Energy Transfer Upconversion Research Articles

Upconversion Luminescence Properties of Y2O3:Yb, Er and Y2O2S:Yb, Er Nanoparticles Prepared by Complex Precipitation

The Yb3+, Er3+ doped Y2O3 and Y2O2S upconversion nanophosphors were prepared by the direct complex precipitation method with the mixed solution of NH4HCO3 and NH3·H2O as the complex precipitant. The precipitate of calcined at 900°C in air presents the pure Y2O3 with cubic structure, and the calculated crystalline size is about 26 nm, while the Y2O2S:Yb, Er nanocrystals were obtained by annealing the same precipitate at 900°C but in the atmosphere of N2 gas containing sulfur vapor. The obtained sample presents the pure hexagonal structure of Y2O2S with calculated crystalline size of 29 nm. According to the transmission electronic microscopy (TEM), the nanophosphors exhibit uniform quasispherical shape and size about 30 nm. By using the 980 nm excitation laser, the properties of upconversion luminescence and energy transfer processes were studied in detail for the different concentration of Yb3+ in Er3+ doped Y2O3 as well as the Yb3+, Er3+ codoped Y2O2S nanocrystals. The high‐efficient red and yellow upconversion emissions were both observed by naked eyes in day time corresponding to the Y2O3:Yb, Er and Y2O2S:Yb, Er phosphors, respectively. Thus the upconversion nanoparticles combining its high efficient emission would pave the way for ideal fluorescence probes in biological applications.

Measuring the Elevated Temperature Dependence of Up-Conversion in Nd:YAG

We present the measurement of the energy transfer upconversion coefficient temperature-dependence from the main upper laser level (4F3/2) of 1at.% doped Nd:YAG. This is achieved by a very simple method employing the z-scan technique, through monitoring the transmitted power of a probe laser tuned to the main absorption peak at 808 nm. In addition, to fully develop a simple model to support the measurements, we have accurately measured the temperature dependent absorption coefficient for this absorption band, covering the range from 300-450K. The spatially dependent two-level rate equation model is described, which simulates the relationship between the incident pump irradiance and power transmitted by the crystal, in function of its temperature. By comparing the experimental results with the model, we obtain a value for the energy transfer upconversion coefficient of 5.1±0.4 ×10-17 cm3/s, at room temperature, decreasing to 2.0 ×10-17 cm3/s at 450 K.

Observation of efficient population of the red-emitting state from the green state by non-multiphonon relaxation in the Er3+–Yb3+ system

AbstractThe rare earth Er3+ and Yb3+ codoped system is the most attractive for showcasing energy transfer upconversion. This system can generate green and red emissions from Er3+ under infrared excitation of the sensitizer Yb3+. It is well known that the red-emitting state can be populated from the upper green-emitting state. The contribution of multiphonon relaxation to this population is generally considered important at low excitation densities. Here, we demonstrate for the first time the importance of a previously proposed but neglected mechanism described as a cross relaxation energy transfer from Er3+ to Yb3+, followed by an energy back transfer within the same Er3+–Yb3+ pair. A luminescence spectroscopy study of cubic Y2O3:Er3+, Yb3+ indicates that this mechanism can be more efficient than multiphonon relaxation, and it can even make a major contribution to the red upconversion. The study also revealed that the energy transfers involved in this mechanism take place only in the nearest Er3+–Yb3+ pairs, and thus, it is fast and efficient at low excitation densities. Our results enable a better understanding of upconversion processes and properties in the Er3+–Yb3+ system.

Photon energy upconversion through thermal radiation with the power efficiency reaching 16%.

The efficiency of many solar energy conversion technologies is limited by their poor response to low-energy solar photons. One way for overcoming this limitation is to develop materials and methods that can efficiently convert low-energy photons into high-energy ones. Here we show that thermal radiation is an attractive route for photon energy upconversion, with efficiencies higher than those of state-of-the-art energy transfer upconversion under continuous wave laser excitation. A maximal power upconversion efficiency of 16% is achieved on Yb(3+)-doped ZrO2. By examining various oxide samples doped with lanthanide or transition metal ions, we draw guidelines that materials with high melting points, low thermal conductivities and strong absorption to infrared light deliver high upconversion efficiencies. The feasibility of our upconversion approach is further demonstrated under concentrated sunlight excitation and continuous wave 976-nm laser excitation, where the upconverted white light is absorbed by Si solar cells to generate electricity and drive optical and electrical devices.

Er<sup>3+</sup> Upconversion Fluorescence of ErNbO<sub>4</sub> Phosphor for Optical Temperature Sensing

Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> upconversion (UC) fluorescent characteristics of ErNbO4 phosphor were studied for temperature sensing purposes. This letter shows that the ErNbO4 phosphor emits more UC fluorescence than the Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped LiNbO3 single-crystal and Er3NbO7 phosphor. Both energy-transfer UC and excited state absorption play a role in the UC emission. Both the peak and integrated UC intensities decrease with the raised temperature, and the 530, 560, and 670 nm UC intensities reduce by \(\sim 26\) %, 42%, and 34%, respectively, with the temperature rise of only 57 °C from 21 °C, implying that the phosphor is applicable to temperature sensing based upon either the 560- or 670-nm emission. The feasibility to realize the temperature sensing is discussed from the application requirements of smartness and low-cost, suggesting that not only the single 560- or 670-nm band, but the combined 530- and 560-nm bands can be also utilized.

Mid-infrared fluorescence, energy transfer process and rate equation analysis in Er3+ doped germanate glass.

Er3+ doped Y2O3 and Nb2O5 modified germanate glasses with different Er3+ concentrations were prepared. J-O intensity parameters were computed to estimate the structural changes due to the additions of Y2O3 and Nb2O5. The main mid-infrared spectroscopic features were investigated. To shed light on the observed mid-infrared radiative behavior, 975 nm and 1.53 μm emission spectra along with their decay lifetimes were also discussed. Moreover, the energy transfer processes of 4I11/2 and 4I13/2 level were quantitatively analyzed. In view of the experimental lifetimes, the simplified rate equation was utilized to calculate the energy transfer upconversion processes of upper and lower laser level of 2.7 μm emission. The theoretical calculations are in good agreement with the observed 2.7 μm fluorescence phenomena. Finally, the stimulated emission and gain cross sections were calculated and the results indicate that Er3+ doped germanate glasses have great potential for mid-infrared application.

Abnormal Visible Luminescence Mechanism of Tb3+-Yb3+ Codoped SiO2-Al2O3-CaF2 Glass Studied by Time-Resolved Spectra

The upconversion energy transfer mechanism in Tb3+-Yb3+ co-doped SiO2-Al2O3-CaF2 glass is investigated by time-resolved spectra. The effect of donor ion Yb3+ is involved in the dynamic decay behavior of acceptor ion Tb3+, which provides direct proof for the energy transfer from Yb3+ to Tb3+. The pump power dependence curves show that the upconversion luminescence is a two-photon process. The measured decay curves of the 5D4 state (Tb3+) contain two parts: a slow decay process corresponding to its radiation, and a fast one with a decay parameter approximately twice the lifetime of the 2F5/2 state (Yb3+). The fast decay process is contradictory to the generally accepted cooperative sensitization upconversion rate equation model. Since the effect of the host environmental is excluded by comparative experiments, we believe that there should be another energy transfer mechanism in Tb3+-Yb3+ co-doped SiO2-Al2O3-CaF2 glass in addition to the cooperative sensitization process.

Infrared-to-visible up-conversion luminescence and energy transfer of RE3+/Yb3+(RE = Ho, Tm) co-doped SrIn2O4

Near-infrared excited up-conversion phosphors of RE3+/Yb3+(RE=Ho, Tm) co-doped SrIn2O4 were synthesized by a solid-state reaction method. X-ray diffraction analysis revealed the phase composition of those samples, and the up-conversion spectroscopic properties were studied in terms of up-conversion emission spectra. Under 980nm near-infrared laser excitation, strong green emission with the peak at 546nm was observed in SrIn2O4: Ho3+/Yb3+, which can be assigned to the characteristic 5S2(5F4)→5I8 transition of Ho3+. Furthermore, SrIn2O4: Tm3+/Yb3+ showed bright blue emission with the peak at 486nm, which is associated with the 1G4→3H6 transition of Tm3+. The UC power studies indicated that the luminescence of SrIn2O4: Ho3+/Yb3+ and SrIn2O4: Tm3+/Yb3+ are attributed to two-photon and three-photon process, respectively. The possible UC luminescence mechanism and energy transfer in SrIn2O4: RE3+/Yb3+ were discussed.

Effect of Mn2+ ions on the enhancement red upconversion emission of Mn2+/Er3+/Yb3+ tri-doped in transparent glass-ceramics

Abstract The glass and glass-ceramics samples with composition of 50SiO2–10AlF3–(30−x)BaF2–5TiO2–3.95LaF3– xMnCO3–0.05ErF3–1YbF3 (in mol%, x=0, 0.5, 0.8, 1.0, and 1.2) were prepared using the conventional quenching techniques. The effects of Mn2+ ions on the enhancement red upconversion emission of Mn2+/Er3+/Yb3+ tri-doped transparent glass-ceramics under the changing of heat treatment temperatures and concentrations of Mn2+ ions were investigated. The structural investigation carried out by X-ray diffraction (XRD), and transmission electron microscopy evidenced the formation of cubic Ba2LaF7 nanocrystals. The efficiency upconversion emission of Mn2+/Er3+/Yb3+ tri-doped was observed in the glass-ceramics. The upconversion mechanism and energy transfer between Mn2+–Yb3+ dimer and Er3+ ions were investigated.

Electrochemical and structural analysis of the RE3+:CeO2 nanopowders from combustion synthesis

The reported article deals with the synthesis and characterization of rare earth ions doped ceria (RE3+:CeO2) nanopowders from citrate nitrate auto-combustion route. The crystalline nature and lattice planes of the nanocrystalline RE3+:CeO2 powders were analyzed by X-ray diffraction (XRD) and Selected Area Electron Diffraction (SAED) profile fit. The excited state absorption (ESA) and energy transfer up-conversion (ETU) were studied by photoluminescence (PL) measurement. The spectroscopic properties of the powders were studied using Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The surface morphology, average size, distribution and orientation of the lattice planes of the nanoparticles were studied by using scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The size of RE3+:CeO2 nanoparticles were found to be in the range from 15 to 30nm which has good agreement with the HRTEM results. The changes in current density with increasing sweep scan potential of the doped ceria powders were studied by cyclic voltammetry (CV) analysis. The specific capacitance range of the rare earths doped ceria of Er:CeO2, Pr:CeO2, Yr:CeO2 and Nd:CeO2 were calculated as (12.9–86.5), (20–72.4), (80–375) and (0.92–4.22) respectively.

Multicolor upconversion emission and energy transfer mechanism in Er3+/Tm3+/Yb3+ codoped tellurite glasses

A novel Er3+, Tm3+ and Yb3+ codoped tellurite glasses with composition of TeO2–Bi2O3–ZnO–Na2O was prepared by conventional melt-quenching technique to realize the multicolor upconversion (UC) emissions. The absorption spectrum, UC emission spectrum, Raman spectrum, X-ray diffraction (XRD) and differential scanning calorimeter (DSC) curves were measured to characterize the prepared glass samples. Under the excitation of 980nm laser diode (LD), bright multicolor luminescence composed of red, green and/or blue UC emissions corresponding to the transitions 4F9/2→4I15/2, 2H11/2(4S3/2)→4I15/2 of Er3+ and 1G4→3H6 of Tm3+ were observed in the Er3+/Yb3+, Tm3+/Yb3+ and Er3+/Tm3+/Yb3+ codoped glass samples, which were mainly attributed to the successive energy transfers from Yb3+ to Er3+ and Tm3+, respectively. The energy transfer mechanisms from the Yb3+:2F5/2 level to Er3+:4I11/2 and Tm3+:3H5 levels were further investigated by quantitatively calculating the energy transfer micro-parameters and phonon contribution ratios. Meanwhile, the difference (ΔT=Tx−Tg) between the glass crystallization onset temperature (Tx) and the transition temperature (Tg) which increase slightly with rare-earth (RE) doped concentration, was larger than 140°C for all glass samples. Furthermore, the amorphous nature of glass structure was demonstrated by the measured XRD curves. The excellent thermal stability and multicolor luminescent characteristic indicate that the present investigated Er3+/Tm3+/Yb3+ codoped tellurite glasses could be used in the fields of solid state multicolor displays and other luminescent devices.

Rare earth silicates as gain media for silicon photonics [Invited

ErxY2−xSiO5 and ErxYbyY2−x−ySiO5 crystalline thin films were investigated to apply to the high-gain media for silicon photonics. In addition to the sol–gel method, the directed self-assembly approach, using layer-by-layer deposition techniques, was also introduced to improve the crystallinity. The relaxation processes in Er ions were discussed to clarify the contribution of the energy transfer and cooperative upconversion. After optimization of the Er content, a Si photonic crystal slot ErxY2−xSiO5 waveguide amplifier was fabricated, and a 30 dB/cm modal gain was demonstrated. This achievement demonstrates the potential for compact and high optical gain devices on Si chips.

Yellow to violet upconversion processes of Nd3+ in neat Cs2NaNdCl6 elpasolite

Yellow to violet upconversion of Nd3+ in neat Cs2NaNdCl6 elpasolite is demonstrated in this paper. Three intense bands have been observed at 367, 390 and 422nm originating from 4D3/2 multiplet upon the excitation of 595.5nm, which is in resonance with the energy of 4G5/2 level of Nd3+. The mechanism of the upconversion has been investigated through upconversion emission intensity dependence on the power of the pumping light and luminescence decay. It is found out that the upconversion is a two-photon process. The ground state absorption (GSA)/energy transfer upconversion (ETU) is responsible for the upconversion with comparison of the excitation spectrum and the one-photon absorption spectrum.

Photon Upconversion in a Molecular Lanthanide Complex in Anhydrous Solution at Room Temperature

Molecular photon upconversion luminescence was observed from an ion-associated complex of an erbium chelate of 2-thenoyltrifluoroacetone and a near-infrared-emitting cyanine dye in anhydrous solution at room temperature. In the complex erbium was sensitized by the organic antenna dye excited at 808 nm. The result was characteristic erbium emission at 510–565 nm with second-order dependence on the excitation power, suggesting a dye-sensitized energy transfer upconversion mechanism. Compared to inorganic upconverting nanoparticles, the organic molecular dye-sensitized complexes are expected to offer higher molar absorptivity, smaller well-defined size, and simpler addition of functional groups.

Cosolvent-Free Sol–Gel Synthesis and Optical Characterization of Silica Glasses Containing LaF3 and (La,Er)F3 Nanocrystals

Abstract Monolithic transparent silica glasses containing LaF3 nanocrystals were prepared by a cosolvent-free sol–gel method based on the pyrolysis of lanthanum trifluoroacetate. The two-step mixing of alkoxide and water, consisting of partial hydrolysis under acidic conditions and subsequent neutralization to catalyze the polycondensation of hydrophobic silica oligomers, makes it possible to shorten the processing time while eliminating the need for cosolvents. The size of the LaF3 nanocrystals decreases with an increase in the volume fraction of LaF3. This suppresses Rayleigh scattering and improves transparency at LaF3-rich compositions. Green and red upconversion photoluminescence (PL) bands, mainly caused by energy-transfer upconversion (ETU), are observed in Er-doped samples under excitation at 980 nm. The PL intensity drastically increases with an increase in the volume fraction of the LaF3 phase as a result of improved crystallinity of LaF3. The quantum yields recorded for the green and red upconversion PL bands were ca. 0.08% and ca. 0.04%, respectively.

Controllable synthesis and upconversion emission of ultrasmall near-monodisperse lanthanide-doped Sr2LaF7 nanocrystals

Fluorite phase Sr2LaF7 nanocrystals (NCs) were synthesized via solvothermal method using oleic acid as capping ligands. The effects of preparing conditions on the phase structure, crystal size, morphology, and upconversion (UC) emission properties of the products were studied. The results reveal that just apropos NaOH content facilitates the growth of near-monodispersed pure phase Sr2LaF7 NCs, and Yb3+ doping is favorable to the formation of pure Sr2LaF7 phase with more uniform size distribution. The average crystalline size of the products can be controlled less than 10nm. Following appropriate lanthanide ions doping, the NCs show intense blue, yellow, and white-color UC emission under the excitation of a 980nm laser. The energy transfer UC mechanisms for the fluorescent intensity were also investigated.

Hydrothermal synthesis and photoluminescence properties of cerium-doped cadmium tungstate nanophosphor

The present paper reports synthesis and photoluminescence studies of cadmium tungstate (CdWO4) and cerium-doped cadmium tungstate. The samples were synthesised by low cost and low temperature hydrothermal method and characterised by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and photoluminescence analysis. XRD pattern reveals that the CdWO4 has monoclinic wolframite structure. The FTIR spectrum of cerium-doped CdWO4 exhibits broadband below 700 cm−1 which is due to the δ (Ce–O–C) mode. The TEM images show that size of particle is approximately 60–120 nm in both samples. A broad intense peak was observed at 474 nm when the samples were excited with 263 nm. A broad intense peak was observed at 475 nm when the samples were excited with 600 nm. The intensity of the 474 nm peak decreases with increase in cerium doping concentration. The observation of 475 nm peak when excited with 600 nm is upconversion luminescence. This upconversion emission is due to energy transfer upconversion process involving Cd2+ ions and [WO6]6− ions. Ce3+ ion is responsible for the peak shift of 6 nm.

Up-conversion luminescence properties and energy transfer of Er3+/Yb3+ co-doped oxyfluoride glass ceramic containing CaF2 nano-crystals

The Er3+/Yb3+ co-doped transparent oxyfluoride glass-ceramics containing CaF2 nano-crystals were successfully prepared. After heat treatments, transmission electron microscopy (TEM) images showed that CaF2 nano-crystals of 20–30 nm in diameter precipitated uniformly in the glass matrix. Comparing with the host glass, high efficiency upconversion luminescence of Er3+ at 540 nm and 658 nm was observed in the glass ceramics under the excitation of 980 nm. Moreover, the size of the precipitated nano-crystals can be controlled by heat-treatment temperature and time. With the increase of the nano-crystal size, the intensity of the red emission increased more rapidly than that of the green emission. The energy transfer process of Er3+ and Yb3+ was convinced and the possible mechanism of Er3+ up-conversion was discussed.

Broadband Cr^3+-sensitized upconversion luminescence in La_3Ga_5GeO_14: Cr^3+,Yb^3+,Er^3+

Broadband-light-sensitized upconversion (UC) photon management phenomenon in La3Ga5GeO14:Cr3+,Yb3+,Er3+ is reported, featuring the concentrated broadband noncoherent light excitable at room temperature. Energy transfer among Cr3+/Yb3+/Er3+ in the Stokes and UC luminescence processes reveals that Yb3+ as a “bridge” is requisite for Cr3+-sensitized UC luminescence of Er3+. Low Cr3+ contents are preferred for UC luminescence of Yb3+-Er3+, since it would be quenched by high Cr3+ contents. The designed UC emissions 2H11/2→4I15/2 and 4S3/2→4I15/2 of Er3+ at around 510 ~560 nm are proposed to through Energy transfer upconversion (ETU) mechanism based on the Cr3+-Yb3+ dimer model with superexchange interaction according to crystallographic data and the decay curves of Er3+ UC emission. This research may open up a new perspective to design novel photonic materials excitable by broadband noncoherent light for improving the photoresponse of solar cells.

Solvothermal synthesis of CeO2:Er/Yb nanorods and upconversion luminescence characterization

CeO2:Er/Yb nanorods as upconversion materials were successfully synthesized by solvothermal method. The structures and morphologies of the CeO2:Er/Yb nanorods were characterized by XRD, SEM, HRTEM. The nanorods emitted two kinds of visible lights: the green (2H11/2, 4S3/2⟶4I15/2) and the red (4F9/2⟶4I15/2), under excitation with a continuous wave laser in the near-infrared at 980nm at room temperature. The mechanism of different emissions was explored involving excited-state absorption (ESA) and energy transfer (ET) upconversion.