Near-infrared Upconversion Research Articles

Blue and near-infrared up-conversion in double-air-cladding Tm3+-doped silica fiber under 1064 nm excitation

Double-air-cladding Tm3+-doped silica fiber with a large core is fabricated by stacking capillaries method. By the excitation at 1064 nm, the optical properties of this fiber doped with 0.1 mol% Tm3+ are studied. The blue and near-infrared emissions around 473 and 793 nm are experimentally observed. In addition, the up-conversion mechanism of Tm3+ in glass is investigated. The results show that the Tm3+-doped fiber with a large core can be used as the potential optical material for the high power fiber laser which operates at the blue and near-infrared wavelengths.

Low-temperature thermometry based on upconversion emission of Ho/Yb-codoped Ba0.77Ca0.23TiO3 ceramics

Ho/Yb-codoped Ba0.77Ca0.23TiO3 ferroelectric ceramics were prepared by a solid-state reaction method. Under the excitation of 980nm, all the samples exhibited strong green, red and near-infrared upconversion emissions. Upconversion emission intensities of the Ho/Yb-codoped Ba0.77Ca0.23TiO3 ferroelectric ceramics can be enhanced with moderate Yb addition. Additionally, optical temperature sensing properties based on the upconversion emissions of the Ba0.77Ca0.23Ti0.975Ho0.005Yb0.03O3 ferroelectric ceramics were also investigated. The result demonstrated that the optical temperature sensor can be operated in the temperature range of 93–300K with a maximum sensitivity of about 0.0053K−1 at 93K. Compared with other rare-earth doped materials, it is much easier and cheaper to synthesize Ho/Yb-codoped Ba0.77Ca0.23TiO3 ferroelectric ceramics.

Multifunctionalities of near-infrared upconversion luminescence, optical temperature sensing and long persistent luminescence in La3Ga5GeO14:Cr3+,Yb3+,Er3+and their potential coupling

The multifunctionalities of near-infrared upconversion luminescence, optical temperature sensing and long persistent luminescence are demonstrated in La3Ga5GeO14:Cr3+,Yb3+,Er3+and their potential coupling are discussed in detail.

Enhanced Near-Infrared Upconversion Emission of Yb3+-Tm3+ Co-doped Gd2O3 Sub-microrods

Lanthanide-doped rare-earth oxides have aroused great interest in display and bio-probe technology due to their excellent luminescent and magnetic performance. In this paper, Gd2O3 sub-microrods (SMRs) with cubic structure are obtained via heat-treatment from gadolinium hydroxides precursor. Upconversion (UC) spectra show intense near-infrared (NIR) emission which is assigned to 3H4 → 3H6 transition of Tm3+. From the double logarithmic plot of emission intensity versus pump powers, it was seen that typical two photons were involved in the NIR UC process. Moreover, a series of Gd2O3:18%Yb3+,x%Tm3+ (x = 0.1, 0.5, 1, 2, 5) and Gd2O3:y%Yb3+,0.5%Tm3+ (y = 1, 5, 10, 40, 80) SMRs were prepared and characterized to explore their NIR emission properties. Finally, the enhanced NIR emission property was found in Gd2O3:Yb3+,Tm3+ SMRs from the reduced NaOH concentration and the reduced calcinations temperatures.

Visible and near-infrared upconversion photoluminescence in lanthanide-doped KLu3F10 nanoparticles

Upconversion (UC) photoluminescent nanocrystals of Ln3+-doped KLu3F10 have been synthesized via a facile and environmentally-friendly hydrothermal route.

Pure and almost pure NIR emission of Tm and Tm,Yb-CeO2 under UV, X-ray and NIR up-conversion excitation: key roles of level selective antenna sensitization and charge-compensation.

Herein, we report on the pure and almost pure near-infrared (NIR) emission at around 807 nm observed for Tm(Yb) (co)-doped CeO2 nanoparticles (NPs) under UV, X-ray and NIR up-conversion excitation. The optical responses are attributed to the low-lying charge-transfer of CeO2 that acts as a selective antenna sensitizer of the Tm (3)H4 emission and Yb doping that lowers the local symmetry at Tm sites and introduces additional phonon modes. Selective antenna sensitization is also observed for Er/Ho (Yb) (co)-doped CeO2 NPs. To the best of our knowledge, this is a first study which correlates the down- and up-conversion emission properties of lanthanide(s)-(co) dopants with the CeO2 structure highlighting also the outstanding potential of these NPs in high-penetration tissue imaging and therapy.

Sub-10 nm lanthanide doped BaLuF5 nanocrystals: Shape controllable synthesis, tunable multicolor emission and enhanced near-infrared upconversion luminescence

In this study, sub-10nm BaLuF5 nanocrystals with cubic phase structure were synthesized by a solvothermal method using oleic acid as the stabilizing agent. The as-prepared BaLuF5 nanocrystals were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and analyzed by the upconversion (UC) spectra. The TEM results reveal that these samples present high uniformity. Compared with Gd-free samples, the size of BaLuF5:Yb/Er doped with 10% Gd3+ decreased to 5.6nm. In addition, BaLuF5:Yb/Tm/Gd upconversion nanoparticles (UCNPs) presented efficient near-infrared (NIR)-NIR UC luminescence. Therefore, it is expected that these ultra-small BaLuF5 nanocrystals with well-controlled shape, size, and UC emission have potential applications in biomedical imaging fields.

Near-infrared to visible and near-infrared upconversion of monoclinic Gd2O3:Yb3+/Tm3+ nanoparticles prepared by laser ablation in liquid for fluorescence imaging

Upconversion nanoparticles (UCNPs) possess great potential for application in fluorescence imaging. Here, the high crystalline Gd2O3:Yb3+/Tm3+ UCNPs with the average diameter of 7.18nm were fabricated by laser ablation in liquid (LAL). Under excitation at 980nm, visible blue fluorescence of the LAL-derived Gd2O3:Yb3+/Tm3+ UCNPs is obtained and can be used for live cells imaging. Meanwhile, more efficient near-infrared (NIR) emission (∼800nm) than the visible fluorescence is observed. The excitation and emission of Gd2O3:Yb3+/Tm3+ UCNPs are both within the “optical transmission window” of biological tissue, capable of great potential for deep tissues imaging.

A bifunctional Cr/Yb/Tm:Ca3Ga2Ge3O12 phosphor with near-infrared long-lasting phosphorescence and upconversion luminescence.

Currently, upconversion nanocrystals and long-lasting phosphorescent particles have attracted extensive research interest for their possible applications as bioimaging probes. However, there are few reports concerning the achievement of both upconversion luminescence of lanthanide ions and long-lasting phosphorescence of transition metal ions in a sole host so far. Herein, we demonstrate a novel calcium gallium germanium garnet (Ca3Ga2Ge3O12) host where lanthanide ions such as Tm(3+)/Yb(3+) and transition metal ions such as Cr(3+) can be easily incorporated through substituting the Ca(2+) and Ga(3+) respectively. This Cr/Yb/Tm:Ca3Ga2Ge3O12 phosphor exhibits both broadband near-infrared long-lasting phosphorescence of Cr(3+) with an afterglow time of more than 7000 s and near-infrared to near-infrared upconversion luminescence of Tm(3+). Impressively, it is evidenced that the addition of Yb(3+)/Tm(3+) into Cr:Ca3Ga2Ge3O12 not only results in Tm(3+) upconversion luminescence but also greatly increases Cr(3+) afterglow time. Based on excitation/emission, three-dimensional thermoluminescence, and time-resolved luminescence spectra, the related long-lasting phosphorescence and upconversion luminescent mechanisms are systematically discussed as well.

Near-infrared upconversion nanoparticles for bio-applications

Upconversion nanoparticles (UCNs) attract intensive attentions in biomedical applications. They have shown great potential in bioimaging, biomolecule detection, drug delivery, photodynamic therapy and cellular molecules interactions. Due to the anti-Stokes optical property and NIR excitation, UCNs overcome the drawbacks encountered in conventional luminescent biomarkers. High signal to noise ratio, low cytotoxicity and stable high throughput results are obtained using UCNs as luminescent labels or light triggers in biomedical applications. In this review article, the reason for choosing UCNs as biomedical agents, the progress of the UCNs development and case studies of their biomedical applications will be discussed.

Anomalous NIR Luminescence in Mn2+‐Doped Fluoride Perovskite Nanocrystals

An anomalous near‐infrared (NIR) upconversion (UC) emission band at approximately 770 nm is demonstrated in KZnF3:Yb3+,Mn2+ nanocrystals with heavy Mn2+ doping. This band would enable advanced biological imaging with improved resolution and enhanced penetration depth. Careful studies based on structure analysis, excitation and emission spectra, and luminescence decay curves indicate that this unusual NIR emission (770 nm) originates from the 6A1g(S)4T1g(G)→6A1g(S)6A1g(S) transitions of the Mn2+–Mn2+ dimers. The influence of Mn2+ concentration and temperature on the Stokes and UC luminescence properties are also investigated. The proposed mechanism for the observed NIR UC emission involves ground state absorption and excited state absorption processes. The present results not only provide a useful and effective approach to achieving pure NIR UC emission, and also new insights into the development of advanced photonic devices and technologies.

NIR to NIR upconversion in KYb2F7: RE3+ (RE = Tm, Er) nanoparticles for biological imaging.

Until recently, many contrast agents widely used in biological imaging have absorbed and emitted in the visible region, limiting their usefulness for deeper tissue imaging. In order to push the boundaries of deep tissue imaging with non-ionizing radiation, contrast agents in the near infrared (NIR) regime, which is not strongly absorbed or scattered by most tissues, are being sought after. Upconverting nanoparticles (UCNPs) are attractive candidates since their upconversion emission is tunable with a very narrow bandwidth and they do not photobleach or blink. The upconversion produced by the nanoparticles can be tailored for NIR to NIR by carefully choosing the lanthanide dopants and dopant ratios such as KYb2F7: RE3+ (RE = Tm, Er). Spectroscopic characterization was done by analyzing absorption, fluorescence, and quantum yield data. In order to study the toxicity of the nanoparticles Monkey Retinal Endothelial Cells (MREC) were cultivated in 24 well plates and then treated with nanoparticles at different concentrations in triplicate to obtain the optimal concentration for in vivo experiments. It will be shown that these UCNPs do not elicit a strong toxic response such as quantum dots and some noble metal nanoparticles. 3-D optical slices of nanoparticle treated fibroblast cells were imaged using a confocal microscope where the nucleus and cytoplasm were stained with DAPI and Alexa Fluor respectively. These results presented support the initial assumption, which suggests that KYb2F7: RE3+ would be excellent candidates for NIR contrast agents.

Enhancement of near-infrared to near-infrared upconversion emission in the CeO_2: Er^3+, Tm^3+, Yb^3+ inverse opals

In this Letter, CeO₂: Er³⁺, Tm³⁺, Yb³⁺ inverse opal with near-infrared to near-infrared upconversion emission was prepared by polystyrene colloidal crystal templates, and the influence of photonic bandgap on the upconversion emission was investigated. Comparing with the reference sample, suppression of the blue or red upconversion luminescence was observed in the inverse opals. It is interesting that the near-infrared upconversion emission located at about 803 nm was enhanced due to the inhibition of visible upconversion emission in the inverse opals. Additionally, the variety of upconversion emission mechanisms was observed and discussed in the CeO₂: Er³⁺, Tm³⁺, Yb³⁺ inverse opals.

Monochromatic Near-Infrared to Near-Infrared Upconversion Nanoparticles for High-Contrast Fluorescence Imaging

To develop a fluorescent bioprobe for high-contrast deep tissue fluorescence imaging, monochromatic 800 nm upconversion emissions based on NaYF4: Yb3+, Tm3+ upconversion nanoparticles are investigated. The ratio of I800 to I470, which is used to describe the monochromaticity, showing exponential growth with the increase of Tm3+ doping concentration in NaYF4: Yb3+, Tm3+ nanoparticles, can reach as high as 757 at 4% Tm3+. At such a doping level, the absolute quantum efficiency can reach 3.9 × 10–3 as measured by a calibrated integrating sphere, which is sufficient for fluorescence imaging. High-contrast fluorescence phantom imaging was obtained by adjusting monochromaticity of 800 nm upconversion emission under the excitation of a 980 nm diode laser.

Monodispersed LaF3 nanocrystals: shape-controllable synthesis, excitation-power-dependent multi-color tuning and intense near-infrared upconversion emission

In this study, monodispersed and high-quality hexagonal phase LaF3 nanocrystals with different shapes and sizes were synthesized by a solvothermal method using oleic acid as the stabilizing agent. The as-prepared LaF3 nanocrystals were characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD), and analysis of the upconversion spectra. The TEM results reveal that the samples present high uniformity and monodispersity and are self-assembled into a two-dimensional ordered array. Moreover, the shape, size and structure of the nanocrystals can be readily tuned by adjusting the NaF content. With increasing content of NaF, the shape of the LaF3 nanocrystals changed from particle to rod and the size gradually increased. More importantly, high NaF content favors the formation of one-dimensional nanorods. High Y b3+ and Er3+ content is beneficial to synthesizing the hexagonal phase of NaLaF4 nanocrystals. Furthermore, the TEM results show that the shape and size of the LaF3 nanocrystals can also be tuned by doping lanthanide ions, which provides a new route for size and shape control of nanocrystals. In addition, LaF3 nanocrystals co-doped with Y b3+/Tm3+ present efficient near-infrared (NIR)–NIR upconversion luminescence. More importantly, the upconversion luminescent colors can be readily tuned from blue-white to blue by adjusting the excitation power. Therefore, it is expected that these LaF3 nanocrystals with well-controlled shape, size and NIR–NIR upconversion emission have potential applications in biomedical imaging fields.

Pure near-infrared to near-infrared upconversion of multifunctional Tm3+ and Yb3+ co-doped NaGd(WO4)2 nanoparticles

Pure near-infrared to near-infrared upconversion and paramagnetism were observed in NaGd(WO4)2:Tm3+,Yb3+ nanoparticles, suggesting that they are promising materials for applications in high-contrast bio-imaging and bio-separation.

Remarkable enhancement of the near-infrared upconversion emission in the β-NaYF4:Yb3+/Tm3+ system with controllable morphology

In this work, β-NaYF4:Yb3+/Tm3+ samples with controllable morphologies have been prepared using a facile hydrothermal method. The overall morphologies of the samples can be adjusted from rod-shape to hexagonal prism-shape with crown-like top end, and then to hexagonal plate-shape by increasing the pH values of initial solutions ranging from 3 to 9. Furthermore, the pH values of the initial solutions show great effect on upconversion emissions of the samples, and it is worth noting that higher both near-infrared emission and chromatic purity are observed for the samples obtained under lower pH values conditions. The corresponding mechanism may be attributed to the combination of more Yb3+ ions incorporated in the lattice and the reduced lattice constants under the condition of lower pH values, favoring energy transfer between Yb3+ and Tm3+ ions or between two neighboring Tm3+ ions.

Blue and near-infrared up-conversion photoluminescence and dielectric relaxation of Tm3+/Yb3+ co-doped (Bi, Y)2Ti2O7 pyrochlore thin films

The blue emission and near-infrared (NIR) up-conversion photoluminescence and dielectric relaxation of Tm3+/Yb3+ co-doped (Bi, Y)2Ti2O7 pyrochlore thin films prepared by a chemical solution deposition method have been investigated. The pyrochlore phase has been maintained for all compositions. Intense blue and NIR emission can be detected on the thin films on fused silica substrates excited by a 980nm diode laser. Three UC emission bands centered at 480nm, 665nm, and 800nm in the spectra can be assigned to 1G4→3H6, 1G4→3F4 and 3H4→3H6 transitions of Tm3+ ions, respectively. The dependence of UC emission intensity on pumping power indicates that the blue emission of the thin films follows a three-photon process while the NIR emission is a two-photon process. The thin films also exhibit a relatively high dielectric constant and a low loss as well as good bias voltage stability. Temperature and frequency dependent dielectric relaxation has been investigated. This study suggests that Tm3+/Yb3+ co-doped (Bi, Y)2Ti2O7 thin films can be applied to new multifunctional photoluminescence dielectric thin-film devices.

Upconversion Emission Properties of Erbium- and Ytterbium-Doped Potassium Lithium Tantalate Niobate Ceramics

We investigate the luminescence properties of erbium-doped and erbium-ytterbium-codoped potassium lithium tantalate niobate ceramics prepared by the solid phase syntheses method. The crystalline structure and surface morphology of these ceramics are tested by x-ray diffraction and scanning electron microscopy. The green, red, and near-infrared upconversion photoluminescence properties are analyzed by the steady-state spectra under 975 nm and 800 nm excitations. These ceramics are well sintered and tetragonal tungsten type crystalline structure with the 4mm point group and the P4bm space group. The Er3+ upconversion emission integrated intensities increase with the increase in Er3+ ion concentration, while the green emission decreases with the increase in Yb3+ ion concentration under the 800 nm excitation. An effective energy back transfer process from the Er3+ 4S3/2 state to Yb3+ ground state plays an important role in enhancing the red emission and weakening the green emission.

Performance enhancement in dye-sensitized solar cells by utilization of a bifunctional layer consisting of core–shell β-NaYF4:Er3+/Yb3+@SiO2 submicron hexagonal prisms

Highly uniform, monodisperse β-NaYF4:Yb3+/Er3+(NYFYE) up-conversion phosphor submicron hexagonal prisms coated with a SiO2 layer are synthesized via a hydrothermal route, forming a core–shell NYFYE@SiO2 crystallites. These crystallites are incorporated into TiO2 nanocrystalline porous film to act as a bifunctional layer and form a composite photoanode employed in dye-sensitized solar cells (DSSCs). The influences of different amount of the NYFYE@SiO2 on the performance of the composite photoanodes and DSSCs are investigated. Studies indicate that by adding NYFYE@SiO2 the light scattering, absorption and near-infrared light harvesting of the composite photoanode are significantly increased, resulting in the great enhancement in the short-circuit current density (Jsc) and photoelectric conversion efficiency (η) of the DSSCs. The optimal properties with an Jsc of 14.91 mA cm−2 and η of 7.28% are obtained in a DSSC with NYFYE@SiO2 content of 15 wt %, increasing significantly by 14% and 29%, respectively, in comparison with those of the DSSC with pure TiO2 photoanode. This significant enhancement in the performance of the DSSCs can be attributed to the enhanced light absorption due to the enhanced light scattering and near-infrared up-conversion of the NYFYE@SiO2 bifunctional layer in the photoanode of the DSSCs.