Synthesis of NaYF4:Ho3+/Yb3+ colloidal upconversion phosphor and its application for OCT-based imaging, temperature sensing, fingerprinting and security ink

In this work, an NaYF4:Ho3+/Yb3+ upconversion phosphor in colloidal form was synthesized and then its suitability for image contrast enhancement in optical coherence tomography (OCT) and photothermal (PT) OCT imaging was analysed.

Strategic combination of ultra violet-visible-near infrared light active materials towards maximum utilization of full solar spectrum for photocatalytic chromium reduction

Maximum utilization of the full solar spectrum has been considered as a holy grail in the field of photocatalysis and has emerged important in the recent years, as the world needs to move towards renewable energy sources and also to maintain environmental health. In the search for a sustainable solution, we have come up with a strategic combination of materials, which can be active under all the three regions, namely ultraviolet (UV), visible and near infrared (NIR) of the sunlight. Specifically, we have developed a series of nanocomposites comprising of two dimensional nanosheets of zinc oxide (ZnO) and graphitic carbon nitride (GCN), and successfully coupled them with upconversion nanoparticles (UCNP). These nanocomposites have been successfully utilized for the photocatalytic chromium (Cr(VI)) reduction. The prepared nanocomposites exhibit an excellent photocatalytic activity toward reduction of Cr(VI) under different light region. A plausible mechanism for the photocatalytic process has been proposed based on the detailed study. This work is expected to pave way for the strategic design and development of many photocatalytic systems, which can utilize sunlight to the maximum extent.

Spatially confined luminescence process in tip-modified heterogeneous-structured microrods for high-level anti-counterfeiting

Recent years have witnessed the progress of lanthanide-doped materials from fundamental material synthesis to targeted practical applications such as optical applications in photodetection, anti-counterfeiting, volumetric display, optical communication, as well as biological imaging. The unique compositions and structures of well-designed lanthanide ion-doped materials could expand and strengthen their application performances. Herein, we report dual-mode luminescent crystalline microrods that spatially confine upconversion and downconversion photophysical process within defined regions using the specially designed heterogeneous structure. Through an epitaxial growth procedure, downconversion tips have been conjugated with the parent upconversion microrods in oriented directions. This spatially confined structure can effectively depress the deleterious energy depletion in lanthanide ions homogeneously doped materials, and as a result, the red, green, and blue upconversion intensities have been enhanced by 334, 225, and 22 times, respectively. Moreover, the induced tips hardly disturb the upconversion process of the microrod seeds. Upon 980 nm laser or ultraviolet lamp excitation, tunable emission colors were realized in the single tip-modified microrod, indicating potential applications of these microrods for high-level dual-mode anti-counterfeiting.

Facile synthesis and color-tunable properties of monodisperse β-NaYF4:Ln3+ (Ln = Eu, Tb, Tm, Sm, Ho) microtubes

In this study, monodisperse and uniform β-NaYF₄ hexagonal microtubes were successfully synthesized via a simple hydrothermal method without any organic surfactants, employing Y(OH)CO₃ colloid spheres as precursors.

An assembly and interaction of upconversion and plasmonic nanoparticles on organometallic nanofibers: enhanced multicolor upconversion, downshifting emission and the plasmonic effect

We present novel inorganic-organic hybrid nanoparticles (HNPs) constituting inorganic NPs, NaY_0.78Er_0.02Yb_0.2F₄, and organometallic nanofiber, Tb(ASA)₃Phen (TAP). X-ray diffraction, Fourier transform infrared absorption and transmission electron microscopy analyses reveal that prepared ultrafine upconversion NPs (UCNPs (5-8 nm)) are dispersed on the surface of the TAP nanofibers. We observe that the addition of TAP in UCNPs effectively limits the surface quenching to boost the upconversion (UC) intensity and enables tuning of UC emission from the green to the red region by controlling the phonon frequency around the Er³⁺ ion. On the other hand, TAP is an excellent source of green emission under ultraviolet exposure. Therefore prepared HNPs not only give enhanced and tunable UC but also emit a strong green color in the downshifting (DS) process. To further enhance the dual-mode emission of HNPs, silver NPs (AgNPs) are introduced. The emission intensity of UC as well as DS emission is found to be strongly modulated in the presence of AgNPs. It is found that AgNPs enhance red UC emission. The possible mechanism involved in enhanced emission intensity and color output is investigated in detail. The important optical properties of these nano-hybrid materials provide a great opportunity in the fields of biological imaging, drug delivery and energy devices.

Highly efficient NIR to NIR upconversion of ZnMoO4:Tm3+,Yb3+ phosphors and their application in biological imaging of deep tumors

In vivo imaging of deep tumor in nude-mice was successfully demonstrated using highly efficient ZnMoO₄:Tm³⁺,Yb³⁺,K⁺ nano-phosphors and an 810 nm NIR laser.

Enhanced white light emission from a Tm3+/Yb3+/Ho3+ co-doped Na4ZnW3O12 nano-crystalline phosphor via Li+ doping

This paper reports white light emission from a Tm³⁺/Yb³⁺/Ho³⁺ co-doped Na₄ZnW₃O₁₂ nano-crystalline phosphor synthesized through a solution combustion method.

Mechanisms of the blue emission of NaYF4:Tm3+ nanoparticles excited by an 800 nm continuous wave laser

Simultaneous multiwavelength excitation and the quantum transition principle are utilized to study the blue emission mechanisms of NaYF₄:Tm³⁺ UCNPs under 800 nm CW laser excitation.

Enhancement of near-infrared to near-infrared upconversion luminescence in sub-10-nm ultra-small LaF(3):Yb(3+)/Tm(3+) nanoparticles through lanthanide doping

In this Letter, I present a versatile strategy to enhance the near-infrared to near-infrared (NIR-to-NIR) upconversion luminescence from sub-10-nm ultra-small LaF(3):Yb(3+)/Tm(3+) colloidal nanoparticles through lanthanide doping under 980 nm laser excitation. It is interesting that the NIR-to-NIR upconversion emission at 801 nm of LaF(3):Yb(3+)Tm(3+) nanoparticles can be improved by increasing the Tm(3+) doping concentration or by introducing another lanthanide activator (Er(3+) or Ho(3+)) as a sensitizer. The luminescence enhancement effect showed a strong dependence on the doping concentrations of activator ions (Tm(3+), Er(3+), or Ho(3+)). Particularly, adding 1 mol. % Ho(3+) ions into LaF(3):Yb(3+)Tm(3+) nanoparticles induced a 2.85-fold enhancement in NIR 801 nm emission of Tm(3+) ions. The related upconversion emission mechanisms were investigated and discussed.

Up/down conversion switching by adjusting the pulse width of red laser beams in LaF₃:Tm³⁺ nanocrystals

We demonstrate a versatile approach to fine-tuning the ratio of blue to near-infrared emission intensity from Tm3+ ions in LaF3 nanocrystals by adjusting the pulse widths and excitation wavelengths of red laser beams. The mechanism of color-tunable Tm3+ emission by pulse widths is explored, and a mechanism based on promoting the population of some luminescence levels and cutting off the population of others by suitably adjusting pulse duration is proposed. The underlying reason of excitation wavelength-modulated emission is ascribed to tuning absorption probability ratio of ground state absorption to excited state absorption by tuning the matching degree between the energies of excitation wavelength and ground (excited) state absorption of Tm3+. The ability of our LaF3:Tm3+ nanocrystals to emit variable emissions on demand in response to pulse width and excitation wavelength provides keen insights into controlling the population processes of luminescent levels and offers a versatile approach for tuning the spectral output.

Phonon-assisted energy back transfer-induced multicolor upconversion emission of Gd2O3:Yb3+/Er3+ nanoparticles under near-infrared excitation

By harnessing the phonon-assisted energy back transfer (EBT) from Er³⁺ to nearby Yb³⁺ ions, we obtain continuous multicolor (from green to red) UC fluorescence in the Gd₂O₃:Yb³⁺/Er³⁺ UCNPs.

Highly efficient NIR–NIR upconversion in potassium substituted CaMoO4:Tm3+, Yb3+ phosphor for potential biomedical applications

Highly efficient NIR to NIR upconversion in CaMoO₄:Tm³⁺, Yb³⁺ nanocrystals pumped by less than 1 mW laser was achieved for biomedical applications.

Crystal structure and photoluminescence of two europium compounds with phenoxyacetic acid and 2,4,6-tri(2-pyridyl)-s-triazine

Two europium crystals with HPOA and TPTZ were prepared and the heteronuclear compound exhibits superior luminescence properties compared to the homonuclear one.

Unusual upconversion emission from single NaYF4:Yb3+/Ho3+ microrods under NIR excitation

Rare earth ion-doped upconversion materials show great potential applications in optical and optoelectronic devices due to their novel optical properties.

Formation of bundle-shaped β-NaYF4 upconversion microtubes via Ostwald ripening

In this work, the uniform bundle-shaped microtubes composed of six half-pipes are synthesized for the first time in hydrothermal solutions via an intentional delayed phase transition pathway induced by Mn(2+) doping. The structural and kinetic factors that govern the phase and shape evolution of NaYF4 microcrystals have been carefully studied, and the influences of Mn(2+) to RE(3+) ratio, the amount of trisodium citrate, and the pH value in conjunction with the intrinsic character of RE(3+) ions on the phase and shape evolution are systematically discussed. It is found that the proper Mn(2+) to RE(3+) ratio is mainly responsible for delayed phase transition process and induces interior density gradient of solid aggregate for creating hollow bundle-shaped microtubes. While the amount of trisodium citrate and the pH value are the keys for the shape control of the NaYF4 microcrystals such as prismatic microtubes, prismatic short rods, thin plates, and particles. The up and downconversion emissions were obtained independent of whether α- or β-NaYF4:Er(3+)/Yb(3+) samples doped with Mn(2+), but the significant tuning of output color was only obtained in cube NaYF4 nanoparticles rather than in hexagonal microtubes via adjusting the amount of Mn(2+) ions. These spectral measurements and EDX analyses indicate that the distribution or concentration of Mn(2+) in hexagonal phase solid solution has changed, which supports Ostwald ripening growth mechanism and rules out agglomeration or oriented attachment growth mechanism. We designed crystal growth mode by simply addition of dopant may provide a versatile approach for fabricating a wide range of hollow nano/microcrystals and thus bring us a clearer understanding on the interaction between the dopant reagents and the nano/microcrystals.