Upconversion Properties Research Articles

Growth, structure and upconversion properties of Yb3+ and Er3+ co-doped Gd3Sc2Al3O12 crystal

Upconversion luminescent materials exhibit excellent near-infrared to visible conversion properties that make them crucial for optoelectronics, visible display devices, and biological labels. Herein, we report a high-quality Yb3+ and Er3+ co-doped Gd3Sc2Al3O12(GSAG) single crystal which was grown successfully by the traditional Czochralski method with Er3+ and Yb3+ doping concentration of 1 at.% and 10 at.%, respectively. The structure parameters of the crystal were observed by the X-ray Rietveld refinement method. In addition, the transmission and upconversion emission properties of the crystal were analyzed at room temperature. The 940 nm excited upconversion energy transfer mechanism and dependence of the green-to-red upconversion intensity ratio (Ig/r) on pump power were investigated. A dominant two-photon absorption process of the green and red upconversion emission bands were revealed in Yb,Er:GSAG crystal. The results indicate the crystal is a promising upconversion single crystalline material.

Three-dimensional NaYF4:Yb3+/Tm3+ hexagonal prisms coupled with ZnIn2S4 nanosheets for boosting near-infrared photocatalytic H2 evolution

Most of the solar spectrum is the near-infrared (NIR) light region, which is rarely studied in the field of photocatalysis. Herein, ZnIn2S4 nanosheets were coated on the surface of NaYF:Yb3+/Tm3+ hexagonal prisms to prepared NaYF:Yb3+/Tm3+@ZnIn2S4 (NYF@ZIS) composite for photocatalytic H2 evolution under NIR irradiation. Performance test exhibits the hydrogen production rate of NYF@ZIS is 17.81 μmol/g/h, which is better than the previously reported NIR-driven photocatalysts. The excellent NIR photocatalytic H2 evolution performance is mainly due to the combination the NYF hexagonal prisms with up-conversion property and ZIS nanosheets, which not only relieves the agglomeration of ZIS nanosheets, but also transforms the NIR into UV–vis light through the energy resonance transfer process, thus achieving NIR-driven photocatalytic H2 evolution in the NYF@ZIS system. This work not only broadens the light absorption range of ZIS photocatalyst to NIR light region for water splitting, but also provides more possibilities to utilize and convert solar energy.

Achieving efficient photocatalytic uranium extraction within a record short period of 3 min by Up-conversion erbium doped ZnO nanosheets

As an important strategic resource and environmental pollutant, uranium has high toxicity and economic value. Photocatalytic reduction of soluble hexavalent uranium (U(VI)) is a green and economic method to achieve uranium extraction, whereas the reported photocatalyst commonly requires a long period of > 1 h to reach a high extraction efficiency (>90%). Herein, we reported the ultrafast photocatalytic uranium extraction by up-conversion Er doped ZnO nanosheets. In the initial U(VI) concentration of 200 mg/L, the Er doped ZnO with 4% doping level (Er0.04-ZnO) nanosheets achieved 91.8% within 3 min, which was at least a magnitude shorter relative to ever-reported materials. The Er0.04-ZnO nanosheets reached a high removal efficiency of 96.1% in 10 min, with a considerable U(VI) extraction capacity of 3036 mg/g. The mechanistic study showed that the Er doping induced the up-conversion properties and increases the carrier density, thus enhancing the light adsorption and accelerating the U(VI) extraction.

Synthesis of upconverting nanosheets derived from Er-Yb and Tm-Yb Co-doped layered perovskites and their layer-by-layer assembled films

Here, we investigated the structure and upconversion (UC) properties of new-type of single oxide nanosheets, derived from the Er3+/Yb3+ and Tm3+/Yb3+ co-doped Ruddlesden-Popper type layered perovskites, and their layer-by-layer (LBL) self-assembled nanofilms. The single oxide nanosheets, obtained by exfoliation of the proton-exchanged K2La2Ti3O10, had the thickness in the range of 2–3 nm indicating good consistency with the theoretical thickness and lateral size from 500 nm up to 2 µm. Er3+/Yb3+, Tm3+/Yb3+ and Tm3+/Er3+co-doped nanosheets were used as building blocks of the multilayer films deposited by layer-by-layer procedure. The LBL films composed of 2.5 % Er3+ + 5 % Yb3+, 2.5 % Tm3+ + 20 % Yb3+, 2.5 % Tm3+ + 20 % Er3+ after 60 sequences have shown a white emission confirmed by the CIE chromaticity diagram. The possible UC energy transfer of LBL films fabricated after 30 sequences using the nanosheets derived from the 2.5 % Er3+ + 5 % Yb3+ co-doped layered perovskites was also suggested. The number of photons participating in the UC process was confirmed as two-photon for both green and red UC emissions due to the 4F9/2 →4I15/2 and 2H11/2, 4S3/2→ 4I15/2 transitions, respectively.

Controlling the Energy‐Transfer Processes in a Nanosized Molecular Upconverter to Tap into Luminescence Thermometry Application

AbstractPhoton upconversion (UC) in molecular species remains a highly sought‐after property with vast potential applications in many fields. Until now, a few reports on molecular upconverters are limited to demonstrating upconversion. The low UC quantum yields (QY) and nuclearities hindered the application capabilities for molecular upconverters. To overcome these limitations, we report the use of a molecular cluster‐aggregate (MCA) containing 20 lanthanide ions to target YbIII‐TbIII‐based cooperative UC. Upconversion quantum yield value of 1.04×10−4 %, among the highest value observed for a molecular cooperative UC, was attained for the{Gd11Tb2Yb7}composition. Substitution of GdIIIions for EuIIIcenters opens a YbIII→TbIII→EuIIIenergy‐transfer pathway, allowing the first proof‐of‐concept of potential application for molecular UC. This report on upconversion‐based luminescence thermometry in a molecular species endorses further development of upconversion properties of nanoscale MCAs.

Controlling the Energy-Transfer Processes in a Nanosized Molecular Upconverter to Tap into Luminescence Thermometry Application.

Photon upconversion (UC) in molecular species remains a highly sought-after property with vast potential applications in many fields. Until now, a few reports on molecular upconverters are limited to demonstrating upconversion. The low UC quantum yields (QY) and nuclearities hindered the application capabilities for molecular upconverters. To overcome these limitations, we report the use of a molecular cluster-aggregate (MCA) containing 20 lanthanide ions to target YbIII -TbIII -based cooperative UC. Upconversion quantum yield value of 1.04×10-4 %, among the highest value observed for a molecular cooperative UC, was attained for the {Gd11 Tb2 Yb7 } composition. Substitution of GdIII ions for EuIII centers opens a YbIII →TbIII →EuIII energy-transfer pathway, allowing the first proof-of-concept of potential application for molecular UC. This report on upconversion-based luminescence thermometry in a molecular species endorses further development of upconversion properties of nanoscale MCAs.

Achieving Up-Conversion Amplified Spontaneous Emission through Spin Alignment between Coherent Light-Emitting Excitons in Perovskite Microstructures

Metal hybrid perovskites have presented interesting infrared-to-visible up-conversion light-emitting lasing properties through multi-photon absorption. Here, when the optical pumping switches between circular and linear polarization, up-conversion amplified spontaneous emission (ASE) intensity exhibits large and small amplitudes, respectively, leading to a positive up-conversion ΔASE in the CsPbBr3 perovskite microrods. This observed phenomenon demonstrates that the coherent interaction between coherent light-emitting excitons is indeed established at the up-conversion ASE regime in the CsPbBr3 perovskite microrods. In addition, the positive up-conversion ΔASE indicates the orbital magnetic dipoles between coherent light-emitting excitons are conserved during up-conversion ASE action. Essentially, the up-conversion ΔASE results provide evidence that shows up-conversion ASE can be realized by the orbit−orbit polarization interaction between light-emitting excitons. Moreover, up-conversion ASE proportionally increased as the pumping fluence increased, which shows that orbit–orbit polarization interaction can be gradually enhanced between coherent light-emitting excitons by increasing pumping density in the CsPbBr3 perovskite microrods. Substantially, our studies provide a fundamental understanding of the spin alignment between coherent light-emitting excitons towards developing spin-dependent nonlinear lasing actions in metal halide perovskites.

Temperature sensing properties of NaYTiO4: Yb/Tm phosphors based on near-infrared up-conversion luminescence

In this study, NaYTiO4: Yb/Tm phosphors with different concentrations of Yb3+ and Tm3+ ions were synthesized by conventional solid-state reaction. Upon a 980 nm laser excitation, the up-conversion luminescence properties in a wide temperature range (303–823 K) were investigated. By employing the fluorescence intensity ratio (FIR) techniques based on the robust near-infrared emissions of thermally coupled 3F2,3/3H4 energy levels and 3H4(1)/3H4(2) Stark energy levels, the calculated absolute sensitivity (Sa), relative sensitivity (Sr), and temperature uncertainty (δT) values demonstrated good temperature sensing properties. For the 3F2,3/3H4 energy levels, the maximum Sr and minimum δT values are 1.04% K−1 and 0.010 K at 463 K, respectively. Moreover, the maximum Sa is 0.32 × 10−3 K−1 at 823 K. In addition, the thermally coupled 3H4 Stark energy levels present the maximum Sa, Sr and the minimum δT are 0.88 × 10−3 K−1, 0.60% K−1 and 3.17 K at 303 K, respectively. Besides, due to the ratio of blue to red emission varying with elevated temperature, the NaYTiO4: Yb/Tm phosphors are expected to be applied as an intuitive high-temperature indicator.

In situ-generated H2O2 with NCQDs/MIL-101(Fe) by activating O2: A dual effect of photocatalysis and photo-Fenton for efficient removal of tetracyline at natural pH

Herein, a novel composite of MIL-101(Fe) loaded with nitrogen doped carbon quantum dots (NCQDs/MIL-101(Fe), denoted as NQML), which can construct dual effect of photocatalysis and photo-Fenton for organic pollutants removal, was prepared by solvent impregnation method. Characterization methods proved that NQML had been synthesized successfully. Additionally, the adding volume of NCQDs could effectively influence the photocatalytic activities of NQML-x composites (x represents the adding volume of NCQDs) for tetracycline (TC) degradation, and NQML-8 exhibited the optimum photocatalytic performance among the studied catalysts upon visible light illumination under natural pH, which can completely degrade TC within 180 min. By comparison, the TC degradation kinetic constant in the system with NQML-8 was as 15.85 and 8.24 folds of that in the NCQDs and MIL-101(Fe) systems, respectively. The mechanism study proved that the enhanced photocatalytic performance of NQML was resulted from the visible light up-conversion property, electron-hole separation and transfer capacity of NCQDs. Meanwhile, NQML could not only produce h+ but also lead to in-situ generation of O2- and H2O2 by activation of O2 under visible light. The generated H2O2 could react with Fe(II) in MIL-101(Fe) to produce OH so as to construct a dual effect of photocatalysis and photo-Fenton in TC removal.

Dual-excitation regulated Tm3+ upconverting luminescence towards novel encrypted information transmission

Tm3+, capable of emitting blue upconversion luminescence, is generally excited by a single laser source. In this contribution, we design a dual-excitation strategy, using excitation at 800 and 980 nm simultaneously, to manipulate the upconversion properties of Tm3+. It is found that this dual-excitation strategy can enhance the upconversion intensity of Tm3+/Yb3+ codoped β-NaYF4 nanocrystals, which can be used to sensitize the solar cells. More importantly, this strategy also alters the intensity ratio of the two blue emission bands, but can maintain similar emission brightness and color. The mechanisms of dual-excitation strategy are investigated on the basis of spectroscopic observations. Finally, as a proof of concept, the encrypted information transmission based on the dual-excitation strategy is demonstrated.

The role of chelating agent on the structure and up-conversion property of NaLuF4:Yb,Tm as security ink phosphor

Purpose This study aims to investigate the effect of trisodium nitrilotriacetic acid (NTA) on the physical and luminescence emission properties of NaLuF4:Yb, Tm Upconversion (UC) particles and compared with trisodium citrate (CA). Upconversion materials have been remarkably considered in many applications in the past decades. However, the morphology of the UC particles affects their emission properties, depending on the synthesis situation. Design/methodology/approach The UC particles were synthesized by the hydrothermal method. Properties such as crystal phase, particle morphology, particle size, smoothness and uniformity of particle surface and their emission intensity in the UV–Vis region were studied. Findings Observations showed that pH is an essential factor in determining the crystalline phase. In addition, quality factors affect the morphology, particle size and surface smoothness of crystalline facets. It was also found that the UC particles synthesized in the presence of trisodium NTA have a much higher emission intensity than those synthesized in the presence of CA. The use of UC particles in security inks to maintain the brand was also investigated. Originality/value To the best of the authors’ knowledge, for the first time, the effect of trisodium NTA as a chelating agent was investigated on morphology and UC intensity of NaLuF4:Yb,Tm phosphor.

Up-conversion properties of Yb,Tb:YAG single crystals grown by the micro-pulling-down method

Yb,Tb:YAG crystals with various Yb3+ and Tb3+ concentration were grown by the micro-pulling-down method (μ-PD). The absorption spectra, fluorescence spectra and fluorescence decay curves of Yb,Tb:YAG crystals were measured at room temperature. Under 980 nm excitation, Yb,Tb:YAG crystals exhibited intense visible up-conversion luminescence due to the cooperative energy transfer from two Yb3+ ions to one Tb3+ ion. Under 485 nm excitation, Yb,Tb:YAG crystals yielded near-infrared down-conversion emission, ascribing to the cooperative absorption of pumping photons and cooperative energy transfer from one Tb3+ ion to two Yb3+ ions. The energy transfer processes from Yb3+ ions to Tb3+ ions were discussed, and the energy transfer efficiency was calculated. Based on studies of the obtained results, Yb3+/Tb3+ co-doped YAG crystal shows promising potential for sensing, volumetric displays, optical data storage, light emitting diodes.

Enhancement of Red Upconversion Emission of ZnS: Er3+/Yb3+ Powders Synthesized via Solid Phase Reaction Method by Introducing Metal Fluoride

AbstractZnS: Er3+/Yb3+ powders were synthesized by a common solid phase reaction method with NaF, CaF2, LiF, AlF3 and MgF2 as dopant. The enhancement mechanisms of different metal fluorides (NaF, CaF2, LiF, AlF3 and MgF2) and concentrations (0 wt% ∼9 wt %) on structure, morphology and optical properties of ZnS: Er3+/Yb3+ powders were investigated systematically. The results revealed that as synthesized ZnS: Er3+/Yb3+ powders are main exhibited as wurtzite phase, the lattice constant, unit cell volume and lattice strain increase with metal fluoride codoping, which indicates the increase of resultant distortion. As synthesized ZnS: Er3+/Yb3+ powders have an intense red upconversion emission centered at 663 nm and a weak green upconversion emission centered at 567 nm under the excitation of a 980 nm laser diode. Compared with ZnS: Er3+/Yb3+ powders synthesized without metal fluoride, the upconversion emission intensities of ZnS: Er3+/Yb3+ powders synthesized with LiF, NaF, MgF2, AlF3 and CaF enhance ∼12 times, ∼9 times, ∼5 times, ∼3 times and ∼3 times, respectively. The strong red upconversion properties make the ZnS: Er3+/Yb3+ powders synthesized with metal fluoride a potential application in the field of light emitting diodes.

Carbon dots based photocatalysis for environmental applications

Carbon quantum dots (CQDs) have attracted intensive interest in the scientific community attributed to their quantum effect, non-toxicity, fluorescence, photoluminescence, and up-conversion properties, and have been extensively applied in sensing, biomedical, optoelectronic and catalysis fields. Especially, CQDs can act as photocatalysts and be used in energy and environmental areas, such as wastewater remediation and solar energy conversion to fuels and green chemicals. This review will briefly introduce the unique physicochemical properties of CQDs, such as light absorption, photoluminescence, and up-conversion luminescence. The advanced fabrication methods and modification strategies of CQDs will also be summarized. Finally, we will show the broad applications of CQDs in photocatalytic pollutant removal and hydrogen/hydrogen-peroxide production, discussing the structure-activity relationship of CQDs and their complexes in the field of catalysis. Lastly, the key issues and perspectives for future energy and environmental applications are presented. This comprehensive review will provide new insight and inspiration in the synthesis, improvement, and photocatalytic application of CQDs.

Rare-Earth Doped GdVO<sub>4</sub> by Sol-Gel Method: Structural and Luminescence Properties

Rare earths have been extensively developed in recent years, however, new hosts allow high excitation and emission efficiency, in this sense, gadolinium vanadate has been extensively studied and in previous works it has been widely used in down conversion systems. Because of the strong absorption of the VO4 groups and efficient energy transfer from GdVO4 to lanthanide ions, in this work its up-conversion properties were studied when is co-doped with Yb3+, X3+ where X = Tm, Er and Ho. The powders synthesized presented a high crystallinity and a rounded morphology and exhibit a high luminescence when are excited with IR radiation.

Upconversion Properties of Er, Yb Co-Doped Kbi(Moo4)2 Nanomaterials for Optical Thermometry

Upconversion Properties of Er, Yb Co-Doped Kbi(Moo4)2 Nanomaterials for Optical Thermometry

Enhanced selective adsorption and photocatalytic of Ag/Bi2O3 heterostructures modified up-conversion nanoparticles

The degradation of organic pollutant by photocatalytic technology is an emerging and effective approach to purify water resources. Herein, we reported a heterostructure with selective adsorption and photocatalysis for the efficient removal of organic pollutant. The photocatalyst was comprised of up-converting nanoparticle (UCNP) coated with Ag/Bi2O3. The specific crystallinity of Bi2O3 facilitated the selective adsorption of organic molecules with negative polarity, Ag nanoparticles loaded on Bi2O3 promoted the visible light absorption, and the up-conversion property of UCNP turned near-infrared light into ultraviolet and visible light improving further light-harvesting efficiency in the whole solar spectrum. The adsorption process for organic pollutants over Ag/UCNP@Bi2O3 obeyed the pseudo-second-order and the Langmuir isotherm models, and the maximum Langmuir adsorption capacity for tetracycline reached to 717.4 mg/g at pH 7. Meanwhile, the photocatalytic degradation rate of Ag/UCNP@Bi2O3 for tetracycline (100 mg/L) achieved to 0.0037 min−1 under Xenon lamp irradiation after the adsorption equilibrium. This study provided a feasible strategy to develop photocatalysts with efficient adsorption and photocatalytic ability for organic pollutant from water.

An anhydrous precursor approach to BaYF5-based upconverting nanocrystals

With an objective to have easy access to high quality BaYF5 matrix, we report here new anhydrous precursors of barium and yttrium which show a good compatibility in terms of co-thermal decomposition. These complexes not only fill the void of precursors for Ba-based upconverting (UC) nanomaterials but also provide a way to minimize the –OH concentration around these nanocrystals (NCs) to enhance their UC efficiency without requiring the usual core-shell structure. The precursors and the BaYF5 NCs co-doped with Yb3+/Tm3+ ions were thoroughly characterized. The NCs were studied for upconversion properties and preliminary results are presented here. On the basis of these results, a mechanism for the energy transfer in Yb–Tm system is proposed.

Rare earth smart nanomaterials for bone tissue engineering and implantology: Advances, challenges, and prospects.

Bone grafts or prosthetic implant designing for clinical application is challenging due to the complexity of integrated physiological processes. The revolutionary advances of nanotechnology in the biomaterial field expedite and endorse the current unresolved complexity in functional bone graft and implant design. Rare earth (RE) materials are emerging biomaterials in tissue engineering due to their unique biocompatibility, fluorescence upconversion, antimicrobial, antioxidants, and anti‐inflammatory properties. Researchers have developed various RE smart nano‐biomaterials for bone tissue engineering and implantology applications in the past two decades. Furthermore, researchers have explored the molecular mechanisms of RE material‐mediated tissue regeneration. Recent advances in biomedical applications of micro or nano‐scale RE materials have provided a foundation for developing novel, cost‐effective bone tissue engineering strategies. This review attempted to provide an overview of RE nanomaterials' technological innovations in bone tissue engineering and implantology and summarized the osteogenic, angiogenic, immunomodulatory, antioxidant, in vivo bone tissue imaging, and antimicrobial properties of various RE nanomaterials, as well as the molecular mechanisms involved in these biological events. Further, we extend to discuss the challenges and prospects of RE smart nano‐biomaterials in the field of bone tissue engineering and implantology.

Upconversion graphene quantum dots incorporation in performance enhancement of p-i-n perovskite solar cells

Photon upconversion with the potential to reduce spectral mismatch losses is a promising approach in improving solar cell performance. Utilizing the synergistic effect of quantum dots (QDs) along with upconversion (UC) properties in perovskite solar cells (PSCs) is an efficient strategy to extend the absorption spectrum from visible into near-infrared (NIR) range, which leads to an explosive evolution in improving solar cell performance. Herein, upconversion graphene quantum dots (UC GQDs, with the ~4.5 nm particle size) are used to design an improved PSC. UC GQDs are incorporated into p-i-n PSCs by adopting interlayers, next to the hole transport layer (HTL), perovskite, and rear (Au) electrode, as HTL/UC GQD/PSK, PSK/ UC GQD/ETL, ETL/UC GQD/Au structure respectively. The designed CuI/PSK/UC GQD/PCBM/Au p-i-n PSC, by expanding the absorption range from near-infrared (NIF) photons into a visible region, increasing the light-harvesting capability following GQDs, and the suppression of charge recombination processes following a passive effect have shown an effective role in improving p-i-n PSCs performance. These subtly PSCs resulted in a high-power conversion efficiency (PCE) of 19.79% (18.06 ± 1.73) compared to (15.07%, 14.97 ± 0.10) pristine PSCs. The attractive hydrophobic property of the UC GQD has led to an increase in the long-term stability of the resulting solar cell under harsh environmental conditions.