Visible Upconversion Luminescence Research Articles

Highly improved upconversion luminescence in NaGd(WO₄)₂:Yb³⁺/Tm³⁺ inverse opal photonic crystals.

The upconversion luminescence (UCL) of rare earth (RE) ions doped nanomaterials has attracted extensive interest because of its wide and great potential applications. However, the lower UCL efficiency is still an obstacle for real applications. Photonic modulation is a novel way to improve the efficiency of UCL. In this work, NaGd(WO4)2:Yb(3+)/Tm(3+) inverse opal photonic crystals (IOPCs) were fabricated through the polymethylmethacrylate (PMMA) template and the modification of the IOPC structure on the emission spectra and dynamics of Tm(3+) ions was systemically studied. It is interesting to observe that in the IOPCs, the high-order UCL (1)D2-(3)H6/(3)F4 was relatively enhanced. At the same time, the local thermal effect induced by laser irradiation was suppressed. Furthermore, the overall intensity ratio of visible UCL to near-infrared (NIR) down-conversion luminescence (DCL) was 2.8-8 times improved than that of the grinded reference (REF) and independent of the photonic stop band (PSB). The studies on UCL dynamics indicated that the nonradiative transition rate of Tm(3+) was considerably suppressed. The facts above indicated that in the IOPCs the UCL efficiency of Tm(3+) was largely improved due to the periodic macroporous structure.

Er3+ loaded barium molybdate nanoparticles: IR to visible spectral upconversion

In this study, we report the infrared to visible upconversion luminescence behavior of Er3+ loaded barium molybdate nanoparticles synthesized by microwave induced sol–gel route. Structural and morphological properties were analyzed and the upconversion response of the Er3+ loaded samples (1mol% and 5mol%) was investigated by exciting the samples at 980nm from a Continuous Wave Laser Diode (CWLD). Results showed that the green emissions around 528 and 546 and red emissions at 658nm were observed, respectively, and the intensity of both emissions were found to be enhanced with increase in concentration from 1mol% to 5mol% of Er3+ ions. Upconversion mechanism is disscussed and this study gives the way to convert infrared energy to visible light in other molybdate scheelite structures.

Effect of Yb3+ concentration on photoluminescence properties of cubic Gd2O3 phosphor

Yb3+ doped phosphor of Gd2O3 (Gd2O3:Yb3+) have been prepared by solid state reaction method. The structure and the particle size have been determined by X-ray powder diffraction measurements. The average particle size of the phosphor is in between 35 and 50nm. The particle size and structure of the phosphor was further confirmed by TEM analysis. The visible and NIR luminescence spectra were recorded under the 980nm laser excitation. The visible upconversion luminescence of Yb3+ ion was due to cooperative luminescence and the presence of rare earth impurity ions. The cooperative upconversion and NIR luminescence spectra as a function of Yb3+ ion concentration were measured and the emission intensity variation with Yb3+ ion concentration was discussed. Yb3+ energy migration quenched the cooperative luminescence of Gd2O3:Yb3+ phosphor with doping level over 5%, while the NIR emission luminescence continuously increases with increasing Yb3+ ion concentration.

Influence of Er(3+) concentration on the photoluminescence characteristics and excitation mechanism of Gd2O3:Er(3+) phosphor synthesized via a solid-state reaction method.

An Er(3+) -doped phosphor of Gd2O3(Gd2O3:Er(3+)) was prepared using a conventional solid-state reaction method. The structure and particle size were determined from X-ray powder diffraction measurements. The average particle size of the phosphor was in between 20 and 50 nm. The particle size and structure of the phosphor were further confirmed by transmission electron microscopy (TEM) analysis. Luminescence spectra were recorded under excitation wavelengths of 275, 380, 515 and 980 nm. The visible upconversion and downconversion luminescence spectra of the Gd2O3:Er(3+) phosphor were investigated as a function of Er(3+) ion concentration. The upconverted emission at 980 nm excitation shows enhanced red emission with respect to green emission as the dopant concentration increased. Similar results were observed for downconversion emission under 275 and 380 nm excitation wavelengths. The mechanisms responsible for populating the (4)S3/2 and (4)F9/2 levels, for green and red emissions, respectively, are different for different excitations and for different concentrations of Er(3+).

Near-infrared-light mediated ratiometric luminescent sensor for multimode visualized assays of explosives.

The development of a portable and easy-to-use device for the detection of explosives with high sensitivity and selectivity is in high demand for homeland security and public safety. In this study, we demonstrate miniaturized devices depending on the upconversion ratiometric luminescent probe for point-of-care (POC) assay of explosives with the naked-eye. When the PEI-coated upconversion nanoparticles (UCNPs) selectively bonded to 2,4,6-trinitrotoluene (TNT) explosives by the formation of Meisenheimer complex, the formed of UCNP-Meisenheimer complexes show turned visible multicolor upconversion luminescence (UCL) on account of TNT-modulating Förster resonance energy transfer process under near-infrared excitation. With UCL emission at 808 nm as internal standard and ratiometric UCL at 477 nm to that at 808 nm (I477/I808) as output signal, the probe can simultaneously meet the accuracy for TNT explosives quantitative analysis. In addition, this easy-to-use visual technique provides a powerful tool for convenient POC assay of rapid explosives identification.

Optical characterization, infrared emission and visible up-conversion in Er3 + doped tellurite glasses

In this work, Er3+ doped tellurite glasses have been prepared with the composition (82.5-x) TeO2+4.5Bi2O3+11.5ZnO+1.5Nb2O5+x Er2O3 (x=0.1, 0.3, 0.5, 0.7, 1.0mol%) by melt-quenching method and their physical, spectroscopic properties were investigated. The experimental oscillator strengths (fexp) of individual absorption peaks are used to estimate the Judd–Ofelt intensity parameters (Ωλ, λ=2, 4, 6). Judd–Ofelt intensity parameters are used to calculate the spontaneous transition probabilities, radiative lifetimes and branching ratios for certain excited states of Er3+ ions. NIR emission and visible up-conversion luminescence were observed at room temperature for all glasses by exciting with 980nm laser radiation. The emission characteristics such as peak stimulated emission cross section, FWHM, figure of merit, optical gain cross sections and measured lifetimes have been obtained for the observed Er3+: 4I13/2→4I15/2 transition in the above glass composition for all the concentrations and are compared with that of the reported. Finally, NIR to visible energy conversion has been analyzed for all glasses excited at 980nm and suitable mechanism was proposed.

Understanding the infrared to visible upconversion luminescence properties of Er3+/Yb3+ co-doped BaMoO4 nanocrystals

In this paper we report the infrared to visible upconversion luminescence properties of Er3+/Yb3+ co-doped BaMoO4 nanocrystals synthesized via microwave assisted sol–gel processing route. Structural, morphological and upconversion luminescence properties were investigated by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and Upconversion Photoluminescence spectra analysis. Results revealed that the oval shaped BaMoO4 nanocrystals ranging in size from 40 to 60nm having tetragonal scheelite crystal structure were obtained by sol–gel route. The infrared to visible upconversion luminescence has been investigated in Er3+/Yb3+ co-doped in BaMoO4with different Yb3+ concentrations. Intense green upconversion emissions around 528, 550nm, and red emission at 657nm corresponding to the 2H11/2, 4S3/2, and 4F9/2 transitions, respectively to the 4I15/2 ground state were observed when excited by CW laser radiation at 980nm. The green emissions were greatly enhanced after the addition of sensitizer (Yb3+ ions). The effect of Yb3+ on the upconversion luminescence intensity was analyzed and explained in terms of the energy transfer process based. The reported work establishes the understanding of molybdates as an alternative host material for upconversion luminescence.

Near infrared to visible upconversion emission in Er3+/Yb3+ co-doped NaGd(WO4)2 nanoparticles obtained by hydrothermal method

The Er3+/Yb3+ co-doped NaGd(WO4)2 nanoparticles have been prepared by a simply hydrothermal synthesis procedure. The crystal structures and morphologies of the products were characterized by XRD, SEM and FT-IR spectroscopy. The average grain size of these samples depended on the annealing temperature, increasing with the increase of the temperature. The intense visible upconversion and near infrared luminescence of the Er3+/Yb3+ co-doped NaGd(WO4)2 nanoparticles under 975nm excitation could be observed. The luminescence intensities of the samples depended on the size of the nanoparticles and Yb3+ concentration. The transition mechanisms of the upconversion emission can be ascribed to a two-photon absorption process.

Calcination-free micropatterning of rare-earth-ion-doped nanoparticle films on wettability-patterned surfaces of plastic sheets

We demonstrate a patterning technique of rare-earth-ion-doped (RE) nanoparticle films directly on wettability-patterned surfaces fabricated on plastic sheets in one step. Self-assembled monolayers consisting of silane-coupling agent with hydrophobic groups were fabricated on plastic sheets. UV–ozone treatments were performed through a metal mask to selectively remove the self-assembled monolayers in a patterned manner, resulting in the formation of wettability-patterned surfaces on plastic sheets. Using a water dispersion of Er3+ and Yb3+-codoped Y2O3 nanoparticles at a diameter of 100nm, RE-nanoparticle films were fabricated on the wettability-patterned surfaces by a dip-coating technique. By adjusting the concentration of RE-nanoparticle dispersion, withdrawal speed, and withdrawal angle, amount of RE-nanoparticles, we were able to control the structures of the RE-nanoparticle films. Fluorescence microscope observations demonstrate that visible upconversion luminescence and near-infrared fluorescence were emitted from the RE-nanoparticle films on the wettability-patterned surfaces. This technique allows for the fabrication of flexible emitting devices with long-operating life time with minimized material consumption and few fabrication steps, and for the application to sensors, emitting devices, and displays in electronics, photonics, and bionics in the future.

Two-Color Surface Plasmon Polariton Enhanced Upconversion in NaYF4:Yb:Tm Nanoparticles on Au Nanopillar Arrays

Spectroscopic imaging and time-resolved spectroscopy are used to study the surface plasmon polariton (SPP) enhanced infrared to visible upconversion luminescence from NaYF4:Tm:Yb nanoparticles embedded in polymethyl methylacrylate (PMMA) supported on Au nanopillar arrays. The arrays have a lattice resonance associated with the SPP near 980 nm, near-resonant with the peak absorption of the Yb3+ ion, while a local surface plasmon resonance (LSPR) associated with the individual pillars is seen to enhance the near-infrared emission of Tm3+ ions near 780 nm. The two combined channels of enhancement result in a significantly higher enhancement of the near-infrared emission when compared to the visible upconversion lines of the Tm3+ ion, consistent with the interpretation of sequential surface plasmon assisted absorption and emission at two separate and disparate energies. The presence of SPP and LSPR was confirmed by spectrally resolved reflectivity, and the mechanisms for luminescence enhancement were further ...

Efficient visible upconversion luminescence in Er3+ and Er3+/Yb3+ co-doped Y2O3 phosphors obtained by solution combustion reaction

Combustion derived Er3+ -doped Y2O3 and Er3+/Yb3+co-doped Y2O3 powders have been characterized by X-ray diffraction, energy dispersive X-ray analysis, Fourier transform infrared spectroscopy and laser excited spectroscopy. Formation of Y2O3 phosphor was confirmed by X-ray diffraction and energy dispersive X-ray analysis. The vibrational properties of Y2O3 powder was studied by Fourier transform infrared spectroscopy. The luminescence spectra of Er3+ -doped and Er3+/Yb3+ co-doped Y2O3 powders were studied under 379nm excitation. The strong up-conversion luminescence for Er3+ -doped and Er3+/Yb3+ co-doped Y2O3 powders have been observed under 978nm laser excitation. The effect of Yb3+ addition on optical and luminescence properties of Er3+:Y2O3 powders were studied. The ratio of red to green intensity has been enhanced when Er3+ -doped Y2O3 is co-doped with Yb3+ ions. The effect of co-doping of Yb3+ ions on the visible luminescence intensity of Er3+ has been studied and the mechanism responsible for the variation in the green and red intensity is discussed.

Phonon-modulated upconversion luminescence properties in some Er3+ and Yb3+ co-activated oxides

The competition between 4I13/2–4I15/2 near-infrared downconversion emissions and visible upconversion emissions of 2H11/2/4S3/2/4F9/2–4I15/2 is a vital factor for obtaining efficient upconversion luminescence (UCL) in Er3+ and Yb3+ co-activated oxides. In this paper, we systemically studied the entire emission spectra of Er3+ ranging from 400–1700 nm in Er3+ and Yb3+ co-activated cubic Y2O3, tetragonal GdVO4 and tetragonal NaGd(WO4)2 micro-sized powders, prepared by the same sol–gel method, which have different phonon thresholds, 600 cm−1, 880 cm−1 and 1000 cm−1, respectively. It is interesting to observe that in these phosphors, the visible UCL of Er3+ relative to near-infrared emissions increase remarkably with the increase of phonon thresholds. In comparison with the UCL in the Y2O3 host, the UCL in YVO4 and tetragonal NaGd(WO4)2 was tremendously improved by 9.5- and 120-fold, respectively. The UCL intensity of the NaGd(WO4)2:Yb3+/Er3+ was comparable to that of the famous UCP NaYF4:Yb3+/Er3+. A model was proposed to explain the phonon-modulated UC process. This work is of great significance in the search for a novel, efficient UCP.

Upconversion luminescence nanosensor for TNT selective and label-free quantification in the mixture of nitroaromatic explosives

This paper reports a rapid, sensitive, and selective nanosensor for the detection of 2,4,6-trinitrotoluene (TNT) in the mixture aqueous solution of nitroaromatics independent of immunoassay or molecularly imprinted technology and complicated instruments. Despite many strategies including immunoassay and molecularly imprinted technologies been successfully developed for the detection of TNT, it is not easy to differentiate TNT from 2,4,6-trinitrophenol (TNP) due to their very similar chemical structures and properties. In this work, the amine functionalized NaYF4:Yb(3+)/Er(3+) upconversion luminescence nanoparticles (UCNPs) whose excitation (980 nm) and emission (543 nm) wavelength were far from the absorbance bands of other usual interference nitroaromatics including 2,4-dinitrotoluene (DNT), nitrobenzene (NB), and especially TNP, were utilized as the luminescent nanosensors for TNT luminescence detection. To make these UCNPs highly water stable and render the charge transfer from UCNPs to TNT easier, amino groups were introduced onto the surface of the UCNPs by coating a polymer layer of ethylene glycol dimethacrylate (EGDMA) hybridized with 3-aminopropyltriethoxysilane (APTS). After binding with TNT through amino groups on the UCNPs, the naked eye visible green upconversion luminescence of the UCNPs was dramatically quenched and thus a sensitive UC luminescence nanosensor was developed for TNT detection. However, other nitroaromatics including TNP, DNT, and NB have no influence on the green UC luminescence and thus no influence on the TNT detection. The luminescence intensity is negatively proportional to the concentration of TNT in the range of 0.01-9.0 µg/mL with the 3σ limit of detection (LOD) of 9.7 ng/mL. The present studies provide a novel and facile strategy to fabricate the upconversion luminescence sensors with highly selective recognition ability in aqueous media and are desirable for label free analysis of TNT in mixed solution independent of immunoassay and molecularly imprinted technology and complicated instruments.

Enhancement of crystallisability and visible upconversion luminescence in SiO2–Al2O3–ZnF2–SrF2:Er3+/Li+ glass ceramic

Er3+/Li+ codoped SiO2–Al2O3–ZnF2–SrF2 glass ceramics were prepared, and infrared to visible upconversion emissions were observed under 1540 nm excitation. The 410, 524, 549 and 667 nm upconversion emissions correspond to the transitions 2H9/2→4I15/2, 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 respectively. The doping Li+ ions can not only significantly increase the crystallisability but also efficiently enhance the upconversion emission intensities. At the concentration of 1·5 mol.-%Li+, the green and red emission intensities can be increased by >10 times. The dependence of upconversion intensities on excitation power shows that the 524, 549 and 667 nm emissions take place via three-photon process, and the 410 nm emission occurs via four-photon process. The possible upconversion mechanisms are proposed based on the spectra and the excitation power dependence analyses.

Er3+/Yb3+co-doped bismuth molybdate nanosheets upconversion photocatalyst with enhanced photocatalytic activity

In this paper, we report the microwave hydrothermal synthesis of Er3+/Yb3+ co-doped Bi2MoO6 upconversion photocatalyst. Crystal structure, morphology, elemental composition, optical properties and BET surface area were analyzed in detail. Infrared to visible upconversion luminescence at 532nm and 546nm of the co-doped samples was investigated under excitation at 980nm. The results revealed that the co-doping of Er3+/Yb3+ into Bi2MoO6 exhibited enhanced photocatalytic activity for the decomposition of rhodamine B under simulated solar light irradiation. Enhanced photocatalytic activity can be attributed to the energy transfer between Er3+/Yb3+ and Bi2MoO6 via infrared to visible upconversion from Er3+/Yb3+ ion and higher surface area of the Bi2MoO6 nanosheets. Therefore, this synthetic approach may exhibit a better alternative to fabricate upconversion photocatalyst for integral solar light absorption.

Upconversion emissions induced by 1550 nm in near-stoichiometric Er:LiNbO_3 crystal

To increase the photovoltaic efficiency of solar cells, green and red upconversion (UC) emissions produced at an excitation of 1550 nm were investigated. A drastically enhanced red UC emission was observed in near-stoichiometric LiNbO(3) crystal heavily doped with Er(3+) ions (Er:NSLN). Raman spectra showed that the maximum phonon energy shifted from 631 cm(-1) in Er(3+)-doped congruent LiNbO(3) (Er:CLN) to 871 cm(-1) in Er:NSLN crystal. The time decay of the (4)S(3/2)→(4)I(15/2) transition suggested that the Er(3+) cluster sites (Er(Li)(2+)-Er(Nb)(2-)) were dissociated in the Er:NSLN crystal. The visible UC luminescence converted from near infrared at the wavelength of 1550 nm was important to enlarge the solar spectrum response of solar cell.

Microwave hydrothermal synthesis and infrared to visible upconversion luminescence of Er3+/Yb3+ co-doped bismuth molybdate nanopowder

This paper reports the microwave hydrothermal synthesis and infrared to visible upconversion luminescence of Er3+/Yb3+ co-doped Bi2MoO6 nanopowder. Crystal structure, morphology and chemical composition were analyzed by means of X-ray Diffraction, Transmission Electron Microscopy and Raman Spectroscopy. Upconversion luminescence properties were studied in detail. The infrared to visible upconversion luminescence has been investigated in Er3+/Yb3+ doped Bi2MoO6 with different Yb3+ concentrations. Intense green and red upconversion emissions around 532, 545, and 655nm corresponding to the 2H11/2, 4S3/2, and 4F9/2 transitions, respectively, to the 4I15/2 ground state were observed when excited by CW laser radiation at 980nm. The effect of Yb3+ on the upconversion luminescence intensity was analyzed and the upconversion luminescence mechanism was explained in terms of the energy transfer process. From this study, it confirms that the like fluorides, and germinate glasses, metal oxide nanoparticles could also be a potential host to achieve desired upconversion luminescence.

Visible green upconversion luminescence of Li+/Er3+/Yb3+co-doped CaWO4phosphor and effects of Yb3+concentration

The upconversion (UC) luminescence of <TEX>$Li^+/Er^{3+}/Yb^{3+}$</TEX> co-doped <TEX>$CaWO_4$</TEX> phosphors and effects of <TEX>$Yb^{3+}$</TEX> concentration are investigated in detail. Single crystallized <TEX>$CaWO_4$</TEX> : <TEX>$Li^+/Er^{3+}/Yb^{3+}$</TEX> phosphor can be obtained, co-doped up to 35.0/5.0/30.0 mol% (<TEX>$Li^+/Er^{3+}/Yb^{3+}$</TEX>) by solid-state reaction. Under 980 nm excitation, <TEX>$CaWO_4$</TEX> : <TEX>$Li^+/Er^{3+}/Yb^{3+}$</TEX> phosphor exhibited strong green UC emissions visible to the naked eye at 530 and 550 nm induced by the intra 4f transitions of <TEX>$Er^{3+}$</TEX> (<TEX>$^4H_{11/2}$</TEX>, <TEX>$^4S_{3/2}{\rightarrow}^4I_{15/2}$</TEX>). The optimum doping concentrations of <TEX>$Yb^{3+}$</TEX> that would result in the highest UC luminescence were determined, and a possible UC mechanism that depends on the pumping power is discussed in detail.

Infrared to visible upconversion luminescence in Er3+/Yb3+ co-doped CeO2 inverse opal

Infrared to visible upconversion luminescence has been investigated in Er3+/Yb3+ co-doped CeO2 inverse opal. Under the excitation of 980 nm diode lasers, visible emissions centered at 525, 547, 561, 660 and 680 nm are observed, which are assigned to the Er3+ transitions of 2H11/2 → 4I15/2 (525 nm), 4S3/2 → 4I15/2 (547, 561 nm), 4F9/2 → 4I15/2 (660 and 680 nm), respectively. The effect of photonic band gap on the upconversion luminescence intensity was also obtained. Additionally, the upconversion luminescence mechanism was studied. The dependence of Er3+ upconversion emission intensity on pump power reveals that it is a two-photon excitation process.

Visible and near infrared up-conversion luminescence in Yb3+/Tm3+ co-doped yttria-alumino-silicate glass based optical fibers

We report blue light up-conversion (UC) emission in Yb–Tm co-doped nano-phase separated yttria-alumino-silicate (YAS) glass based D-shaped with low-index cladding optical fibers. Y2O3 creates an environment of nano structured YAS glass phases with Yb and Tm rich zone into the core glass which confirmed from TEM analyses. This kind of glass host assists in distributing of Yb and Tm rich zone uniformly throughout the core region. Yb and Tm doped regions exist mainly into nano YAS phases, defined as RE rich nano YAS-RE phases. All samples exhibit UC luminescence peaks at 483nm, 650nm and 817nm for Tm3+ and 1044nm for Yb3+ under excitation by 975nm laser light. In such type of nano-engineered glass–ceramic based host, almost all the Yb ions transferred its energy to the nearer Tm ions. In particular 483nm emission is attributed to 1G4→3H6 transition through a three step resonance energy transfer (ET) from excited Yb3+. The highest emission intensity is obtained with a concentration of 0.5wt% Tm3+ and 2.0wt% Yb3+. The ET between Yb3+ and Tm3+ is increased with increase of Yb3+ concentration with respect to Tm3+. The experimental fluorescence life-times of Tm3+ upconversion emission at visible wavelengths into such kind of fiber is reported under 975nm pump excitation. The present study is important for development of an efficient tunable 483nm fluorescence light source.