Efficient Upconversion Emission Research Articles

Ion-redistribution induced efficient upconversion in β-NaYF4:20%Yb3+,2%Er3+ microcrystals with well controlled morphology and size.

We develop an efficient green upconversion (UC) β-NaYF4:20%Yb3+,2%Er3+ microcrystal with well controlled morphology and size by hydrothermal method using two different chelating agents of CIT and EDTA-2Na via a simple ion-exchange reaction. Importantly, the UC emission efficiency of newly developed CIT and EDTA-2Na β-NaYF4:20%Yb3+,2%Er3+ microcrystals is almost as strong as that of commercial counterpart by solid-state method. A proof-of-concept β-NaYF4:20%Yb3+,2%Er3+ microcrystal waveguide is demonstrated to extend their applications in modern micro-optoelectronics. The local ion-redistribution process during the ion-exchange reaction, which effectively disperses the locally clustered Yb3+, accounts for the enormously enhanced UC emission in β-NaYF4:20%Yb3+,2%Er3+ microcrystals.

Lanthanide doped ultrafine hybrid nanostructures: multicolour luminescence, upconversion based energy transfer and luminescent solar collector applications.

We herein demonstrate novel inorganic-organic hybrid nanoparticles (HNPs) composed of inorganic NPs, NaY0.78Er0.02Yb0.2F4, and an organic β-diketonate complex, Eu(TTA)3Phen, for energy harvesting applications. Both the systems maintain their core integrity and remain entangled through weak interacting forces. HNPs incorporate the characteristic optical behaviour of both the systems i.e. they give an intense red emission under UV excitation, due to Eu3+ in organic complexes, and efficient green upconversion emission of Er3+ in inorganic NPs for NIR (980 nm) excitation. However, (i) an energy transfer from Er3+ (inorganic NPs) to Eu3+ (organic complex) under NIR excitation, and (ii) an increase in the decay time of 5D0 → 7F2 transition of Eu3+ for HNPs as compared to the Eu(TTA)3Phen complex, under different excitation wavelengths, are added optical characteristics which point to an important role of the interface between both the systems. Herein, the ultra-small size (6-9 nm) and spherical shape of the inorganic NPs offer a large surface area, which improves the weak interaction force between both the systems. Furthermore, the HNPs dispersed in the PMMA polymer have been successfully utilized for luminescent solar collector (LSC) applications.

Broadband NIR photoelectronic performance for sunlight‐induced photocurrent from (NaYF4:Yb‐Er)/BiOI hybrid films

AbstractThe fabrication and near‐infrared optoelectronic performance of the (NaYF4:Yb‐Er)/BiOI upconversion phosphor/semiconductor hybrid films are reported. The composite films were fabricated by a simple electro‐deposition and successive ionic layer adsorption and reaction (SILAR) method. We observed efficient upconversion emissions in the film of NaYF4:Yb‐Er upon irradiation by near‐infrared part of simulated sunlight, and the UC emission is drastically quenched in the composite film (NaYF4:Yb‐Er)/BiOI. More importantly, this composite film displays unusual negative photoresponse to near‐infrared part of simulated sunlight when used in a standard electrochemical cell where the composite film serves as the photoanode. This result may pave the way for potential application of this hybrid films for the development of novel photovoltaic and infrared optoelectronic devices.

Enormously enhanced upconversion emission in β-NaYF4:20Yb,2Er microcrystals via Na+ ion exchange

Efficient upconversion (UC) microcrystals are important for the development of novel photonic markers, solid-state lasers, displays, etc. Herein, we report on greatly enhanced UC emission in β-NaYF4:20Yb,2Er microcrystals via a simple ion-exchange reaction. The ion exchange accompanying with an ionic redistribution process is demonstrated. By simply controlling the amount of NaF (0–8.0 mmol), reaction temperature (140–220 °C), and duration (0–144 h), enormous enhancement of the UC emission up to ~4200 times is obtained compared with the pre-synthesized β-NaYF4:20Yb,2Er microcrystals. The decrease of body defects and change of local structure around lanthanide may account for the UC emission enhancement. This method may apply to other UC materials to increase the UC emission efficiency.

Tunable up-conversion luminescence from Er3+/Tm3+/Yb3+ tri-doped Sr2CeO4 phosphors

Er3+/Tm3+/Yb3+ tri-doped Sr2CeO4 phosphors have been synthesized via high-energy deformation processes. The structure of the synthesized phosphor is identified to be a pure orthorhombic structure. By varying the concentration of dopant ions (Er3+, Tm3+, Yb3+), the obtained phosphors present tunable up-conversion emissions under 975nm a laser diode excitation. The white up-conversion light emitted from a 3mol%Er3+/1mol%Tm3+/10mol%Yb3+ ions tri-doped Sr2CeO4 phosphor was observed corresponding to the transitions from 1G4→3H6 (Tm3+), 1G4→3F4 (Tm3+), 2H11/2→4I15/2 (Er3+), 4S3/2→4I15/2 (Er3+) and 4F9/2→4I15/2 (Er3+) transitions at 478, 652, 526, 552 and 664nm, respectively. The efficient up-conversion emission is attributed to energy transfer between Yb3+ and Er3+ or Tm3+ ions. Moreover, there is a chance for an energy transfer from the 4I15/2 level of the Er3+ to the 3H5 level of the Tm3+ to enhance the blue emission. The results indicate that the synthesized phosphors can be potentially applied to many devices, such as optical displays, lighting sources for light emitting diodes and lasers.

Designed Er(3+)-singly doped NaYF4 with double excitation bands for simultaneous deep macroscopic and microscopic upconverting bioimaging.

Simultaneous deep macroscopic imaging and microscopic imaging is in urgent demand, but is challenging to achieve experimentally due to the lack of proper fluorescent probes. Herein, we have designed and successfully synthesized simplex Er(3+)-doped upconversion nanoparticles (UCNPs) with double excitation bands for simultaneous deep macroscopic and microscopic imaging. The material structure and the excitation wavelength of Er(3+)-singly doped UCNPs were further optimized to enhance the upconversion emission efficiency. After optimization, we found that NaYF4:30%Er(3+)@NaYF4:2%Er(3+) could simultaneously achieve efficient two-photon excitation (2PE) macroscopic tissue imaging and three-photon excitation (3PE) deep microscopic when excited by 808 nm continuous wave (CW) and 1480 nm CW lasers, respectively. In vitro cell imaging and in vivo imaging have also been implemented to demonstrate the feasibility and potential of the proposed simplex Er(3+)-doped UCNPs as bioprobe.

A facile one-pot method to synthesize ultrasmall core-shell superparamagnetic and upconversion nanoparticles

Ultrasmall core-shell Fe3O4@NaYF4:Yb3+/Er3+ nanoparticles with bifunctional properties have been successfully synthesized via one pot thermolysis method using oleylamine as both solvent and stabilizer. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), upconversion (UC) luminescence spectra and the physical properties measurement system (PPMS) were used to characterize the resulting samples. The synthesized samples have uniform morphology with a mean size of 14.5nm and excellent dispersibility. Moreover, these nanoparticles exhibit superparamagnetic behaviour with saturation magnetization of 8.45emμ/g and efficient up-conversion emission with a two-photon induced process when excited by a 980nm laser. These results suggest that the synthesized ultrasmall bifunctional nanoparticles may find many biomedical applications, such as clinical diagnosis and treatment of cancers.

Efficient green and red up-conversion emissions in Er/Yb co-doped TiO2 nanopowders prepared by hydrothermal-assisted sol–gel process

In this work, erbium and ytterbium co-doped titanium dioxide (Er–Yb:TiO2) nanopowders have been successfully prepared by hydrothermal-assisted sol–gel method using supercritical drying of ethyl alcohol and annealing at 500°C for 1h. Nanopowders were prepared with fixed 5mol% Erbium concentration and various Ytterbium concentrations of 5 and 10mol%. The powders were characterized by studying their structural, morphology and photo-luminescent properties. The annealing treatment at 500°C was found to enhance the crystallinity of the TiO2 anatase structure and the upconversion (UC) emission of the nanopowders. UC emissions were investigated under 980nm excitation, and the Er–Yb:TiO2 nanopowders exhibited the intense green (520–570nm) and red (640–690nm) upconverted emissions of Er ions originating from an efficient Yb–Er energy transfer process. The absolute upconversion quantum yield (UC-QY) of each nanopowders was measured for the UC emissions centered at 525, 550 and 655nm at varying excitation power densities. UC-QY analysis has revealed that 5mol% Er–5mol% Yb:TiO2 nanopowders possess the highest total quantum yield of 2.8±0.1% with a power density of 16.7W/cm2. These results make these nanopowders promising materials for efficient upconversion in photonic applications.

Structure and optical properties of transparent Er3+-doped CaF2–silica glass ceramic prepared by controllable sol–gel method

Transparent Er3+-doped CaF2–silica glass ceramics were prepared by the direct physical introduction of Er3+ doped CaF2 nanocrystals into acid-catalyzed sol–gel silica glass. The physical methods of ball milling, ultrasonic baths, and stirring were investigated to disperse Er3+ doped CaF2 nanocrystals in the silica sols. The CaF2–silica sol mixture went through gelation and heat-treatment to form Er3+-doped CaF2–silica glass ceramics. The morphology of Er3+ doped CaF2 in silica glass did not change after heat-treatment at 600°C for 10h. The experimental results showed that Er3+ doped CaF2 in the glass ceramic prepared with the assistance of ball milling possesses the best dispersity and homogeneity. The highest in-line transmittance of the glass ceramic reached up to 85% in visible region. Glass ceramic exhibits efficient up-conversion emissions corresponding to the Er3+:4F9/2→4I15/2 transition and long lifetime of 4F9/2 level (1.73ms) under 980nm excitation.

Novel UV–vis-driven photocatalysts of CeF3/TiO2 nano-sheet film with upconversion properties for enhanced photocatalytic activity

Upconversion photocatalysts have the potential to extended utilization of sunlight and enhance the photocatalytic performance. A novel hybrid architecture of CeF3/TiO2 nano-sheet film (NSF) was synthesized via a facile one-step microwave-hydrothermal synthesis. The luminescence agent of CeF3 nanodisks were deposited homogeneously on the surface of the TiO2 NSF. The CeF3/TiO2 NSF composite materials show obvious photodegradation of MB under visible light as well as ultraviolet light, resulting in enhanced photocatalytic activity in the UV–vis bands solar spectrum due to the efficient upconversion emissions of CeF3. Additionally, a photocatalytic mechanism of CeF3/TiO2 NSF was proposed.

Confining energy migration in upconversion nanoparticles towards deep ultraviolet lasing.

Manipulating particle size is a powerful means of creating unprecedented optical properties in metals and semiconductors. Here we report an insulator system composed of NaYbF4:Tm in which size effect can be harnessed to enhance multiphoton upconversion. Our mechanistic investigations suggest that the phenomenon stems from spatial confinement of energy migration in nanosized structures. We show that confining energy migration constitutes a general and versatile strategy to manipulating multiphoton upconversion, demonstrating an efficient five-photon upconversion emission of Tm3+ in a stoichiometric Yb lattice without suffering from concentration quenching. The high emission intensity is unambiguously substantiated by realizing room-temperature lasing emission at around 311 nm after 980-nm pumping, recording an optical gain two orders of magnitude larger than that of a conventional Yb/Tm-based system operating at 650 nm. Our findings thus highlight the viability of realizing diode-pumped lasing in deep ultraviolet regime for various practical applications.

Effect of Defect States on the Upconversion Emission Properties in KLu2F7 Nanocrystalline

The influence of the introduction of Li+ ions on the upconversion (UC) properties of KLu2F7:Yb3+, Er3+ nanocrystalline has been investigated in detail. It is found that the UC emission intensity of 10 mol% Li+ ions doped KLu2F7:Yb3+, Er3+ nanocrystalline is enhanced about 13 times in comparison with that of Li+-free sample. Under the excitation of 980 nm laser diode (LD), a significant improvement of the green to red emission ratio (GRR) in the 10 mol% Li+-doped sample is observed by increasing pump power density. Li+ ions could occupy the cationic sites or the interstitial sites in the KLu2F7 host matrix, which probably eliminate the defect states via the charge compensation and tailor of the crystal field, leading to the promotion of the UC emission efficiency. Thus, the introduction of Li+ ions provides new opportunities for enhancing the scope of applications of Yb3+, Er3+ doped KLu2F7 nanocrystalline ranging from infrared solar cells to volumetric multiplexed bio-probe.

Tumor Imaging Based on Photon Upconversion of Pt(II) Porphyrin Rhodamine Co-modified NIR Excitable Cellulose Enhanced by Aggregation.

We report a bioinspired upconversion (UC) system using a cellulose template, in which an aggregated platinum(II)-tetraphenylporphyrin (PtTPP) sensitizer is able to excite Rhodamine B as an emitter, enabling near-infrared (NIR)-to-orange wavelength conversions. The comodified cellulose was observed to undergo J aggregation of PtTPP in DMSO solution, as indicated by broad, weak absorption bands in the NIR region of the absorption spectrum. Excitation of these NIR J aggregation peaks of PtTPP led to efficient UC emission in the orange wavelength region. These materials were shown to exhibit UC properties in biological settings both in vitro and in vivo, demonstrating utility of UC for tumor imaging.

Mechanochemical preparation of nanocrystalline NaYF4:Gd3+/Yb3+/Tm3+: An efficient upconversion phosphor

We report on a mechanochemical preparation route for NaYF4:Gd3+/Yb3+/Tm3+ nanoparticles by ball-milling NaF, YF3, GdF3, YbF3 and TmF3 at room temperature. An analysis by XRD and TEM demonstrates that the resulting materials are mainly (∼88% after 4h ball-milling) in the hexagonal phase and are on the nanoscale with an average crystallite size of ∼20nm. The prepared nanoparticles display efficient upconversion emission; upon excitation by a 980nm laser diode, bright visible blue light emission can be observed. However, in accord with previous results, the strongest emission is observed in the NIR at 800nm.

Up-conversion luminescent properties and optical thermometry of LaMgAl11O19: Yb3+/Er3+ phosphors

LaMgAl11O19: Yb3+/Er3+ phosphors were successfully synthesized by a conventional sol–gel method with a lower temperature. The composition and phase purity of the samples were examined by X-ray diffraction (XRD). Under 980nm excitation, the phosphors exhibited efficient visible up-conversion (UC) emissions including strong green emission centered at 525, 545nm, and weak red emission centered at around 657nm, which were assigned to the 2H11/2→ 4I15/2, 4S3/2→ 4I15/2 and 4F9/2→ 4I15/2 transitions of Er3+ ions, respectively. The process involved in the UC emission was evaluated in detail by energy level diagram and the pump power dependence. To investigate the sensing application of the synthesized phosphor materials, temperature-sensing performance was studied in the temperature range of 298–573K using the fluorescence intensity ratio technique. The maximum sensitivity was found to be approximately 0.00267K−1, indicating its applicability as an optical temperature sensor.

ChemInform Abstract: Lab on Upconversion Nanoparticles: Optical Properties and Applications Engineering via Designed Nanostructure

AbstractReview: 268 refs.

Preparation and Upconversion Luminescence Characterization of Eu3+/Yb3+ Codoped 12CaO · 7Al2O3 Ceramics

Eu3+/Yb3+ codoped 12CaO · 7Al2O3 (C12A7) ceramics were prepared via high temperature solid-state reaction method, and characterized by X-Ray powder diffraction. Under the excitation of 980 nm laser radiation, efficient upconversion emissions were observed in 450–900 nm region and attributed to the 5DJ→7FJ transitions of Eu3+ ions. The proposed upconversion emission mechanism involves the two-photon cooperative upconversion process. The effects of Yb3+ ions on the upconversion emission follow a concentration-dependent manner. The Commission Internationale de I'eclairage (CIE) chromaticity coordinates (x, y) illustrate the color of emissions can be tunable to purer green by increasing the Yb3+ concentration.

TPGS-stabilized NaYbF4:Er upconversion nanoparticles for dual-modal fluorescent/CT imaging and anticancer drug delivery to overcome multi-drug resistance

Multi-drug resistance (MDR) is a major cause of failure in cancer chemotherapy. Tocopheryl polyethylene glycol 1000 succinate (TPGS) has been extensively investigated for overcoming MDR in cancer therapy because of its ability to inhibit P-glycoprotein (P-gp). In this work, TPGS was for the first time used as a new surface modifier to functionalize NaYbF4:Er upconversion nanoparticles (UNCPs) and endowed the as-prepared products (TPGS-UCNPs) with excellent water-solubility, P-gp inhibition capability and imaging-guided drug delivery property. After the chemotherapeutic drug (doxorubicin, DOX) loading, the as-formed composites (TPGS-UCNPs-DOX) exhibited potent killing ability for DOX-resistant MCF-7 cells. Flow-cytometric assessment and Western blot assay showed that the TPGS-UCNPs could potently decrease the P-gp expression and facilitate the intracellular drug accumulation, thus achieving MDR reversal. Moreover, considering that UCNPs process efficient upconversion emission and Yb element contained in UCNPs has strong X-ray attenuation ability, the as-obtained composite could also serve as a dual-modal probe for upconversion luminescence (UCL) imaging and X-ray computed tomography (CT) imaging, making them promising for imaging-guided cancer therapy.

Three- and two-photon upconversion luminescence switching in Tm3+/Yb3+-codoped sodium niobate nanophosphor

Intense infrared-to-visible upconversion (UC) emission in Tm 3+ /Yb 3+ -codoped sodium niobate (NaNbO 3 ) nanocrystals under resonant excitation at 976 nm is presented. The results showed that by increasing the pump power/intensity, a strong reduction is observed at the 800/480 nm emitted intensity ratio, characterizing what can be denominated as laser pump power-induced color tunability or luminescent switching. The physical origin is discussed with a focus on tailoring of luminescent switchers to operate at a large pump power range and, indeed, it is intrinsically associated with the competition of the two- and three-photon UC processes and with highly efficient UC emissions in the investigated material. The effect of Yb 3+ -ion concentration along with the theoretical aspects on luminescence switching has been investigated. The results obtained here could be useful in the field of sensors and networks for optical processing and optical communications.

Near-infrared photocatalysts of BiVO4/CaF2:Er3+, Tm3+, Yb3+with enhanced upconversion properties

Upconversion photocatalysts have the potential to absorb the near-infrared (NIR) light in solar energy and improve the photocatalytic performance. A hierarchical upconversion photocatalyst of BiVO₄ (BVO)/CaF₂:Er(3+), Tm(3+), Yb(3+) (CF) combined with the narrow-band semiconductor of BVO and the luminescence agent of CF to enhance upconversion properties was synthesized via the hydrothermal method. The CF particles were deposited homogeneously on the surface of the BVO/CF composite with regular dendritic structure, which led to efficient upconversion emissions. The upconversion emission intensity of the BVO/CF composite was 8 times higher than that of pure CF, through tailoring the crystal symmetry of lanthanide ions by Bi(3+) ions. The upconverted ultraviolet (361 and 379 nm), violet (408 nm), and blue (485 nm) light was able to excite BVO for photocatalysis in BVO/CF under NIR irradiation, which improved the degradation rate of methyl orange (MO).