Upconversion and Anti-Stokes Processes with f and d Ions in Solids

Shape, size, and phase-controlled rare-Earth fluoride nanocrystals with optical up-conversion properties

High-quality rare-earth fluorides, alpha-NaMF(4) (M=Dy, Ho, Er, Tm, Y, Yb, and Lu) nanocrystals and beta-NaMF(4) (M=Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y, Yb, and Lu) nanoarrays, have been synthesized by using oleic acid as a stabilizing agent through a facile hydrothermal method at 130-230 degrees C. The phase, shape, and size of the products are varied by careful control of synthetic conditions, including hydrothermal temperature and time, and the amounts of reactants and solvents. Tuning the hydrothermal temperature, time, and the amount of NaOH can cause the transformation from the cubic alpha-NaMF(4) to hexagonal phase beta-NaMF(4). Upon adjustment of the amount of NaOH, NaF, M(3+), and ethanol, the morphologies for the beta-NaMF(4) nanoarrays can range from tube, rod, wire, and zigzagged rod, to flower-patterned disk. Simultaneously, the size of the rare-earth fluoride crystals is variable from 5 nm to several micrometers. A combination of "diffusion-controlled growth" and the "organic-inorganic interface effect" is proposed to understand the formation of the nanocrystals. An ideal "1D growth" of rare-earth fluorides is preferred at high temperatures and high ethanol contents, from which the tube- and rodlike nanoarrays with high aspect ratio are obtained. In contrast, the disklike beta-NaMF(4) nanoarrays with low aspect ratios are produced by decreasing the ethanol content or prolonging the reaction time, an effect probably caused by "1D/2D ripening". Multicolor up-conversion fluorescence is also successfully realized in the Yb(3+)/Er(3+) (green, red) and Yb(3+)/Tm(3+) (blue) co-doped alpha-NaYF(4) nanocrystals and beta-NaYF(4) nanoarrays by excitation in the NIR region (980 nm).

Monodisperse upconverting nanocrystals by microwave-assisted synthesis

Upconverting nanocrystals have a tremendous potential for applications in fields such as bioanalysis, medical therapy, or display technologies. However, a prerequisite for many applications is the availability of small, monodisperse, and highly luminescent nanocrystals. Here we show, that a microwave-assisted synthesis approach allows for the synthesis of such monodisperse and luminescent upconverting nanocrystals within 5 min in a closed reaction vessel. Even though the same reactants and solvents as with classical conductive heating reactions were used, microwave-assisted synthesis resulted in differently sized and shaped particles and provided superior reaction control. The nucleation and growth mechanism follows a La Mer scheme and can be controlled extremely accurately. It is expected that the fundamental principles of this synthesis approach can be applied to many other types of nanocrystals as well.

NIR-responsive silica-coated NaYbF(4):Er/Tm/Ho upconversion fluorescent nanoparticles with tunable emission colors and their applications in immunolabeling and fluorescent imaging of cancer cells

NaYbF(4): RE upconversion (UC) fluorescent nanoparticles (NPs) were synthesized with variable rare-earth dopants (RE= Er(3+), Tm(3+), or Ho(3+), or a combination of these ions), from rare-earth stearate precursors in a water-ethanol-oleic acid system by using a two-phase solvothermal method. The NPs were shown to emit visible light such as orange, yellow, green, cyan, blue or pink light in response to near infrared (NIR) irradiation, and their emission colors could be simply tuned by changing either the co-dopant concentration or dopant species. The UC NPs were well-dispersed and spherical with an average size of 15~35 nm. They emitted strong UC fluorescence under the 980 nm NIR excitation. The effects of solvothermal reaction time and temperature on nanoparticle size and phase structure as well as UC fluorescence intensity were systematically studied. Water dispersibility was achieved by forming a silica coat on the surface of the UC NPs. After animo-functionalization, the silica-coated UC NPs were chemically conjugated with the rabbit anti-CEA8 antibody and then used as fluorescent biolabels for the immunolabeling and imaging of HeLa cells. The NIR-responsive multicolor visible light emission of these UC NPs will enable potential applications in biolabeling and multiplexed analysis because NIR light can penetrate tissue as deep as several inches and is safe to human body.

Upconverting nanophosphors for bioimaging

Upconverting nanoparticles (UCNPs) when excited in the near-infrared (NIR) region display anti-Stokes emission whereby the emitted photon is higher in energy than the excitation energy. The material system achieves that by converting two or more infrared photons into visible photons. The use of the infrared confers benefits to bioimaging because of its deeper penetrating power in biological tissues and the lack of autofluorescence. We demonstrate here sub-10 nm, upconverting rare earth oxide UCNPs synthesized by a combustion method that can be stably suspended in water when amine modified. The amine modified UCNPs show specific surface immobilization onto patterned gold surfaces. Finally, the low toxicity of the UCNPs is verified by testing on the multi-cellular C. elegans nematode.

Upconversion emission tuning from green to red in Yb3+/Ho3+-codoped NaYF4 nanocrystals by tridoping with Ce3+ ions

Upconversion (UC) emission tuning from green to red in monodisperse NaYF(4):Yb(3+)/Ho(3+) nanocrystals was successfully achieved by tridoping with Ce(3+) ions under diode laser excitation of 970 nm. It is proposed that two efficient cross-relaxation processes, 5S2/5F4(Ho) + 2F(5/2)(Ce) --> 5F5(Ho) + 2F(7/2)(Ce) and 5I6(Ho) + 2F(5/2)(Ce) --> 5I7(Ho) + 2F(7/2)(Ce)between Ho(3+) and Ce(3+) ions, have been employed to select UC pathways to tune the UC radiation. Theoretical investigations based on steady-state equations demonstrate the proposed UC mechanisms and explain well the observed linear increase of the UC red-to-green intensity ratio with the increment of Ce(3+) ion concentrations.

Ultraviolet and violet upconversion fluorescence of europium (III) doped in YF(3) nanocrystals

Under 980 nm excitation, Eu(3+)/Tm(3+)/Yb(3+) tri-doped YF(3) nanocrystals emitted ultraviolet and visible fluorescence. Besides the upconversion emissions from Tm(3+) ions, not only were the unusual (5)D(2)-->(7)F(3), (5)D(3)-->(7)F(J) emissions of Eu(3+) observed, but also the ultraviolet upconversion luminescence of Eu(3+) from (5)H(3-7), (5)G(2-6), (5)L(6)-->(7)F(0) transitions were recorded. This unique optical property was attributed to the bridging function of Tm(3+) ions in populating high-energy states of Eu(3+) ions.

Near vacuum ultraviolet luminescence of Gd3+ and Er3+ ions generated by super saturation upconversion processes

Near vacuum ultraviolet (UV) upconversion (UC) emissions with a spectral resolution of 1 nm, from the (6)G(J), (6)D(J), (6)I(J), (6)P(J) levels of Gd(3+) and the (2)L(17/2), (4)D(7/2), (2)H(2)(9/2), (2)D(5/2), (4)G(7/2), (2)K(13/2), (2)P(3/2) levels of Er(3+), were observed under 974 nm laser excitation. Mechanism analyses illustrate that successive energy transfers (ETs) from Yb(3+) to Er(3+) generate UV UC radiations in Er(3+), while two resonant ETs from Er(3+) to Gd(3+) lead to UV UC radiations in Gd(3+). Power dependence analyses indicate that the expected inefficient four- and five-photon processes have been switched into efficient two-photon processes due to a super saturation UC phenomenon that employs consecutive saturations at the intermediate states.

Field enhancement in metallic subwavelength aperture arrays probed by erbium upconversion luminescence

Upconversion luminescence from erbium ions placed in the near field of subwavelength aperture arrays is used to investigate field enhancement of incident near-infrared light in such nanostructures. We study field enhancement due to the excitation of both propagating and localized surface plasmon resonances in arrays of square and annular apertures in a Au film. The conversion of 1480 nm excitation light to 980 nm emission is shown to be enhanced up to a factor 450 through a subwavelength hole array. The effects of array periodicity and aperture size are investigated. It is shown that a Fano model can describe both far-field transmission and near-field intensity. The upconversion enhancement reveals the wavelength and linewidth of the surface plasmon modes that are responsible for extraordinary transmission in such arrays. Angle-dependent measurements on annular aperture arrays prove that the field enhancement due to localized resonances is independent of the incident angle. These experiments provide insight in the mechanisms responsible for extraordinary transmission and are important for applications that aim to exploit near-field enhancement in nanostructured metal films.

A rapid hydrothermal synthesis of rare earth oxide activated Y (OH)3 and Y2O3 nanotubes

One-dimensional single crystalline rare earth ion (Tm(3+), Tb(+3), and Eu(3+)) doped Y (OH)(3) nanotubes with inner diameters of 20-110 nm, outer diameters of 50-140 nm, and 1-5 microm in length were prepared for the first time by a rapid hydrothermal method within a short reaction period (5 min) at subcritical temperature (320 degrees C) and high pressure (about 40 MPa). A temperature dependent nanostructure evolution study was performed under rapid hydrothermal conditions and the effects of other processing parameters such as concentration of KOH and reaction time were found to be key parameters for the formation of highly anisotropic crystal structures of rare earth hydroxide nanotubes. Rare earth ion (Tm(3+), Tb(+3), and Eu(3+)) doped Y(2)O(3) nanotubes can be obtained after calcinations above 450 degrees C. The luminescent property of rare earth doped Y(2)O(3) nanotubes was also explored and compared with reference samples prepared via a conventional co-precipitation method.

pH sensor based on upconverting luminescent lanthanide nanorods

The pH sensor exploits the phenomenon of upconversion luminescence and is based on a hydrogel matrix containing (a) nanorods of the NaYF(4):Er,Yb type that can be excited with 980-nm laser light to give a green and red (dual) emission, and (b) a longwave absorbing pH probe that causes a pH-dependent inner filter effect.

Optical nanoheater based on the Yb3+-Er3+ co-doped nanoparticles

Yb(3+)-Er(3+) co-doped fluoride nanoparticles have been prepared. When pumped by 975 nm laser diode into absorption band of Yb(3+), the laser-induced temperature rise up to 800 degrees C has been detected in the nanoparticles by measuring the ratio of the intensities of the thermalised up-conversion luminescence bands (2)H(11/2)-->(4)I(15/2) and (4)S(3/2)-->(4)I(15/2) of Er(3+). These results show that a controlled optical heating of the nanoparticles and their surrounding nano-volumes can be realised, while the location and temperature rise of the nanoparticles and heated nano-volumes can be detected distantly by means of luminescence.

Synthesis, characterization, and in vivo targeted imaging of amine-functionalized rare-earth up-converting nanophosphors

Rare-earth up-converting nanophosphors (UCNPs) have great potential to become a new generation of biological luminescent labels, but their use has been limited by difficulties in obtaining water-soluble UCNPs bearing appropriate functional groups. To address this problem, we report herein a simple and efficient procedure for the preparation of amine-functionalized UCNPs by a modified hydrothermal microemulsion route assisted with 6-aminohexanoic acid. The amine content of the resultant UCNPs has been determined to be (9.5+/-0.8) x 10(-5) mol/g, which not only confers excellent dispersibility in aqueous solution, but also allows further conjugation with targeted molecules such as folic acid (FA) as a ligand. By means of the laser scanning up-conversion luminescence microscopy (LSUCLM) and the in vivo up-conversion luminescence (UCL) imaging under excitation at the CW infrared laser at 980 nm, FA-coupled UCNPs have been demonstrated to be effective in targeting folate-receptor overexpressing HeLa cells in vitro and HeLa tumor in vivo and ex vivo. These results indicated that our UCNPs could be used as whole-body targeted UCL imaging agents.

Immunolabeling and NIR-excited fluorescent imaging of HeLa cells by using NaYF(4):Yb,Er upconversion nanoparticles

Upconversion fluorescent nanoparticles can convert a longer wavelength radiation (e.g., near-infrared light) into a shorter wavelength fluorescence (e.g., visible light) and thus have emerged as a new class of fluorescent probes for biomedical imaging. Rare-earth doped beta-NaYF(4):Yb,Er upconversion nanoparticles (UCNPs) with strong UC fluorescence were synthesized in this work by using a solvothermal approach. The UCNPs were coated with a thin layer of SiO(2) to form core-shell nanoparticles via a typical Stober method, which were further modified with amino groups. After surface functionalization, the rabbit anti-CEA8 antibodies were covalently linked to the UCNPs to form the antibody-UCNP conjugates. The antibody-UCNP conjugates were used as fluorescent biolabels for the detection of carcinoembryonic antigen (CEA), a cancer biomarker expressed on the surface of HeLa cells. The successful conjugation of antibody to the UCNPs was found to lead to the specific attachment of the UCNPs onto the surface of the HeLa cells, which further resulted in the bright green UC fluorescence from the UCNP-labeled cells under 980 nm near-infrared (NIR) excitation and enabled the fluorescent imaging and detection of the HeLa cells. These results indicate that the amino-functionalized UCNPs can be used as fluorescent probes in cell immunolabeling and imaging. Because the UCNPs can be excited with a NIR light to exhibit strong visible fluorescence and the NIR light is safe to the body and can penetrate tissue as deep as several inches, our work suggests that, with proper cell-targeting or tumor-homing peptides or proteins conjugated, the NaYF(4):Yb,Er UCNPs can find potential applications in the in vivo imaging, detection, and diagnosis of cancers.

Non-blinking and photostable upconverted luminescence from single lanthanide-doped nanocrystals

The development of probes for single-molecule imaging has dramatically facilitated the study of individual molecules in cells and other complex environments. Single-molecule probes ideally exhibit good brightness, uninterrupted emission, resistance to photobleaching, and minimal spectral overlap with cellular autofluorescence. However, most single-molecule probes are imperfect in several of these aspects, and none have been shown to possess all of these characteristics. Here we show that individual lanthanide-doped upconverting nanoparticles (UCNPs)--specifically, hexagonal phase NaYF(4) (beta-NaYF(4)) nanocrystals with multiple Yb(3+) and Er(3+) dopants--emit bright anti-Stokes visible upconverted luminescence with exceptional photostability when excited by a 980-nm continuous wave laser. Individual UCNPs exhibit no on/off emission behavior, or "blinking," down to the millisecond timescale, and no loss of intensity following an hour of continuous excitation. Amphiphilic polymer coatings permit the transfer of hydrophobic UCNPs into water, resulting in individual water-soluble nanoparticles with undiminished photophysical characteristics. These UCNPs are endocytosed by cells and show strong upconverted luminescence, with no measurable anti-Stokes background autofluorescence, suggesting that UCNPs are ideally suited for single-molecule imaging experiments.

Highly sensitive and selective label-free optical detection of DNA hybridization based on photon upconverting nanoparticles

We report a label-free optical detection scheme for DNA hybridization using photon upconverting nanoparticles. On the basis of luminescence resonance energy transfer between a donor and an acceptor, the method is highly sensitive and can differentiate targets with single base variation. Photon upconverting nanoparticles were used as the donor and an intercalating dye as the acceptor. The sensor could differentiate the perfectly matched target from the single-base mismatched target. The detection limit of this sensor toward perfectly matched target was calculated to be 20 fmol, with no photobleaching. Oligonucleotide sensors of such design demonstrate high sensitivity and specificity without fluorophore labeling.

Observation of size dependence in multicolor upconversion in single Yb3+, Er3+ Codoped NaYF4 nanocrystals

In this Letter we report on the investigation of the upconversion emission of single NaYF(4) nanocrystals codoped with Yb(3+) and Er(3+). Single nanocrystals on a coverslip are excited with continuous wave laser light at 973 nm in a confocal setup and the upconversion fluorescence is analyzed with a spectrometer. With the help of an atomic force microscope the size of the nanocrystals is simultaneously determined. A strong size-dependence of the spectral properties of the upconversion signal of individual nanocrystals is observed. We attribute this to a differing number of available phonons in the individual crystals for multiphonon relaxation processes, depending on their size. We believe that this result provides a new strategy in the synthesis of upconversion nanoparticles with different spectral properties by changing only their size as it is well-known from the case of semiconductor quantum dots.

Multimodal-luminescence core-shell nanocomposites for targeted imaging of tumor cells

Uniform silica-coated NaYF(4): 20 mol % Yb, 2 mol % Er nanocomposites with good dispersibility, containing organic dye incorporated in the silica shell and folic acid conjugated on the surface of the shell, were prepared and characterized. The core-shell nanocomposites are 20-22 nm in size, water soluble, and buffer stable, with good photostability and biocompatibility. Folic acid (FA) offers a means of targeting human cells that greatly overexpress the folate receptor (FR). By the use of confocal microscopy and quantitative flow cytometry analysis, we demonstrate the receptor-mediated delivery of FA-conjugated nanocomposites targeting FR-positive cell lines, such as KB cells. The receptor-mediated targeting was confirmed by a comparison with the uptake of these nanocomposites in FR-negative cell lines, such as MCF-7. These results show that the silica-coated upconverting nanophosphor (UCNP) nanocomposites prepared by our strategy can potentially be useful as multimodal bioimaging agents.

Color-coded multilayer photopatterned microstructures using lanthanide (III) ion co-doped NaYF4 nanoparticles with upconversion luminescence for possible applications in security

We report a method for fabricating predefined photopatterns of upconversion nanophosphors using a chemical amplification reaction for direct writing of films with multilayer color-coded patterning for security applications. To photopattern the nanocrystal film we have synthesized rare-earth ion (Er(3+)/Yb(3+) or Tm(3+)/Yb(3+)) co-doped sodium yttrium fluoride (alpha-NaYF(4)) nanophosphors and functionalized the nanocrystal surfaces by incorporation of a photopatternable ligand such as t-butoxycarbonyl (t-BOC). The surface modification allows photopatterning of the nanophosphor solid state film. Furthermore, upconversion nanophosphors show a nearly quadratic dependence of the upconversion photoluminescence (PL) intensity on the excitation light power, and tailoring of the PL wavelength is possible by changing the lanthanide ions. We have demonstrated the capability of anchoring nanophosphors at desirable locations by a photolithography technique. The photopatterned films exhibit fixed nanophosphor structures clearly identifiable by strong upconversion photoluminescence under IR illumination which is useful for a number of applications in security.

Scanning thermal imaging by near-field fluorescence spectroscopy

A scanning thermal microscope that uses a fluorescent particle as a temperature probe has been developed. The particle, made of a rare-earth ion-doped fluoride glass, is glued at the extremity of a sharp tungsten tip and scanned on the surface of an electronic device. The temperature of the device is determined by measuring the fluorescence spectrum of the particle at every point on the surface and by comparing the intensity variations of two emission lines. As an example, we will show some images obtained on a nickel stripe 1 microm wide, heated by an electrical current. A good agreement is observed with a simulation of the temperature field on the device.

A bioaccumulative cyclometalated platinum(II) complex with two-photon-induced emission for live cell imaging

The cyclometalated platinum(II) complex [Pt(L)Cl], where HL is a new cyclometalating ligand 2-phenyl-6-(1H-pyrazol-3-yl)pyridine containing C(phenyl), N(pyridyl), and N(pyrazolyl) donor moieties, was found to possess two-photon-induced luminescent properties. The two-photon-absorption cross section of the complex in N,N-dimethylformamide at room temperature was measured to be 20.8 GM. Upon two-photon excitation at 730 nm from a Ti:sapphire laser, bright-green emission was observed. Besides its two-photon-induced luminescent properties, [Pt(L)Cl] was able to be rapidly accumulated in live HeLa and NIH3T3 cells. The two-photon-induced luminescence of the complex was retained after live cell internalization and can be observed by two-photon confocal microscopy. Its bioaccumulation properties enabled time-lapse imaging of the internalization process of the dye into living cells. Cytotoxicity of [Pt(L)Cl] to both tested cell lines was low, according to MTT assays, even at loadings as high as 20 times the dose concentration for imaging for 6 h.

Synthesis, Characterization and Biosensing Application of Photon Upconverting Nanoparticles

Phosphor/fluorescent molecules/particles have been widely used in various applications for quite some time. Typically, light with longer wavelength(s) is emitted when excited by shorter wavelength light. The opposite effect also exists, where a phosphor particle is excited with an infrared or red light and emits color(s) of shorter wavelengths, a process called up-conversion. Materials with upconverting properties have narrower absorption and line emission spectra than their down-converting counterparts. Because most non-target materials in a complex mixture do not possess such photon up-conversion properties, a dramatically improved S/N ratio is expected in sensing and luminescence reporting applications. This makes photon upconverting materials ideal for identification of trace amounts of target molecules. Here we report the synthesis, characterization and DNA detection application based on NaYF(4):Yb(3+), Er(3+) photon upconverting nanoparticles. The design of a nucleotide sensor for the detection of point mutation associated with sickle cell disease is described. The underlying principle for the detection is luminescence resonance energy transfer (LRET), with the photon upconverting nanoparticle as the donor and a dye, N,N,N',N'-tetramethyl-6-carboxyrhodamine (TAMRA), as the acceptor. The detection scheme is based on a sandwich-type hybridization format. The presence of the target DNA is indicated by the increase of the normalized acceptor's emission. Based on photon upconverting nanoparticles, which display high S/N ratio and no photobleaching, the DNA sensor demonstrates high sensitivity and specificity. The results demonstrate great potential of such nanomaterials as oligonucleotide sensors.

On-chip green silica upconversion microlaser

We demonstrate an erbium-doped silica toroidal microcavity upconversion laser on a silicon chip lasing in the visible spectral range (510-580 nm). The microcavity is pumped at 1458 nm by a tapered optical fiber coupled to the cavity and the lasing threshold is 690 muW. Lasing is observed at room temperature despite the high nonradiative relaxation rates of Er in pure silica that usually precludes upconversion lasing from higher excited states. This is attributed to the very high circulating pump power in the high-Q microcavity (Q>10(7)).

Cyclic RGD peptide-labeled upconversion nanophosphors for tumor cell-targeted imaging

One of the great challenges of oncology is to improve methods for early tumor detection. Thus tumor cell-targeted optical imaging has been intensively studied. Bioimaging with upconversion (UC) phosphors (UCPs) is of considerable interest due to a variety of possible applications taking advantage of infrared-to-visible luminescence. Here we report for the first time tumor cell-targeted UC imaging using UCPs modified with cyclic RGD peptide (RGD-Y2O3). Cyclic RGD peptide binds specifically to integrin alphavbeta3 which is highly expressed in a tumor cell surface of certain cancer types but not in normal tissues. Since UC emission from RGD-Y2O3 was observed for U87MG cancer cell (high integrin alphavbeta3 expression), but not for MCF-7 cancer cell (low integrin alphavbeta3 expression), this UC imaging is considered to be integrin alphavbeta3 specific. The non-invasive imaging of integrin alphavbeta3 expression using UCP-based probes will have great potential in cancer imaging in general in living subjects.

Lanthanide-containing light-emitting organic-inorganic hybrids: a bet on the future

Interest in lanthanide-containing organic-inorganic hybrids has grown considerably during the last decade, with the concomitant fabrication of materials with tunable attributes offering modulated properties. The potential of these materials relies on exploiting the synergy between the intrinsic characteristics of sol-gel derived hosts (highly controlled purity, versatile shaping and patterning, excellent optical quality, easy control of the refractive index, photosensitivity, encapsulation of large amounts of isolated emitting centers protected by the host) and the luminescence features of trivalent lanthanide ions (high luminescence quantum yield, narrow bandwidth, long-lived emission, large Stokes shifts, ligand-dependent luminescence sensitization). Promising applications may be envisaged, such as light-emitting devices, active waveguides in the visible and near-IR spectral regions, active coatings, and bio-medical actuators and sensors, opening up exciting directions in materials science and related technologies with significant implications in the integration, miniaturization, and multifunctionalization of devices. This review provides an overview of the latest advances in Ln(3+)-containing siloxane-based hybrids, with emphasis on the different possible synthetic strategies, photoluminescence features, empirical determination.

Synthesis of uniform rare earth fluoride (NaMF4) nanotubes by in situ ion exchange from their hydroxide [M(OH)3] parents

In this article, we demonstrate the production of uniform hexagonal sodium rare earth fluoride (beta-NaMF(4)) nanotubes through a hydrothermal in situ ion-exchange reaction by using rare earth hydroxides [M(OH)(3)] as a parent. The trivalent rare earth hydroxides were hydrothermally prepared at 120 degrees C and possessed a quasi-layered structure, which could be formed to be nanotubal morphology through a rolling up process from 2-D sheets. Moreover, the hexagonal structure of rare earth hydroxides [M(OH)(3)] displays a noticeable similarity with beta-NaMF(4). This similarity makes the formation of beta-NaMF(4) with nonlayered structure possible through in situ chemical transformation from M(OH)(3) with a layered structure. The single-crystal beta-NaMF(4) nanotubes were synthesized with well-controlled diameter (80-500 nm), aspect ratio (6-30), wall thickness (25-80 nm), and contents (such as M = Pr, Sm, Gd, Tb, Dy, Er, as well as lanthanide-doped rare earth NaMF(4)). The multicolor upconversion fluorescence has also been successfully realized in the Yb(3+)/Er(3+) (green) and Yb(3+)/Tm(3+) (blue) co-doped beta-NaMF(4) nanotubes by UC excitation in the NIR region. The various UC emission ratios of the samples were investigated as a function of hydrothermal reaction time to research the UC properties of the products and to further demonstrate the hydrothermal in situ ion-exchange process.

Nanofabricated upconversion nanoparticles for photodynamic therapy

We present a novel process for the production of three-layer Composite Nanoparticles (CNPs) in the size range 100-300 nm with an up-converting phosphor interior, a coating of porphyrin photosensitizer, and a biocompatible PEG outer layer to prevent clearance by the reticuloendothelial system. We show that these CNPs produce millimolar amounts of singlet oxygen at NIR intensities far less than other two-photon techniques.

Highly sensitive and selective oligonucleotide sensor for sickle cell disease gene using photon upconverting nanoparticles

We report the design of an oligonucleotide sensor for the detection of point mutation associated with sickle cell disease. The sensor was based on luminescence resonance energy transfer between a donor and an acceptor. Photon upconverting nanoparticles (NaYF(4) doped with Yb(3+) and Er(3+)) were used as the donor and a conventional fluorophore, N,N,N',N'-tetramethyl-6-carboxyrhodamine (TAMRA), as the acceptor. The sensor could detect the perfectly matched target, in the background of the mismatched target or other oligonucleotides of random sequences. The detection limit of this sensor towards perfectly matched target was calculated to be 120 femtomoles, with no photobleaching. Oligonucleotide sensors of such design demonstrate high sensitivity and specificity.