The Effect of Particle Morphology and Crystallite Size on the Upconversion Luminescence Properties of Erbium and Ytterbium Co-doped Yttrium Oxide Phosphors

Temperature sensing using bulk and nanoparticles of Ca0.79Er0.01Yb0.2MoO4 phosphor

Optical temperature sensing is widely realized by using upconversion (UC) emission in lanthanide-doped phosphors. There are so many various parameters that are responsible for UC intensity of the phosphor like particle shape and size, type of symmetry that exist at the site position, distribution of lanthanide ions in the phosphor, and so on. However, a comparative study of the bulk and nanostructure on the temperature sensing ability of such phosphor is rare. In the present work, we have taken Ca0.79Er0.01Yb0.2MoO4 phosphors as a model system and synthesized its bulk (via solid-state reaction method, named SCEY) and nanostructures (via solution combustion route, named CCEY). We further studied their phase, crystal structure, phonon frequency, optical excitation, and emission (upconversion & downshifting) properties. Finally, the optical temperature sensing behavior of SCEY and CCEY, in the range 305 K - 573 K, have been compared. The maximum relative sensitivity of the phosphor SCEY and CCEY are 0.0061 K-1 at 305 K and 0.0094 K-1 at 299 K, respectively, while, the maximum absolute sensitivities are 0.0150 K-1 at 348 K, and 0.0170 K-1 at 398 K, respectively. We thus conclude that the temperature sensing ability of nanoparticle-based Ca0.79Er0.01Yb0.2MoO4 phosphor is better compared to its bulk phosphor.

Versatile, stable, and air-tolerant triplet–triplet annihilation upconversion block copolymer micelles

A versatile, stable, and highly air-tolerant triplet–triplet annihilation up-conversion system based on block copolymer micelles was designed and fabricated.

Enhanced up-conversion emission in Er3+-doped barium–natrium–yttrium–fluoride phosphors by alkali ion introduction under 1550 nm excitation

This figure shows the emission spectra of nanocrystals with different Li+ ion introducing concentrations at 1550 nm. Compared with the untreated samples, when the Li+ ion introducing concentration is 0.2 mol%, the luminescence intensity of the sample is improved obviously.

Mechanism of upconversion luminescence enhancement in Yb3+/Er3+ co-doped Y2O3 through Li+ incorporation

Li⁺ doping is a well-known, simple, yet efficient strategy to optimize the properties of upconverting materials. Nonetheless, the position of Li⁺ in the lattice and the mechanism of upconversion enhancement are still controversial, especially in Yb³⁺/Er³⁺ co-doped Y₂O₃. This paper presents a comprehensive investigation of the above issues (i.e. the position occupied by Li⁺ in the lattice and the mechanism of luminescence enhancement, in terms of decreased defects) by studying (Y_0.78-XYb_0.20Er_0.02Li_X)₂O₃ powders. Neutron powder diffraction was employed for the first time in the literature to show that Li⁺ ions are accommodated in Y sites of YO₆ octahedra, confirmed also by the content of oxygen defects, which was increased with the increase of Li⁺ concentration. FT-IR showed that there was a small change in the amount and the type of the surface-absorbed groups with the increase in the Li⁺ content, thus not supporting the prevailing conclusion that the quenching groups are decreased by doping Li⁺. Positron annihilation lifetime (PLAS) experiments showed that the total defect concentration and the large defect clusters, which are considered as quenching centers, are decreased with increasing Li⁺-content, resulting in the enhancement of the emission intensity in Yb³⁺/Er³⁺ co-doped Y₂O₃.

Effect of Synthesis Techniques on the Optical Properties of Ho3+/Yb3+ Co-doped YVO4 Phosphor: A Comparative Study

The Ho³⁺/Yb³⁺-codoped YVO₄ phosphors have been synthesized by three different techniques (viz., solution combustion, sol-gel, and solid-state reaction techniques). X-ray diffraction patterns confirm the formation of a pure phase in the samples synthesized by all of the three methods; however, the average crystallite sizes in the three cases are different. The crystallite size increases if they are heated to higher temperature. The particle sizes are measured by scanning electron microscopy, which shows an increase in particle size with increasing the calcination temperature. The vibrational behavior of all of the three synthesized phosphor samples is studied by the Fourier transform infrared (FTIR) technique. The UV-vis absorption measurements give a large number of bands in all of the three samples prepared by three different methods. The upconversion (UC) emissions in all three samples have been monitored using a 980 nm diode laser. It gives an intense red emission in all of the three samples. Upconversion emission intensity is more prominent in the phosphor sample synthesized by the sol-gel technique and heated at 1473 K. The enhancement in UC emission intensity is well understood by the shape and size of the particles and also confirmed by the FTIR and UV-vis measurements. It is interesting to note that whereas UC measurements give red and weak green emissions, downshifting (DS) measurements show intense green, weak red, and broad blue emissions on UV excitation (323 nm). The DS behavior shows the same characteristics of the enhancement in overall emission. Overall, the phosphor sample synthesized by the sol-gel method gives better results in upconversion and downshifting behaviors when heated at 1473 K.

Strong up-conversion luminescence of rare-earth doped oxide films enhanced by gap modes on ZnO nanowires

Up-conversion luminescence (UCL) from rare-earth doped oxide (RE) films has great potential for application in fields such as solar cells, bioanalysis, or display technologies. However, the relatively high phonon energy of oxide matrices usually facilitates nonradiative relaxation leading to low UCL efficiency. Herein, we report a three-layer hierarchical structure of Ag/ZnO nanowires (nw-ZnO)/RE composite films, which enhances the UCL of rare-earth doped oxide films. An optimization of the geometric structure of the composite films demonstrated an increase of UCL by up to almost two orders of magnitude in Er³⁺ and Tm³⁺ doped YbMoO₄ films. This UCL enhancement is attributed to the formation of a very strong electric field in the tips of the nw-ZnO creating a highly effective electric field at the composite films, combined with reflection at the silver layer. Furthermore, we use the UCL properties of these novel Ag/nw-ZnO/RE composite films to demonstrate their possible use in ZnO-based photocatalytic processes to enhance the utilization of near-infrared sunlight in these devices.

Cathodoluminescence of Y2O3:Ln3+ (Ln = Tb, Er and Tm) and Y2O3:Bi3+ nanocrystalline particles at 200 keV

The cathodoluminescence (CL) spectra of nanocrystalline Y₂O₃:Tb³⁺ (0.3%), Y₂O₃:Er³⁺ (1%), Y₂O₃:Tm³⁺ (2%) and Y₂O₃:Bi³⁺ (1%) were recorded in a transmission electron microscope at 200 keV, low current density and various temperatures.

Slow Photons for Photocatalysis and Photovoltaics

Solar light is widely recognized as one of the most valuable renewable energy sources for the future. However, the development of solar-energy technologies is severely hindered by poor energy-conversion efficiencies due to low optical-absorption coefficients and low quantum-conversion yield of current-generation materials. Huge efforts have been devoted to investigating new strategies to improve the utilization of solar energy. Different chemical and physical strategies have been used to extend the spectral range or increase the conversion efficiency of materials, leading to very promising results. However, these methods have now begun to reach their limits. What is therefore the next big concept that could efficiently be used to enhance light harvesting? Despite its discovery many years ago, with the potential for becoming a powerful tool for enhanced light harvesting, the slow-photon effect, a manifestation of light-propagation control due to photonic structures, has largely been overlooked. This review presents theoretical as well as experimental progress on this effect, revealing that the photoreactivity of materials can be dramatically enhanced by exploiting slow photons. It is predicted that successful implementation of this strategy may open a very promising avenue for a broad spectrum of light-energy-conversion technologies.

Magneto-Photoluminescence Based on Two-Photon Excitation in Lanthanide-Doped Up-Conversion Crystal Particles

Experimental studies on magneto-photoluminescence based on two-photon excitation in up-conversion Y₂ O₂ S:Er, Yb crystal particles are reported. It is found that the up-conversion photoluminescence generated by two-photon excitation exhibits magnetic field effects at room temperature, leading to a two-photon excitation-induced magneto-photoluminescence, when the two-photon excitation exceeds the critical intensity. By considering the spin selection rule in electronic transitions, it is proposed that spin-antiparallel and spin-parallel transition dipoles with spin mixing are accountable for the observed magneto-photoluminescence. Specifically, the two-photon excitation generates spin-antiparallel electric dipoles between ⁴ S_3/2 -⁴ I_15/2 in Er³⁺ ions. The antiparallel spins are conserved by exchange interaction within dipoles. When the photoexcitation exceeds the critical intensity, the Coulomb screening can decrease the exchange interaction. Consequently, the spin-orbital coupling can partially convert the antiparallel dipoles into parallel dipoles, generating a spin mixing. Eventually, the populations between antiparallel and parallel dipoles reach an equilibrium established by the competition between exchange interaction and spin-orbital coupling. Applying a magnetic field can break the equilibrium by disturbing spin mixing through introducing spin precessions, changing the spin populations on antiparallel and parallel dipoles and leading to the magneto-photoluminescence. Therefore, spin-dependent transition dipoles present a convenient mechanism to realize magneto-photoluminescence in multiphoton up-conversion crystal particles.

Synthesis of Y2O3:Bi3+,Yb3+ nanosheets from layered yttrium hydroxide precursor and their photoluminescence properties

Morphologies, photoluminescence properties, and photostability were characterized for Y₂O₃:Bi³⁺,Yb³⁺ fluorescent nanosheets prepared through calcining solvothermally synthesized layered yttrium hydroxide precursors.

Targeted Nanoparticle Thermometry: A Method to Measure Local Temperature at the Nanoscale Point Where Water Vapor Nucleation Occurs

An optical nanothermometer technique based on laser trapping, moving and targeted attaching an erbium oxide nanoparticle cluster is developed to measure the local temperature. The authors apply this new nanoscale temperature measuring technique (limited by the size of the nanoparticles) to measure the temperature of vapor nucleation in water. Vapor nucleation is observed after superheating water above the boiling point for degassed and nondegassed water. The average nucleation temperature for water without gas is 560 K but this temperature is lowered by 100 K when gas is introduced into the water. The authors are able to measure the temperature inside the bubble during bubble formation and find that the temperature inside the bubble spikes to over 1000 K because the heat source (optically-heated nanorods) is no longer connected to liquid water and heat dissipation is greatly reduced.

Enhanced 2.7 μm mid-infrared emissions of Er3+ via Pr3+ deactivation and Yb3+ sensitization in LiNbO3 crystal

The use of Pr³⁺ codoping for enhancement of the transition of Er³⁺: ⁴I_11/2 → ⁴I_13/2 2.7 μm emissions was investigated in the Er/Yb codoped LiNbO₃ crystal for the first time. It is found that the codoped of Pr³⁺ ion in Er³⁺, Yb³⁺ and Pr³⁺ triply doped LiNbO₃ crystal (Er/Yb/Pr: LN) greatly enhances Er³⁺: 2.7 μm emission under excitation of a common 970 nm laser diode, depopulates the lower laser level of Er³⁺:⁴I_13/2, and has little influence on the higher laser level of Er³⁺:⁴I_11/2 at the same time for population inversion. The 2.7 μm emission characteristics and energy transfer were investigated in detail. The energy transition efficiency from lower laser level of Er³⁺:⁴I_13/2 to Pr³⁺:³F₄ level is as high as 0.42, indicating that the Pr³⁺ ion is an effective deactivation ion for Er³⁺ ion in LiNbO₃ crystal. These results suggest that Er/Yb/Pr: LiNbO₃ crystal may become an attractive host for developing solid state lasers at around 2.7 μm under a conventional 970 nm LD pump.

Photoluminescence properties of Eu3+ ions in yttrium oxide nanoparticles: defect vs. normal sites

The position of activator ions in the lattice has a fundamental effect on the luminescent properties of phosphors.

Investigation into optical heating and applicability of the thermal sensor bifunctional properties of Yb3+ sensitized Tm3+ doped Y2O3, YAG and LaAlO3 phosphors

Bifunctional properties of Yb³⁺ sensitized Tm³⁺ doped Y₂O₃, YAG and LaAlO₃ phosphors were investigated according to experimental and theoretical calculations.

Infrared-to-Visible Light Conversion in Er(3+) -Yb(3+) :Lu3 Ga5 O12 Nanogarnets

Er(3+) -Yb(3+) co-doped Lu3 Ga5 O12 nanogarnets were prepared and characterized; their structural and luminescence properties were determined as a function of the Yb(3+) concentration. The morphology of the nanogarnets was studied by HRTEM. Under 488 nm excitation, the nanogarnets emit green, red, and near-infrared light. The decay curves for the ((4) S3/2 , (2) H11/2 ) and (4) F9/2 levels of the Er(3+) ions exhibit a non-exponential nature under resonant laser excitation and their effective lifetimes are found to decrease with an increase in the Yb(3+) concentration from 1.0 to 10.0 mol %. The non-exponential decay curves are well fitted to the Inokuti-Hirayama model for S=8, indicating that the mechanism of interaction for energy transfer between the optically active ions is of dipole-quadrupole type. Upon 976 nm laser excitation, an intense green upconverted emission is clearly observed by the naked eyes. A significant enhancement of the red-to-green intensity ratio of Er(3+) ions was observed with an increase in Yb(3+) concentration. The power dependence and the dynamics of the upconverted emission confirm the existence of two-photon upconversion processes for the green and red emissions.

Luminescence studies and infrared emission of erbium-doped calcium zirconate phosphor

The near-infrared-to-visible upconversion luminescence behaviour of Er(3+)-doped CaZrO3 phosphor is discussed in this manuscript. The phosphor was prepared by a combustion synthesis technique that is suitable for less-time-taking techniques for nanophosphors. The starting materials used for sample preparation were Ca(NO3)2.4H2O, Zr(NO3)4 and Er(NO3)2, and urea was used as a fuel. The prepared sample was characterized by X-ray diffraction (XRD). The surface morphology of prepared phosphor was determined by field emission gun scanning electron microscopy (FEGSEM). The functional group analysis was determined by Fourier transform infrared (FTIR) spectroscopy. All prepared phosphors with variable Er(3+) concentrations (0.5-2.5 mol%) were studied by photoluminescence analysis. It was found that the excitation spectra of the prepared phosphor showed a sharp excitation peak centred at 980 nm. The emission spectra with variable Er(3+) concentrations showed strong peaks in the 555 nm and 567 nm range, with a dominant peak at 555 nm due to the ((2)H(11/2),(4)S(3/2)) transition and a weaker transition at 567 nm associated with 527 nm. Spectrophotometric determination of the peak was evaluated by the Commission Internationale de I'Eclairage (CIE) method These upconverted emissions were attributed to a two-photon process. The excitation wavelength dependence of the upconverted luminescence, together with its time evolution after infrared pulsed excitation, suggested that energy transfer upconversion processes were responsible for the upconversion luminescence. The upconversion mechanisms were studied in detail through laser power dependence. Excited state absorption and energy transfer processes were discussed as possible upconversion mechanisms. The cross-relaxation process in Er(3+) was also investigated.

An up-converting HAP@β-TCP nanocomposite activated with Er3+/Yb3+ ion pairs for bio-related applications

A HAP@β-TCP nanocomposite doped with Er³⁺/Yb³⁺ ions was prepared and its cytotoxicity was tested on canine osteosarcoma and murine macrophage cells. Metronidazole release from the nanocomposite was studied and its up-conversion properties measured.

Investigation into the temperature sensing behavior of Yb3+ sensitized Er3+ doped Y2O3, YAG and LaAlO3 phosphors

The sensitivities (S) of Y₂O₃ (YAG/LaAlO₃):Yb³⁺/Er³⁺ phosphors increased with increasing average bond covalency and the calculated values were basically in good agreement with our experimental results.

Upconverting nanoparticles: assessing the toxicity

Based on a survey of existing studies, low nanotoxicity of lanthanide doped upconverting nanoparticles holds promise for their safety and suitability for biomedical detection and imaging.

Lanthanide-doped upconversion materials: emerging applications for photovoltaics and photocatalysis

Photovoltaics and photocatalysis are two significant applications of clean and sustainable solar energy, albeit constrained by their inability to harvest the infrared spectrum of solar radiation. Lanthanide-doped materials are particularly promising in this regard, with tunable absorption in the infrared region and the ability to convert the long-wavelength excitation into shorter-wavelength light output through an upconversion process. In this review, we highlight the emerging applications of lanthanide-doped upconversion materials in the areas of photovoltaics and photocatalysis. We attempt to elucidate the fundamental physical principles that govern the energy conversion by the upconversion materials. In addition, we intend to draw attention to recent technologies in upconversion nanomaterials integrated with photovoltaic and photocatalytic devices. This review also provides a useful guide to materials synthesis and optoelectronic device fabrication based on lanthanide-doped upconversion materials.

Surface-directed synthesis of erbium-doped yttrium oxide nanoparticles within organosilane zeptoliter containers

We introduce an approach to synthesize rare earth oxide nanoparticles using high temperature without aggregation of the nanoparticles. The dispersity of the nanoparticles is controlled at the nanoscale by using small organosilane molds as reaction containers. Zeptoliter reaction vessels prepared from organosilane self-assembled monolayers (SAMs) were used for the surface-directed synthesis of rare earth oxide (REO) nanoparticles. Nanopores of octadecyltrichlorosilane were prepared on Si(111) using particle lithography with immersion steps. The nanopores were filled with a precursor solution of erbium and yttrium salts to confine the crystallization step to occur within individual zeptoliter-sized organosilane reaction vessels. Areas between the nanopores were separated by a matrix film of octadecyltrichlorosilane. With heating, the organosilane template was removed by calcination to generate a surface array of erbium-doped yttria nanoparticles. Nanoparticles synthesized by the surface-directed approach retain the periodic arrangement of the nanopores formed from mesoparticle masks. While bulk rare earth oxides can be readily prepared by solid state methods at high temperature (>900 °C), approaches for preparing REO nanoparticles are limited. Conventional wet chemistry methods are limited to low temperatures according to the boiling points of the solvents used for synthesis. To achieve crystallinity of REO nanoparticles requires steps for high-temperature processing of samples, which can cause self-aggregation and dispersity in sample diameters. The facile steps for particle lithography address the problems of aggregation and the requirement for high-temperature synthesis.

Novel Cu₂O quantum dots coupled flower-like BiOBr for enhanced photocatalytic degradation of organic contaminant

Here we report a highly efficient novel photocatalyst consisting of Cu2O quantum dots (QDs) incorporated into three-dimensional (3D) flower-like hierarchical BiOBr (hereafter designated QDs-Cu2O/BiOBr), which were synthesized via a simple reductive solution chemistry route and applied to decontaminate the hazardous wastewater containing phenol and organic dyes. The deposition of Cu2O QDs onto the surface of the BiOBr was confirmed by structure and composition characterizations. The QDs-Cu2O/BiOBr composites exhibited superior activity for organic contaminant degradation under visible light and 3 wt% QDs-Cu2O/BiOBr composite showed the highest degrade rate for phenol and methylene blue (MB), which was 11.8 times and 1.4 times than that of pure BiOBr, indicated the QDs-Cu2O/BiOBr composite has the great potential application in purifying hazardous organic contaminant. The incorporated Cu2O QDs played an important role in improving the photocatalytic performance, due to the enhancement of visible light absorption efficiency as well as the efficient separation of the photogenerated charge carriers originating from the intimately contacted interface and the well-aligned band-structures, which was confirmed by the results of PL, photocurrent and EIS measurements. The possible photocatalytic mechanism was proposed based on the experiments and theoretical results.

Concentration dependence of the up- and down-conversion emission colours of Er(3+)-doped Y2O3: a time-resolved spectroscopy analysis

In this paper, a series of Er(3+)-doped Y2O3 samples are systematically investigated, focusing on the effect of the doping concentration on the emission lifetime and spectrum under both 488 nm and 980 nm excitations. Decay times of the (4)S3/2 and (4)F9/2 emitting states under 488 nm and 980 nm excitations are found to be different and concentration dependent. We explain these variations in terms of the changes in the up-conversion routes caused by the predominance of energy exchanges that involve the lowest lying excited states.

Structural and optical properties of Er3+/Yb3+ doped barium titanate phosphor prepared by co-precipitation method

In the present work we have synthesized the Er(3+)/Yb(3+) codoped barium titanate phosphor via co-precipitation method and studied its upconversion emission properties. The prepared BaTiO3 powder was found in cubic phase as a major component and having good crystallinity revealed by the XRD analysis. Optical band gap of the cubic barium titanate was calculated using the diffuse reflectance absorption spectrum. Good green upconversion emission is observed from the samples when excited by 980 nm diode laser. The variation in upconversion emission intensity is studied with the increase in excitation power as well as temperature of the sample. It is found that the emission bands centred at 524 and 548 nm are thermally coupled and can act as a temperature sensor in the 300-480 K temperature range.

Bilayer stabilized Ln3+-doped CaMoO4 nanocrystals with high luminescence quantum efficiency and photocatalytic properties

In this article, we discuss the microwave synthesis of sodium dodecyl sulphate (SDS) stabilized Ln³⁺-doped CaMoO₄ nanocrystals (Ln³⁺ = Eu³⁺, Er³⁺/Yb³⁺).

Color-tunable up-conversion emission in Y2O3:Yb3+, Er3+ nanoparticles prepared by polymer complex solution method

Powders of Y2O3 co-doped with Yb3+ and Er3+ composed of well-crystallized nanoparticles (30 to 50 nm in diameter) with no adsorbed ligand species on their surface are prepared by polymer complex solution method. These powders exhibit up-conversion emission upon 978-nm excitation with a color that can be tuned from green to red by changing the Yb3+/Er3+ concentration ratio. The mechanism underlying up-conversion color changes is presented along with material structural and optical properties. PACS: 42.70.-a, 78.55.Hx, 78.60.-b.

Structure, enhancement and white luminescence of multifunctional Lu₆O₅F₈:20%Yb³⁺,1%Er³⁺(Tm³⁺) nanoparticles via further doping with Li⁺ under different excitation sources

A series of Lu6O5F8:20%Yb(3+),1%Er(3+)(Tm(3+)),x%Li(+) (0 ≤ x ≤ 12) nanoparticles with average size from 20 to 320 nm upon increasing Li(+) concentration were prepared by a coprecipitation method. The detailed crystal structure of Lu6O5F8 as a new matrix is firstly analysed via retrieved refinement of the powder X-ray diffraction (XRD). In addition, the corresponding Powder Diffraction File card information was also obtained through indexing the XRD pattern of the host. Upconversion under excitation at 980 nm, downconversion with Xe lamp as excitation source and cathodoluminescence properties of Lu6O5F8:20%Yb(3+),1%Er(3+)(Tm(3+)),x%Li(+) (0 ≤ x ≤ 12) nanoparticles were compared and studied. It is worthwhile pointing out that according to the effects of Li(+) on emission intensity ratio, white UC emission was achieved in the Lu6O5F8:6%Yb(3+),0.3%Er(3+),0.4%Tm(3+),5%Li(+) compared to Li(+) free sample with the same activator concentration. The reasons behind this behavior were presented and discussed. All in all, Li(+) ion would be a wonderful luminescence intensifier for lanthanide ions, and the multifunctional lanthanide ion-doped Lu6O5F8 nanoparticles have potential application in photoluminescence areas and field emission display devices.

Contrasting behaviour of the co-activators in the luminescence spectra of Y2O2S:Tb3+,Er3+ nanometre sized particles under UV and red light excitation

Nanometre sized particles of terbium and erbium co-doped yttrium oxysulfide up-converting phosphors were prepared by a urea homogeneous-precipitation method. Results from X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) and photoluminescence spectroscopy studies on the microstructure and luminescent properties of the materials are reported. Upconversion emission was observed from the Er(3+) cations when particles were excited with laser light of 632.8 nm wavelength. Under these conditions no interactions between the Er(3+) cations and the Tb(3+) cations were observed. In contrast there was evidence from the Stokes emission of the Er(3+) cations under 254 nm excitation for an interaction between the Er(3+) and Tb(3+) cations reducing intensity of the latter's blue and green emission bands by cross relaxation processes.

Upconversion Luminescence Property of Nanocrystalline Y2O3:Pr3+,Yb 3+

The upconversion luminescence nanocrystalline powders Y2O3:Pr3+,Yb3+were prepared by co-precipitation method and characterized by X－ray diffraction,fluorescence spectrum and so on. Its luminescence property and the effect of different calcining temperatures and rare-earth ion doped concentration on its luminescence property were discussed. The results show that the nanocrystalline powders calcined at 800-1200 °C for 2h has a single crystalline phase -the solid solution cubic system phase of Y2O3. There is a upconversion luminescence phenomenon in the powders doped 1%(mol percent) Pr3+. The powders excited by a 980 nm laser diode emit weak green fluorescent observed by naked eye. The upconversion luminescence of Pr3+in Y2O3:Pr3+,Yb3+is obviously different that of Pr3+in other materials.There are two stronger emission zone in upconversion emission spectra of the powders in the 400nm-800nm range,whose center wavelength value are respectively 551nm, 762nm.Increasing the calcining temperature of the samples from 1000°C to 1200°C, the emission peak intensity sharply elevates.

Tuning of the structure and emission spectra of upconversion nanocrystals by alkali ion doping

Recently, lanthanide based nanocrystals with upconversion fluorescence emission have attracted a lot of interest and the nanocrystals have been used for bioimaging, biodetection, and therapeutic applications. Use of the nanocrystals for multiplexed detection has also been explored; however, nanocrystals with multicolor emission are required. Some efforts have been made to tune the emission spectra of the nanocrystals based on manipulation of upconverting lanthanide ions doped in the crystals or creation of core/shell structures. In this work, alkali ions with an ionic radius slightly larger or smaller than Na such as Li and K were doped into NaYF(4):Yb,Er nanocrystals and their effect on the crystal structure and subsequently the upconversion emission spectra were studied. It was found that the phase transition occurs in the nanocrystals when a different amount of Li and K was doped. Furthermore, the intensity ratios between the blue, green, and red emission peaks changed accordingly, and make it possible to tune the upconversion fluorescence of the nanocrystals by Li and K doping.

Synthesis of erbium oxide nanosheets and up-conversion properties

A novel erbium-based compound as well as Er(2)O(3) nanosheets have been synthesized through a simple hydrothermal route. The nanosheets are of 200 nm width and 10-15 nm thickness. It is suggested that this erbium-based compound has a possible formula of Er(2)O(5)H(4) with a primitive tetragonal structure (cell parameters: a = 8.465(1) and c = 15.117(2) Å). Face-centered cubic and body-centered cubic structured Er(2)O(3) nanosheets were obtained after calcination of this compound at 623 and 973 K, respectively, both having a paramagnetic behavior. Er(2)O(5)H(4) and Er(2)O(3) nanosheets have similar up-conversion properties with strong blue emission, which is rarely reported in the literature. The existence of absorbed surface contaminations in nanosheets might be the origin for the blue emission enhancement.

In vivo near-infrared fluorescence imaging of cancer with nanoparticle-based probes

The use of in vivo near-infrared fluorescence (NIRF) imaging techniques for sensitive cancer early detection is highly desirable, because biological tissues show very low absorption and autofluorescence in the NIR spectrum window. Cancer NIRF molecular imaging relies greatly on stable, highly specific and sensitive molecular probes. Nanoparticle-based NIRF probes have overcome some of the limitations of the conventional NIRF organic dyes, such as poor hydrophilicity and photostability, low quantum yield, insufficient stability in biological system, low detection sensitivity, etc. Therefore, a lot of efforts have been made to actively develop novel NIRF nanoparticles for in vivo cancer molecular imaging. The main focus of this article is to provide a brief overview of the synthesis, surface modification, and in vivo cancer imaging applications of nanoparticle-based NIRF probes, including dye-containing nanoparticles, NIRF quantum dots, and upconversion nanoparticles.