Enhancing Upconversion Research Articles

Enhancing Upconversion Performance via Thermoplasmonic Remote Heating and Its Application to All-Photonic Logic Gates

Enhancing Upconversion Performance via Thermoplasmonic Remote Heating and Its Application to All-Photonic Logic Gates

Enhancing Upconversion Efficiency of Organic Near Infrared Upconversion Devices Based on Inverted Phosphorescent OLEDs as Emitters by Introducing Connecting Layer

Enhancing Upconversion Efficiency of Organic Near Infrared Upconversion Devices Based on Inverted Phosphorescent OLEDs as Emitters by Introducing Connecting Layer

Enhancing Up-Conversion Luminescence Using Dielectric Metasurfaces: Role of the Quality Factor of Resonance at a Pumping Wavelength.

Photonic applications of up-conversion luminescence (UCL) suffer from poor external quantum yield owing to a low absorption cross-section of UCL nanoparticles (UCNPs) doped with lanthanide ions. In this regard, plasmonic nanostructures have been proposed for enhancing UCL intensity through strong electromagnetic local-field enhancement; however, their intrinsic ohmic loss opens additional nonradiative decay channels. Herein, we demonstrate that dielectric metasurfaces can overcome this disadvantage. A periodic array of amorphous-silicon nanodisks serves as a metasurface on which a layer of UCNPs is self-assembled. Sharp resonances supported by the metasurface overlap the absorption wavelength (λ = 980 nm) of UCNPs to excite them, resulting in the enhancement of UCL intensity. We further sharpen the resonances through rapid thermal annealing (RTA) of the metasurface, crystallizing silicon to reduce intrinsic optical losses. By optimizing the RTA condition (at 1000 °C for 20 min in N2/H2 (3 vol %) atmosphere), the resonance quality factor improves from 17.2 to 32.9, accompanied by an increase in the enhancement factor of the UCL intensity from 86- to over 600-fold. Moreover, a reduction in the intrinsic optical losses mitigates the UCL thermal quenching under a high excitation density. These findings provide a strategy for increasing light-matter interactions in nanophotonic composite systems and promote UCNP applications.

Enhancing upconversion luminescence of rare earth ions by the activation of the antenna effect in plasmonic cuprous sulfide nanoparticles

To modulate the local electromagnetic field in the upconversion luminescence (UCL) of rare earth ions is one of the most effective ways to improve the luminescence intensity of upconversion nanocrystals (UCNs). Herein, the luminescence intensity of UCNs was increased by 5.8 times by activating the antenna effect of near-infrared plasma in cuprous sulfide nanoparticles. By simulating the local electromagnetic field distribution of the core-shell composites under 980 nm excitation light, the UCL enhancement mechanism of rare earth ions was studied. It showed that the antenna effect of plasmonic cuprous sulfide nanoparticles enhanced the absorption and utilization of excited light by UCNs, and the optical field in the vicinity of the core-shell composites was significantly optimized by inducing the localized surface plasmon resonance coupling between cuprous sulfide nanoparticles. Finally, our results provide a novel way to effectively regulate the local electromagnetic field in the UCL of rare earth ions.

Enhancing upconversion of Sc2Mo3O12:Yb/Ln (Ln = Er, Ho) phosphors by doping Ca2+ ions

Lanthanide doped Sc2(MoO4)3 upconversion (UC) crystals showed distinct negative thermal quenching effect, which show promising applications in the temperature sensing field. However, it is still valuable to develop novel routes to enhance the room temperature UC intensity. Herein, the UC intensity of the Yb/Er (Ho) doped Sc2Mo3O12 crystals were significantly enhanced by doping Ca2+ ions. The incorporation of Ca2+ ions can break the crystal symmetry around the activators and then promote the 4f-4f transitions followed by the enhanced UC. Especially, the UC intensity of the Sc2Mo3O12:20Yb/1Ho/20Ca was about 100 times than that of Sc2Mo3O12:20Yb/1Ho phosphors. Furthermore, the thermally couple levels based temperature sensing performance was improved after doping Ca2+ ions. Our results may promote the exploration of novel scheelite structural compounds with superior UC properties.

Simultaneous enhancement upconversion luminescence and photocatalytic properties of BiOBr:Yb3+, Er3+ nanosheets by optically inert ions doping

Lanthanide-doped upconversion (UC) materials are important in near-infrared (NIR) photocatalytic field because they can harvest NIR photons and then emit high-energy UV and visible light via the UC process. However, these materials still exhibit low UC luminescence efficiency, which strongly limits their practical applications. Herein, we report UC luminescence enhancement in BiOBr: Yb3+, Er3+ (BYE) nanosheets by doping Li+ and Zn2+ and the elucidation of the enhancement mechanism. The XRD and Rietveld refinement results showed that the doping improved the crystallinity of the samples, with the effect of codoping being more pronounced than that of single doping. Under 980-nm laser excitation, the red emission of the Li+-Zn2+-codoped BYE sample increased drastically by 2.5, 4.3, and 5.3 times than that of the Li+-doped BYE, Zn2+-doped BYE, and BYE samples, respectively. The luminescence enhancement could be ascribed to the reduction of the crystal site symmetry and the improvement of the crystallinity upon Li+ and Zn2+ doping. Moreover, photocatalytic experiments showed that Li+ and Zn2+ doped BYE exhibited better photocatalytic performance than BYE, thus paving the way toward achieving enhanced UC luminescence efficiency.

Enhancing upconversion via constructing local energy clusters in lanthanide-doped fluoride nanoparticles

By introducing local energy clusters within the NaGdF4 lattice, the optimal Er3+, Ho3+ and Tm3+ doping concentrations were increased to 8, 8, and 2 mol%, respectively. The UC intensity was enhanced approximately 54.3 times by doping Ca2+.

Dual-resonance enhancement upconversion luminescence by elongated Ag semi-shell coated on NaYF4:Yb,Er@SiO2 nanorod

Plasmonic resonance induced by metallic structures is a feasible solution to enhance the upconversion luminescence (UCL) of lanthanide-doped nanocrystals. A simulation investigation on the optical properties of an elongated Ag semi-shell coated on nanorod is carried out in this paper. Nondegenerate longitudinal and radial void modes in the Ag cavity can be tuned almost independently and controllably to resonate with excitation and emission simultaneously via adjusting the length and diameter of the nanorod respectively. Moreover, both mode volumes are concentrated in the central region of the cavity. Spectral-plus spatial-overlapping ensures that the elongated Ag semi-shell is an efficient dual-resonance enhancement plasmonic structure. Under dual-resonance conditions, green UCL can achieve 718-fold enhancement when radial resonance overlapping with green UCL, while red UCL can achieve 141-fold enhancement when overlapping with red UCL, with original quantum efficiency (η0) of 1%, both values are higher than that of gold nanorod. Since Purcell effect, resonating with different emission bands can realize color modulation, the intensity ratio of green UCL to red can raise to 9.1 or lower to 1.1 from the original 2.0. Although enhancement gradually weakens with the increase of η0, more than 20-fold enhancement can be still obtained even with η0 up to 33%.

Exploration of up-conversion thermal enhancement mechanism and application on temperature sensing of Sc2W3O12: Yb3+, Er3+ materials

The temperature quenching luminescence effect of optical materials used for fluorescence intensity ratio temperature sensing seriously hinders the realization of temperature sensing in the high temperature region. In recent years, some abnormal thermal enhancement up-conversion materials have attracted extensive attention due to their great potential to sense temperature in high temperature regions. At present, few up-conversion luminescence thermal enhancement materials have reported, and the exploration of thermal enhancement luminescence mechanism is not thorough enough. In this work, new up-conversion luminescence materials Sc2W3O12: Yb3+, Er3+ were prepared, and the thermal enhancement effect was successfully regulated by changing the Yb3+ concentration. The integral emission intensity and intensity of 521 nm at 753 K of Sc1.42W3O12: 0.54Yb3+, 0.04Er3+ can reach 74.5 and 104.9 times of that at room temperature, respectively. In addition, the thermal enhancement luminescence property of up-conversion materials Sc2W3O12: Yb3+, Er3+ was confirmed to be derived from negative thermal expansion properties based on two reference experiments. Finally, the dual temperature sensing model was established to sense the temperature. The results show that the up-conversion thermal enhancement luminescence material is a potential temperature sensing material with high sensitivity, wide temperature sensing range, high resolution and good thermal fatigue resistance.

Surface crystallization enhanced upconversion luminescence in NaGdF4:Yb,Er@NaYF4 core/shell nanocrystals

Coating upconversion nanocrystals with an inert shell for removing surface defects is confirmed to be an efficient way for remarkably enhancing upconversion luminescence. However, it is not clear whether surface atomic structures on the outer inert shell affect upconversion luminescence of active cores. Here, we improved the surface crystallinity of NaGdF4:Yb,Er@NaYF4 active-core/inert-shell nanocrystals using ultrasonic oscillation. It was observed that surface crystallization of the inert shell could lead to an obvious enhancement in upconversion luminescence. The improved surface crystallinity has no obvious influence on the electronic transition in upconversion luminescence processes, but decrease the scattering and absorption to excitation and emission photons. This result clearly indicates that surface crystallization of the inert shell is a powerful route for further enhancing upconversion luminescence besides of the concept of core/shell structure.

Funneling and Enhancing Upconversion Emission by Light-Harvesting Molecular Wires.

Triplet-triplet annihilation (TTA) upconversion has shown promising potentials in the augmentation of solar energy conversion. However, challenging issues exist in improving TTA upconversion efficiencies in solid-states, one of which is the back energy transfer from upconverted singlet annihilators to sensitizers, resulting in decreasing upconversion emission. Here we present a light-harvesting molecular wire consisting of dendrons with 9,10-diphenylanthracene derivatives (DPAEH) at the periphery and p-phenylene ethynylene oligomers (PPE) as the wire core. The peripheral DPAEH antenna funnels singlet excitonic energy to the wire on a 12 ps time scale. Incorporating the molecular wire into the TTA upconversion solid consisting of the DPAEH annihilator and the porphyrin sensitizer evidently improves the upconversion quantum yield from 1.5% to 2.7% upon 532 nm excitation by suppressing the back energy transfer from the singlet annihilator to the sensitizer. This finding offers a potential route to use a singlet energy light-harvesting architecture for enhancing TTA upconversion.

Enhancing upconversion of Nd3+ through Yb3+-mediated energy cycling towards temperature sensing

Photon upconversion of lanthanides has been a powerful means to convert low-energy photons into high-energy ones. However, in contrast to the mostly investigated lanthanide ions, it has remained a challenge for the efficient upconversion of Nd3+ due to the deleterious concentration quenching effect. Here we report an efficient strategy to enhance the upconversion of Nd3+ through the Yb3+-mediated energy cycling in a core-shell-shell nanostructure. Both Nd3+ and Yb3+ are confined in the interlayer, and the presence of Yb3+ in the Nd-sublattice provides a more matched energy for the upconversion transitions occurring at the intermediate state of Nd3+ towards much better population at its emissive levels. Moreover, this design also minimizes the possible cross-relaxation processes at both intermediate level and the emissive levels of Nd3+ which are the primary factors limiting the upconversion performance for the Nd3+-doped materials. Such energy cycling-enhanced upconversion shows promise in temperature sensing.

Enhancing upconversion of manganese through spatial control of energy migration for multi-level anti-counterfeiting.

The upconversion of manganese (Mn2+) exhibits a green light output with a much longer lifetime than that of lanthanide ions, showing great potential in the frontier applications like information security and anti-counterfeiting. Mn2+ can be activated by energy migration upconversion. However, there exists serious quenching interactions between Mn2+ and the lanthanides at the core-shell interfacial area, which would markedly reduce the role of Tm3+ as a ladder to facilitate the up-transition and subsequently limit the upconversion of Mn2+. Here, we propose a mechanistic strategy to enhance the upconversion luminescence of Mn2+ by spatial control of energy migration among Gd sublattice through introducing an additional migratory NaGdF4 interlayer within the commonly used core-shell nanostructure. This design can not only isolate the interfacial quenching interactions between the sensitized core and luminescent shell, but also allow an efficient channel for energy transport, resulting in enhanced upconversion of Mn2+. Moreover, the relatively long lifetime of Mn2+ (around 32.861 ms) provides new possibilities to utilize the temporal characteristic for the frontier application of multi-level anti-counterfeiting through combining the time-gating technology.

Enhancing upconversion emissions and temperature sensing properties by incorporating Mn2+ for KLu2F7:Yb3+/Er3+ nanocrystals based on thermally and non-thermally coupled levels

Pure phase KLu2F7:Yb3+/Er3+/Mn2+ nanocrystals were obtained for which the temperature sensitivity reached up to 45.11 × 10−3 K−1 employing non-thermally coupled levels.

Enhancing upconversion emission of Er3+ in single β-NaYF4 microrod through constructing different inert and active shells with doping Yb3+ ions

The construction of core-shell structure helps in enhancing upconversion luminescence in lanthanide-doped micro/nanomaterials. This study aimed to synthesize a series of NaYF4 and NaErF4 core-shell microrods based on epitaxial growth technology so as to enhance the upconversion emission. The upconversion luminescence properties of single NaYF4:Yb3+/Er3+ and NaErF4 microrods with different core-shell structures were carefully studied using a confocal microscope spectroscopy test system under 980-nm near-infrared excitation. The upconversion emission intensity and red-to-green emission intensity ratio of Er3+ ions were remarkably enhanced in different single microrods by building different inert and active core-shell structures. The higher red-to-green ratio was mainly due to the cross-relaxation between Er3+ ions and the energy back-transfer process from Er3+ to Yb3+ ions, which were explained on the basis of spectral characteristics and rate equations. These tunable NaYF4 and NaErF4 core-shell microrods had the potential to be applied to displays, micro-lasers, and anti-counterfeiting.

Enhancing upconversion emission and temperature sensing modulation of the La2(MoO4)3: Er3+, Yb3+ phosphor by adding alkali metal ions

Trivalent Er3+-doped La2(MoO4)3 upconversion phosphors with intense green emmision were synthesized at 800 °C by the solid-state reaction route, promoting the development of novel optical thermometry. The color emitted from the samples was minorly affected by the excitation power and doping concentration. Yb3+ is a better sensitizer for the La2(MoO4)3: Er3+ phosphor and it can enhance the emission intensity when a certain amount is co-doping in the system. The up-conversion luminescent mechanism was investigated using the pump power-dependent UC emission spectra. Alkali metal doping increased the up-conversion emission intensities drastically, and Li+ ions can enhance the luminous intensity by more than 20 times. The fluorescence intensity ratio of the transition emission 2H11/2-4I15/2 and 4S3/2-4I15/2 was used to study upconversion optical temperature sensing. The sensitivity changes from doping with diverse alkali metal ions and their effects on the optimal temperature range are discussed in detail. Alkali metal ions doping extended the temperature range, indicating that this phosphor is a potential candidate for temperature-sensing probes.

Enhancing upconversion photoluminescence by plasmonic-photonic hybrid mode.

Upconversion photoluminescence (UCPL) of rare-earth ions has attracted much attention due to its potential application in cell labeling, anti-fake printing, display, solar cell and so forth. In spite of high internal quantum yield, they suffer from very low external quantum yield due to poor absorption cross-section of rare-earth ions. In the present work, to increase the absorption by rare earth ions, we place the emitter layer on a diffractive array of Al nanocylinders. The array is designed to trap the near infrared light in the emitter layer via excitation of the plasmonic-photonic hybrid mode, a collective resonance of localized surface plasmons in nanocylinders via diffractive coupling. The trapped near-infrared light is absorbed by the emitter, and consequently the intensity of UCPL increases. In sharp contrast to the pure localized surface plasmons which are bound to the surface, the hybridization with diffraction allows the mode to extend into the layer, and the enhancement up to 9 times is achieved for the layer with 5.7 µm thick. This result explicitly demonstrates that coupling the excitation light to plasmonic-photonic hybrid modes is a sensible strategy to enhance UCPL from a thick layer.

Enhancing upconversion luminescence of highly doped lanthanide nanoparticles through phase transition delay

Doping of rare earth (RE) ions in a low-phonon-energy host matrix is an effective strategy to enhance the upconversion luminescence (UCL) of lanthanide-doped nanoparticles. However, doping of optically inactive RE ions at high concentrations can cause an undesirable phase transition of the host matrix, with concomitant decrease in luminescence. Herein, we present a phase-transition-delay protocol to effectively preserve the pure orthorhombic phase of a KLu2F7:Yb3+,Er3+ system, even at high RE dopant concentrations. The proposed concept can be realized by incorporating a set of optically inactive RE dopants, i.e., Y3+ or Gd3+, with different ionic radii to replace the Lu3+ ions in the host matrix to overcome the energy barrier of the phase transition. The nanoparticles were synthesized in a high-boiling solvent or at a high reaction temperature. We observed maximal UCL of Er3+ at different Y3+ or Gd3+ dopant concentrations; the optimal Y3+ or Gd3+ concentration at which maximal UCL is observed is 10 mol% for samples prepared by a water-based hydrothermal route, while it is 30 mol% for samples prepared by an oleic acid-based hydrothermal route. Further, this optimal concentration could be increased to as much as 50 mol% by adopting a high reaction temperature. The high doping of Y3+ or Gd3+ can efficiently lead to enhanced upconversion performance of the final materials (as much as 32-fold and 9-fold enhancements in the upconversion intensity and quantum yield, respectively, are achieved). The UCL enhancement is caused by the break-down of the symmetry of lanthanide sites in the crystal lattice induced by Y3+ or Gd3+, which enhances the energy transfer probabilities between Yb3+ and Er3+. Our findings highlight a convenient route to simultaneously tune the phase transition of the host and upconversion output, and this strategy can be applied to other upconversion host materials.

Enhanced upconversion and near-infrared emissions of co-doped Ho3+/Yb3+ in TeO2–ZnO–Na2CO3–La2O3 tellurite glasses

TeO2–ZnO–Na2CO3–La2O3 (TZNL) tellurite glasses were prepared using a conventional melt-quenching method. The effects of the Mn2+ ions and (Yb3+–Mn2+–Mn2+) trimer on the enhancement upconversion (UC) and near-infrared (NIR) emissions intensity of the co-doped Ho3+/Yb3+ bands in TZNL tellurite glasses were investigated. With the formation of the (Yb3+–Mn2+–Mn2+) trimer and the energy transfer (ET) from Mn2+ and (Yb3+–Mn2+–Mn2+) trimer into Ho3+, the UC/NIR emissions intensity of the co-doped Ho3+/Yb3+ bands was significantly increased. In addition, the ET processes between the Mn2+ and (Yb3+–Mn2+–Mn2+) trimer with Ho3+ were shown.

Enhancement of upconversion, temperature sensing and cathodoluminescence in the K+/Na+ compensated CaMoO4:Er3+/Yb3+ nanophosphor

Enhancing upconversion, temperature sensing and cathodoluminescence in the CaMoO4:Er3+/Yb3+ nanophosphor via K+/Na+ simultaneous codoping.