Upconversion in NaYF 4 :Yb, Er nanoparticles amplified by metal nanostructures (original) (raw)
Related papers
Optics Express, 2018
The up-conversion process is extensively studied because of its wide variety of applications such as bioimaging, energy harvesting, and optical sensors. However, the optical conversion efficiency is still relatively low and needs to be improved. Therefore, this paper introduces a detailed study of improving the up-conversion emission efficiency through adding plasmonic metallic nanostructures to the up-conversion optical centers. Our idea is to couple the optical plasmonic resonance with the visible emission of the optical centers under IR excitation. The optical centers are erbium ions hosted by fluoride low-phonon environment. Our calculations consider most possible transitions that can occur between the optical centers; tri-valent erbium ions, through Judd-Ofelt analysis. In addition, the effect of changing some parametric values is discussed, such as irradiance, and multi-phonon relaxations, to show their optimum values which correspond to best quantum yield efficiency. By increasing the diameter of added gold nanoparticles (Au NPs), the probability of occupation has been increased, and consequently, both the luminescence and up-conversion efficiency have been increased.
The Journal of Physical Chemistry C, 2014
Size-dependent quantum confinement has important effects on the energy transfer and radiative and nonradiative transitions in nanophosphors. For lanthanidedoped nanoparticles, the confinement effect is induced mostly via electron−phonon interaction, and analysis of temperaturedependent spectroscopic properties provides an effective method for disclosing its underlying mechanism. Herein, an intriguing and unprecedented enhancement of the upconversion luminescence (UCL) at higher temperatures in hexagonalphase NaYF 4 :Yb 3+ , Er 3+ upconversion nanoparticles (UCNPs) is reported. Moreover, this anomalous UCL enhancement shows a strong dependence on the particle size and becomes more significant for UCNPs with a smaller size. This anomalous thermal behavior is interpreted on the basis of phonon-assisted energy transfer and phonon confinement effect. The findings are relevant to the engineering of the nanostructures of UCNPs and to the further understanding of the UCL mechanism.
2013
Despite recent achievements to reduce surface quenching in NaYF 4 :Yb,Er nanocrystals, a complete understanding of how the nanocrystal size affects the brightness of upconversion luminescence is still incomplete. Here we investigated upconversion luminescence of Yb,Er-doped nanocrystals in a broad range of sizes from 6 nm to 45 nm (cubic or hexagonal phases), displaying an increasing red-to-green luminescence intensity ratio and reduced luminescence lifetimes with decreasing size. By analyzing the upconversion process with a set of rate equations, we found that their asymptotic analytic solutions explain lower decay rates of red compared to green upconversion luminescence. Furthermore, we quantified the effect of the surface on luminescence lifetime in a model where nanocrystal emitters are divided between the near-surface and inside regions of each nanocrystal. We clarify the influence of the four nonradiative recombination mechanisms (intrinsic phonon modes, vibration energy of surface ligands, solvent-mediated quenching, and surface defects) on the decay rates for different-size nanocrystals, and find that the defect density dominates decay rates for small (below 15 nm) nanocrystals. Our results indicate that a defect-reduction strategy is a key step in producing small upconversion nanocrystals with increased brightness for a variety of bioimaging and biosensing applications. † Electronic supplementary information (ESI) available: Additional information for size distribution histograms , upconversion power-dependence gradients ), upconversion luminescence decay in different surroundings , and rate equations for Yb,Er-doped nanocrystals and the asymptotic solutions are available. See
Journal of Luminescence, 2007
The improvement in the upconversion (UC) luminescence due to the surface plasmonic properties of precious metals is an effective mode to increase UC luminescence efficiency. In the present research work, pure hexagonal-phase NaYF 4 : Yb, Er UC nanocrystals were prepared via a reverse micro emulsion method. A single-step method was adopted to change the hydrophobic surfaces of the as-prepared NaYF4: Yb, Er nanocrystals. After the surface modification, Au/Ag nanoparticles were decorated on the surfaces of NaYF4:Yb, Er nanocrystals. The structural analysis and composition of the nanocomposites were studied in details. The XRD pattern indicated the formation of the hexagonal structure of NaYF 4 crystals. The decorated UC nanocrystals exhibited a prominent UC emission in green and red bands under 980 nm laser excitation due to normal two-photon UC process. The UC intensity increased by ∼3 times than the uncoated samples. The enhancement mechanism of UC luminescence was investigated in details.
Zenodo (CERN European Organization for Nuclear Research), 2021
The dopant concentration of lanthanide ions in photon-upconversion nanoparticles (UCNPs) remains one of the key points to boost these nanomaterials' brightness and, therefore, their application development. Here, we analyzed the effect of Er 3+ and Yb 3+ dopant concentration of β-NaYF 4 :Yb 3+ ,Er 3+ nanoparticles on the visible upconversion and near-infrared downconversion luminescence intensity. To maintain the size and the morphological properties of the nanoparticles we used a total dopant concentration of 22% while varying the ratio of Yb 3+ to Er 3+ ions from 0 to 10. A huge increase in luminescence takes place as the Yb/Er ratio increases following a power-law behavior, being this luminescence enhancement greater at low excitation intensities. Above an Yb/Er ratio around two, saturation occurs with a slight peak when this ratio is around four. Simulations using a rate equation model showed that upconversion luminescence (UCL) is mainly produced by energy transfer between neighboring Er 3+ ions at low Yb/Er ratios, while at high ratios, energy transfer from Yb 3+ to Er 3+ ions dominates. However, downconversion luminescence (DCL) is produced at all analyzed ratios, except 0, by this last mechanism.
Optics Letters, 2014
In this work, we report on efficient visible and near-IR upconversion emissions in colloidal hexagonal-phase core/ shell NaYF 4 :Er 3 ∕NaYF 4 nanoparticles (∼38 nm) under IR laser excitation at 1523 nm. Varying amounts of Er 3 dopants were introduced into the core NaYF 4 :Er 3 nanoparticles, revealing an optimized Er 3 concentration of 10% for the highest luminescent efficiency. An inert epitaxial shell layer of NaYF 4 grown onto the core of the NaYF 4 :Er 3 10% nanoparticle increased its upconversion emission intensity fivefold due to suppression of surface-related quenching mechanisms, yielding the absolute upconversion efficiency to be as high as ∼3.9 0.3% under an excitation density of 18 W∕cm 2. The dependence of the intensity of upconversion emission peaks on laser excitation density in the core/shell nanoparticle displayed "saturation effects" at low excitation density in the range of 1.5-18 W∕cm 2 , which again demonstrates high upconversion efficiency.
Journal of Electronic Materials, 2016
We propose a new method to prepare Er 3+ /Yb 3+-codoped b-NaYF 4 upconversion nanoluminophores, allowing creation of single-crystalline-phase b-NaYF 4 : Er 3+ /Yb 3+ with concentrations up to 20 mol.% through a hydrothermal process. Using hexagonal-phase Y(OH) 3 precursors with different nanostructures (nanosheets, nanorods, nanotubes, etc.), one can obtain many types of onedimensional nano-NaYF 4 :Er 3+ /Yb 3+ materials and significantly improve the multiphase phenomenon, which is a common challenge facing many research groups that use a hydrothermal process for synthesis of NaYF 4 compounds. Upon near-infrared laser excitation at 976 nm, the obtained b-NaYF 4 :Er 3+ /Yb 3+ nanorods emit in green (2 H 11/2 , 4 S 3/2 fi 4 I 15/2) and red (4 F 9/2 fi 4 I 15/2) spectral regions with high intensity. Moreover, it is shown that one can change the luminescence integrated intensity ratio between the red and green emissions by varying the concentration and components of Er 3+ and Yb 3+ in the NaYF 4 host material. Comparative studies on the luminescence kinetics of the NaYF 4 :Er 3+ / Yb 3+ nanoluminophores were also conducted to explain the influence of Yb 3+ ion on the upconversion processes.
ACS Applied Materials & Interfaces, 2013
Multifunctional materials exhibiting photon upconversion show promising applications for biological imaging and sensing. In this study, we examine the solid-state upconversion emission of NaYF 4 :Yb,Er nanoparticles in the presence of iron oxide nanoparticles. Fe 3 O 4 nanoparticles (6 nm) were mixed with NaYF 4 :Yb,Er nanoparticles (either 10 or 50 nm) in varying proportions by drying chloroform solutions of nanoparticles onto glass slides. Upconversion spectra were acquired, and a laser power-dependent emission was observed and correlated with the iron oxide content in the mixture. Changes in the lattice temperature of the upconverting particles were monitored by careful observation of the relative intensities of the 2 H 11/2 and 4 S 3/2 → 4 I 15/2 transitions. The emission characteristics observed are consistent with an iron oxide-induced thermal effect that is dependent on both the laser power and the proportion of iron oxide. The results highlight that the thermal effects of mixed nanoparticle systems should be considered in the design of luminescent upconverting hybrid materials.
2012
Lanthanide-doped upconversion nanocrystals (UCN) converting low energy photons to high energy photons have emerged as an efficient and versatile bioimaging and therapeutic tool. However, the upconversion efficiency of the UCNs is low, which limits their applications. Plasmonic modulation makes it possible to enhance the luminescence of these nanocrystals. We hypothesize that the enhancement of the upconversion luminescence for all the emission peaks simultaneously could be achieved if the UCNs are coated with a gold nanoshell and the surface plasmon resonance (SPR) peak is tuned to the near-infrared (NIR) region and made resonant with the absorption of the UCNs, thereby substantially increasing the excitation flux via local field enhancement (LFE) effect. Furthermore, the nanoparticles could be used for darkfield imaging due to the light scattering caused by the gold nanoshell. Herein, we report a poly-(amino acid)-templated gold-shell encapsulation of the silica coated NaYF 4 :Yb,Er UCNs and show how a deft tuning of the SPR peak from visible to NIR region dramatically transforms the luminescence quenching into an enhancement effect and how the nanoparticles are used for combined upconversion fluorescence and darkfield light scattering imaging.