3+ and Yb3+ co-doped lanthanum silicate and lanthanum zirconate nanoparticles with 980 nm diode laser light gave a red and green glow, respectively, observable by naked eye. Spectroscopic investigations on these materials revealed green (540 nm), red (660 nm), and near-infrared (750 nm) upconversion emissions with the green to red ratio varying with the matrix type and the dopant ion (Yb3+) concentration. The emission was predominantly red for Ho3+:Yb3+ (1:3) in lanthanum silicate nanoparticles, while it was predominantly green for Ho3+:Yb3+ (1:7) in lanthanum zirconate nanoparticles. A mechanism involving cross-relaxations and energy back transfer has been proposed to explain the observed behavior. The predominance of red emission has been attributed to a strong quenching of Ho3+ green emitting level mainly by energy back transfer from Ho3+ to Yb3+ on the basis of the near-infrared (NIR) emission spectral analysis.

Bright upconversion white light emission in transparent glass ceramic embedding Tm3+∕Er3+∕Yb3+:β-YF3 nanocrystals

Intense red (Er3+:F9∕24→I15∕24, Tm3+:G41→F43), green (Er3+:H11∕22, S3∕24→I15∕24), and blue (Tm3+:D21→F43, G41→H63) upconversion emissions were simultaneously generated in the transparent glass ceramics containing Tm3+∕Er3+∕Yb3+:β-YF3 nanocrystals under single 976nm laser excitation. It was demonstrated that Tm3+ behaves as the sensitizer for red luminescence of Er3+ and Er3+ as the quenching center for blue, red, and near-infrared upconversion emissions of Tm3+. Various colors of the luminescence, including perfect and bright white light with CIE-X=0.310 and CIE-Y=0.358, can be easily tuned by adjusting the concentrations of the rare earth ions in the material.

Upconversion luminescence in Ho3+/Yb3+- and Tb3+/Yb3+-codoped fluorogermanate glass and glass ceramic

Energy-transfer excited upconversion luminescence in Ho3+/Yb3+- and Tb3+/Yb3+-codoped PbGeO3–PbF2–CdF2 glass and glass–ceramic under infrared excitation is investigated. In Ho3+/Yb3+-codoped samples, green (545nm), red (652nm), and near-infrared (754nm) upconversion emission corresponding to the 5S2(5F4)→5I8, 5F5→5I8, and 5S2(5F4)→5I7 transitions, respectively, was observed. Blue (490nm) emission assigned to the 5F2,3→5I8 transition was also detected. In the Tb3+/Yb3+-codoped system, bright UV–visible emission around 384, 415, 438, 473–490, 545, 587, and 623nm, identified as due to the 5D3(5G6)→7FJ(J=6, 5, 4) and 5D4→7FJ(J=6, 5, 4, 3) transitions, was measured. The comparison of the upconversion process in glass ceramic and its glassy precursor revealed that the former samples present much higher upconversion efficiencies. The dependence of the upconversion emission upon pump power, and doping contents was also examined. The results indicated that successive energy-transfer between ytterbium and holmium ions and cooperative energy-transfer between ytterbium and terbium ions followed by excited-state absorption are the dominant upconversion excitation mechanisms herein involved. The viability of using the samples for three-dimensional solid-state color displays is also discussed.

Upconversion fluorescence of Nd 3+ ions in K 2YF 5 single crystal

Upconversion fluorescence of Nd 3+ ions in K 2YF 5 single crystal was studied under 785-nm (near-infrared), 514.5-nm (green) and 325-nm (ultraviolet) laser excitation. With laser excitation set at 785 nm, a near-infrared upconversion emission band centered at 745 nm with a peculiar linear power dependence was observed and explained successfully by using a multiphonon assisted upconversion mechanism. With 514.5-nm laser excitation, five upconversion emission bands centered at 358, 386, 417, 451 and 496 nm were recorded. The power dependence of these emission bands was also studied and the upconversion mechanism was attributed to the excited state absorption from 4F 3/2 state. In addition, the ultraviolet upconversion fluorescence which peaked at 287 nm under 325-nm laser excitation was also presented and analyzed.