Strong Upconversion Emission Research Articles

Morphology and upconversion properties of rare-earth-doped MoO3 jellyfish-like plate microarchitecture

Here, we report the synthesis of upconversion luminescent MoO3 microplates doped with Er3+-Yb3+ ions through a simple thermal evaporation method. MoO3:Er3+/Yb3+ microplates were composed of a preferred orientation orthorhombic phase with the jellyfish-like morphology of three distinct crystallization zones. A possible growth mechanism such as casted ingot was proposed and the effects of synthesis parameters on microplate morphology were discussed. In addition, the photoluminescence spectrum indicates a strong and pure green upconversion emission under infrared laser excitation. The results demonstrate that evaporation is an effective method to synthesize rare-earth doped MoO3 upconversion materials.

Enhanced Red Upconversion Emission of NaYF4:Yb3+, Er3+, Mn2+ Nanoparticles for Near-infrared-induced Photodynamic Therapy and Fluorescence Imaging

Polyethyleneimine (PEI)-capped NaYF4 nanoparticles (NPs) codoped with Yb3+, Er3+, and Mn2+ ions (MnUNPs) were synthesized via a solvothermal method. The MnUNPs showed tissue-penetrable over-1000 nm (OTN-) near-infrared (NIR) and strong red upconversion (UC) emission under NIR excitation. Furthermore, the photosensitizers chlorin e6 (Ce6) and biocompatible poly(ethylene glycol) (PEG) were immobilized on the surface of the MnUNPs (PEG/Ce6-MnUNPs). The prepared PEG/Ce6-MnUNPs generated singlet oxygen (1O2) and displayed effective anticancer activity under NIR excitation.

Compositional dependence of broadband near-infrared downconversion and upconversion of Yb3+-doped multi-component glasses

Yb3+ single-doped glasses show a strong excitation band in the 300–400 nm region, and efficiently emit photons with wavelengths of 920–1150 nm, and have potential applications in solar cells operating in an extraterrestrial situation. In this work, we systematically study the broadband near-infrared downconversion and upconversion of Yb3+-doped silicate, germanate, phosphate, tellurite and tungsten tellurite glasses. All samples show a broad excitation band in the 300–400 nm range, which is attributed to the charge transfer of the Yb3+–O2− couple. The position of the charge transfer band (CTB) shifts from 300 nm to longer wavelengths around 350 nm when the length of the R–O(Si, P, Ge, Te) increases. The longer R–O gives rise to a smaller central void for Yb3+, thus resulting in a small proportion of Yb3+ ions, thus leading to the blue-shift of the CTB. A smaller proportion of Yb3+ in silicate glasses causes in the strongest upconversion emission at 500 nm.

Two/multi-photon induced up-conversion emission of dicyanoisophorone derivative

Two/multi-photon induced up-conversion emission based on an organic dye is described. Bis(dicyanoisophorone)-1,4-divinylbenzene (1) was synthesized by treatment of 2-(3,5,5-trimethylcyclohex-2-en-1-ylidene)malononitrile and terephthalaldehyde. 1 exhibited strong aggregation-induced emission in solid state, and a large fluorescent quantum yield (ϕf=63%) was obtained. 1 also exhibited nonlinear optical property, a strong up-conversion emission was observed upon excitation with 800–1500nm, and the quadratic dependence of the fluorescence on the excitation laser intensity confirmed the two/multi-photon process.

A Point Temperature Sensor Based on Upconversion Emission in Er3+/Yb3+ Codoped Tellurite-Zinc-Niobium Glass.

Er3+/Yb3+ codoped tellurite-zinc-niobium (TZNb) glass was prepared by the melt-quenching method and used for the construction of a point all-fiber temperature sensor. The glass thermal stability and network structural properties were studied by differential thermal analysis and Raman spectrum, respectively. High glass transition temperature is beneficial to widen the working temperature range. The dependence of fluorescence intensity ratio (FIR) of green upconversion emissions on the surrounding temperature from 276 to 363 K was experimentally investigated and the maximum temperature sensitivity is 95 × 10−4 K−1 at 363 K. Strong green upconversion emission, broad temperature measurement range and high sensitivity indicate this point temperature sensor is a promising optical device for application on optical temperature sensing.

Enhancement of up-conversion emission and emerging cool white light emission in co-doped Yb3+/ Er3+: Li2O-LiF-B2O3-ZnO glasses for photonic applications

Abstract A series of co-doped (Yb 3+ /Er 3+ ): Li 2 O-LiF-B 2 O 3 -ZnO glasses were prepared by standard melt quenching technique. Structural and morphological studies were carried out by XRD and FESEM. Phonon energy dynamics have been clearly elucidated by Laser Raman analysis. The pertinent absorption bands were observed in optical absorption spectra of singly doped and co-doped Yb 3+ /Er 3+ : LBZ glasses. We have been observed a strong up-conversion red emission pertaining to Er 3+ ions at 1.0 mol% under the excitation of 980 nm. However, the up-conversion and down conversion (1.53 µm) emission intensities were remarkably enhanced with the addition of Yb 3+ ions to Er 3+ : LBZ glasses due to energy transfer from Yb 3+ to Er 3+ . Up-conversion emission spectra of co-doped (Yb 3+ /Er 3+ ): LBZ glasses exhibits three strong emissions at 480 nm, 541 nm and 610 nm which are assigned with corresponding electronic transitions of 2 H 9/2 → 4 I 15/2 , 4 S 3/2 → 4 I 15/2 and 4 F 9/2 → 4 I 15/2 respectively. Consequently, the green to red ratio values (G/R) also supports the strong up-conversion emission. The Commission International de E′clairage coordinates and correlated color temperatures (CCT) were calculated from their up-conversion emission spectra of co-doped (Yb 3+ /Er 3+ ): LBZ glasses. The obtained chromaticity coordinates for optimized glass (0.332, 0.337) with CCT value at 5520 K are very close to the standard white colorimetric point in cool white region. These results could be suggested that the obtained co-doped (Yb 3+ /Er 3+ ): LBZ glasses are promising candidates for w-LEDs applications.

Upconversion and downconversion luminescence properties of Er3+ doped NBT ceramics synthesized via hydrothermal method

Er3+-doped Na0.5Bi0.5TiO3 (Er-doped NBT) ceramics were prepared via a hydrothermal method. High sintering active Er-doped NBT nano cubic particles with perovskite structure were synthesized at hydrothermal condition of 200 °C for 24 h in 12 M NaOH solution, which were self-assembled via in situ crystallization mechanism by the initially as-grown nanowires. The Er-doped NBT ceramics sintered at 1100 °C for 2 h exhibit pure rhombohedral perovskite structure, high densification and rather homogenous microstructure morphology. Under 488 nm light excitation, the strong green emission peaks centering at 530 nm and 550 nm and the weak red emission peaks locating at 665 nm and 735 nm are excited, which can be attributed to the 2H11/2, 4S3/2, 4F9/2 and 4I9/2 → 4I15/2 transitions, respectively. The maximum emission intensity is obtained when the Er doping content reaches 1.0 mol%. A strong upconversion emission peak centering around 550 nm in green light range is excited under 800 nm light excitation, which is correlated with the 4S3/2 → 4I15/2 transition.

Up-Conversion in Perovskite Strontium Stannate Nanocrystal Whiskers

We report a simple, eco-friendly facile wet chemical route for the synthesis of pristine and rare–earth metal co-doped (Er/Yb, 10/90, 15/85, 20/80) nano-crystalline, strontium stannate (SrSnO3) whiskers. It is n-type wide bandgap (~4.1 eV) orthorhombic perovskite semiconductor at room temperature, and reveals increase in band gap with the increase in Er/Yb content (from 4.10 to 4.23, 4.30 to 4.39 eV). The samples exhibited strong emission around 365 nm following band-edge excitation by the wavelength of 290 nm. Further, strong up-conversion emission was observed in visible range at the excitation of wavelength 980 nm. The resistivity values were found to decrease with increase in the dopants Er/Yb concentration due to enhancement of charge carriers.

The dominant role of excitation diffusion in energy transfer upconversion of Lu2O3: Tm3+, Yb3+

Emission spectra of Tm3+ and Yb3+ codoped Lu2O3 are studied as a function of the dopant concentration upon 980 nm excitation. The upconverted near infrared emission around 811 nm from Tm3+:3H4→3H6 transition is observed due to two step energy transfers from Yb3+ through Tm3+:3F4 as the intermediate level. The optimal dopants concentrations for the strongest upconversion emission are 0.1 mol% Tm3+ and 4 mol% Yb3+. The dependence of energy transfer coefficients for the two step energy transfers on Tm3+ and/or Yb3+ concentration is studied. The obtained results indicate that the excitation diffusions among Yb3+ ions and among Tm3+ ions mainly control the energy transfer rates for the optimal dopants concentrations and thus dominate the energy transfer upconversion process.

Highly uniform up-converting nanoparticles: Why you should control your synthesis even more

Luminescent β-NaYF4:Yb3+,Er3+ (xYb: 0.17, xEr: 0.03) nanomaterials were synthesized for use as labels for biomedical applications with high temperature co-precipitation synthesis in 1-octadecene and oleic acid. The effect of the synthesis conditions (e.g. argon flow, cooling and stirring rates) on the products’ up-conversion luminescence intensity, particle size and morphology were studied. The factors contributing to these properties were analysed. It was observed that an efficient inert gas flow is essential to the formation of the preferred highly-luminescent hexagonal structure. Furthermore, the flow rate, together with the stirring rate, crucially affect the Er:Yb molar ratio of the products. The optimization of this ratio is essential when strong up-conversion emission is required from small particles, whereas the morphology and uniformity of the nanoparticles can be controlled with the cooling rate. These results emphasize the importance of controlling the synthesis conditions, especially when nanoparticles need to have a specific morphology because of their use e.g. as luminescent labels in medical diagnostics.

Microwave-hydrothermal synthesis, characterization and upconversion luminescence of rice-like Gd(OH)3 nanorods

Rice-like Gd(OH)3 nanorods were successfully prepared through a facile and rapid microwave-hydrothermal synthesis method without using any surfactants or templates. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy-dispersive spectroscopy (EDS) were used to characterize the samples. Results show that the nanorods have an average length of 400 nm and an average diameter of 50 nm. The effects of reaction parameters such as reaction temperature and time on the preparation were briefly investigated. It is found that the crucial factor for the formation of rice-like Gd(OH)3 nanorods is reaction time. When the rice-like Gd(OH)3 nanorods was codoped with Yb3+ and Er3+, strong upconversion emissions could be observed under the excitation of 980-nm-laser, and the calculated CIE color coordinates falls within the yellow region, which may be potential candidate for optical materials.

Upconversion luminescence properties of Y2O2S:Er3+@Y2O2S:Yb3+,Tm3+ core-shell nanoparticles prepared via homogeneous co-precipitation

The Y2O2S:Er3+@Y2O2S:Yb3+,Tm3+ core-shell upconversion (UC) nanoparticles with average diameter of 95 nm were synthesized by the homogeneous co-precipitation method combining with the solid-gas sulfidation route. The increases of nanocrystaline size after the shell coating was observed both in the X-ray diffraction (XRD) and transmission electron microscope (TEM) measurements. This indicates the composition homogeneity core-shell Y2O2S nanocrystals. Meanwhile, the luminescence of both the Er3+ and Tm3+ ions are realized for the first time in the novel core-shell Y2O2S:Er3+@Y2O2S:Yb3+,Tm3+ nanoparticles under the excitations of both 980 and 1550 nm. When excited by a 980 nm laser diode, the Y2O2S:Er3+@Y2O2S:Yb3+,Tm3+ phosphor exhibits blue (≈475 nm), green (≈548 nm) and red (≈670 nm) emissions in the visible region, which correspond to the 1G4 → 3H6 transition of Tm3+ions, 4S3/2, 2H11/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ ions, respectively. The very strong emission at the near infrared (NIR) region is mainly due to the 3H4 → 3H6 transition of Tm3+ ions. The emission from both of Er3+ and Tm3+ ions under 980 nm excitation reveals the energy transfers of Yb3+ → Tm3+ within the shell layer and Yb3+ → Er3+ between the shell and the core. When pumping at 1550 nm, although only Er3+ ions can efficiently absorb the excitation energy, the strong UC emissions from Tm3+ ions were also observed. This is owing to the energy transfer between the core and the shell through Er3+ → Yb3+ → Tm3+ ions.

CdS bulk crystal growth by optical floating zone method: strong photoluminescence upconversion and minimum trapped state emission

CdS materials have shown promise in optical refrigeration. However, the current success of laser cooling is still limited to nanobelt morphology. It is, therefore, important to explore whether bulk crystal growth technology could provide high-quality materials for laser cooling studies. Herein, we have demonstrated CdS bulk crystal growth by a modified optical floating zone method. The low temperature and continuous displacement of the CdS crystalline zone have resulted in high-quality CdS bulk crystals, which show strong photoluminescence upconversion with the absence of the long-wavelength and broad emission centered ∼700 nm that commercial CdS wafers usually exhibit. All these characterizations have confirmed the excellent stoichiometric nature and crystal quality of CdS bulk crystals, which is much better than the commercial counterparts for laser cooling studies.

Optimization of Bi3+ in Upconversion Nanoparticles Induced Simultaneous Enhancement of Near-Infrared Optical and X-ray Computed Tomography Imaging Capability.

Bioimaging probes have been extensive studied for many years, while it is still a challenge to further improve the image quality for precise diagnosis in clinical medicine. Here, monodisperse NaGdF4:Yb3+,Tm3+,x% Bi3+ (abbreviated as GYT-x% Bi3+, x = 0, 5, 10, 15, 20, 25, 30) upconversion nanoparticles (UCNPs) have been prepared through the solvothermal method. The near-infrared upconversion emission intensity of GYT-25% Bi3+ has been enhanced remarkably than that of NaGdF4:Yb3+,Tm3+ (GYT) with a factor of ∼60. Especially, the near-infrared upconversion emission band centered at 802 nm is 150 times stronger than the blue emission band of GYT-25% Bi3+ UCNPs. Such high ratio of NIR/blue UCL intensity could reduce the damage to tissues in the bioimaging process. The possibility of using GYT-25% Bi3+ UCNPs with strong near-infrared upconversion emission for optical imaging in vitro and in vivo was performed. Encouragingly, the UCL imaging penetration depth can be achieved as deep as 20 mm. Importantly, GYT-25% Bi3+ UCNPs exhibit a much higher X-ray computed tomography (CT) contrast efficiency than GYT and iodine-based contrast agent under the same clinical conditions, due to the high X-ray attenuation coefficient of bismuth. Hence, simultaneous remarkable enhancement of NIR emission and X-ray CT signal in upconversion nanoparticles could be achieved by optimizing the doping concentration of Bi3+ ions. Additionally, Gd3+ ions in the UCNPs endow GYT-25% Bi3+ UCNPs with T1-weighted magnetic resonance (MR) imaging capability.

Near-infrared (808 and 980 nm) excited photoluminescence study in Nd-doped Y2O3 phosphor for bio-imaging

The upconversion (UC) process in lanthanide-doped nanophosphors has attracted great research interest for its extensive application potential in biological in vitro and in vivo imaging due to the high tissue penetration depth of near-infrared excitation and low autofluorescence background. In this article, the authors report the synthesis of oxide nanophosphor of size ⩽50 nm, which forms stable aqueous dispersion. The photoluminescence study is made on the nanophosphor upon 808 and 980 nm diode laser excitations. The 808 nm excitation resulted in strong emission at 795 nm due to the 4K13/2 → 4I13/2 transition along with other emissions from the Nd3+ ion. The 980 nm excitation has resulted in it turning green in the 525–560 nm range and is assigned to the 4S3/2 → 4I15/2 transition of the Er3+ ion, which is supposed to be present in a trace amount in the sample. The observation of strong UC emission indicates that the sample can be used for UC-based bio-imaging applications.

Versatile, Fast, and Easy One‐Step Method for the Synthesis of Hydrophilic Lanthanide‐Doped Nanoparticles

AbstractThe preparation of hydrophilic lanthanide‐doped nanoparticles (NPs) following a versatile one‐step colloidal method at low temperature and short reaction time with different doped lanthanides, capping ligands, and fluoride sources is presented. The photoluminescence of the particles, via both downshifting (DS) and up‐conversion (UC), was easily tuned from blue or green by simply changing the lanthanides used. When using the same core type of particles, the size and the photoluminescence intensity were tuned by changing the fluoride source or the capping ligand used: the size of the DSNPs varied from 9 nm (PAA) to 24 nm (PEI) when changing the capping ligand, while if PAA was used as capping ligand, the nanoparticles presented the most intense emission bands. Supramolecular host groups were introduced on the surface of the UCNPs by grafting cyclodextrin (CD) groups onto the capping ligand PiBMA prior to particle synthesis, reaching a CD surface density of 0.28 CD nm‐2. In this case, a small particle size (11.7 nm) and strong UC emission bands were observed.

Fabrication of novel Ba4Y3F17:Er3+ nanofibers with upconversion fluorescence via combination of electrospinning with fluorination

PVP/[Ba(CH3COO)2 + Y(NO3)3 + Er(NO3)3] composite nanofibers were prepared via electrospinning, and then mixed oxide nanofibers were obtained by calcining the composite nanofibers in air, and finally Ba4Y3F17:Er3+ nanofibers were successfully synthesized by fluorination of the as-prepared mixed oxide nanofibers used as precursor via a double-crucible method applying NH4HF2 as fluorinating agent. X-ray diffraction (XRD) analysis reveals that Ba4Y3F17:Er3+ nanofibers are pure rhombohedral phase. The diameter of Ba4Y3F17:Er3+ nanofibers is 84.3 ± 4.9 nm under the 95 % confidence level. Upconversion emission spectra analysis manifests that Ba4Y3F17:Er3+ nanofibers emit strong green and weak red upconversion emissions centering at 523 (2H11/2 → 4I15/2), 541 (4S3/2 → 4I15/2) and 652 (4F9/2 → 4I15/2) nm, respectively, and the emitting colors of Ba4Y3F17:Er3+ nanofibers are located in the green region in CIE chromaticity coordinates diagram. The optimum doping molar concentration of Er3+ ions is found to be 9 %. Moreover, the formation mechanism and upconversion luminescence of the Ba4Y3F17:Er3+ nanofibers are also investigated. This novel preparation technique can be applied to prepare other rare earth fluoride one-dimensional nanomaterials.

Facile synthesis of Gd_2O_3:Ho^3+/Yb^3+ nanoparticles: an efficient upconverting material for enhanced photovoltaic performance of dye-sensitized solar cells

A series of Ho3+/Yb3+-codoped Gd2O3 nanoparticles were prepared by a facile urea-based homogeneous precipitation method. Under the excitation of 980 nm light, all the samples exhibited strong green and red upconversion (UC) emissions corresponding to the (5F4,5S2) → 5I8 and 5F5 → 5I8 transitions of Ho3+ ions, respectively. A gradual enhancement in the UC emission intensity was observed with increasing the Yb3+ ion concentration, achieving its optimum value when the doping concentration was 3 mol%. In addition, with the introduction of Ho3+/Yb3+-codoped Gd2O3 nanoparticles into the TiO2 porous film of dye-sensitized solar cells (DSSCs), the power conversion efficiency of the cells (7.403%) was ~10.47% higher than that of the DSSCs with pure TiO2 porous film (6.701%), which is mainly caused by increased short-circuit current density due to their enhanced light-harvesting properties via an efficient UC process. The result suggested that the incorporation of upconverting nanoparticles into the TiO2 porous film is an effective approach to improve the photovoltaic characteristics of DSSCs.

A new scheme to acquire BaY2F8:Er3+ nanofibers with upconversion luminescence

PVP/[Ba(CH3COO)2 + Y(NO3)3 + Er(NO3)3] composite nanofibers were prepared via electrospinning, and then the mixed oxide nanofibers were obtained by calcination of the above composite nanofibers. BaY2F8:Er3+ nanofibers were successfully fabricated via a double-crucible fluorination method by using the prepared mixed oxide nanofibers as precursor. X-ray diffraction analysis reveals that BaY2F8:Er3+ nanofibers are pure monoclinic phase with space group of C2/m. The diameter of BaY2F8:Er3+ nanofibers is 159.9 ± 15.9 nm under the 95 % confidence level. Upconversion fluorescent spectroscopy analysis manifests that BaY2F8:Er3+ nanofibers emit strong green and weak red upconversion emissions centering at 523 (2H11/2 → 4I15/2), 540 (4S3/2 → 4I15/2) and 652 (4F9/2 → 4I15/2) nm, respectively, and the emitting colors of BaY2F8:Er3+ nanofibers are located in the green region in CIE chromaticity coordinates diagram. The optimum doping molar concentration of Er3+ ions in the BaY2F8:Er3+ nanofibers is found to be 5 %. The formation process and upconversion luminescence mechanism of the BaY2F8:Er3+ nanofibers are also studied. This novel preparative technique can be applied to fabricate other rare earth fluoride one-dimensional nanomaterials.

Multifunctional Coordination Polymer Nanoparticles Based on Allantoin: Single Peak Upconversion Emission, Drug Delivery and Cytotoxicity Study

In this work, multifunctional coordination polymer (CP) nanoparticles with strong single peak upconversion emission and high drug loading capacity were prepared via a facile solvothermal method. Various experimental parameters, such as reaction time, reaction temperature and reagent concentration were studied in detail. A series of measurements were carried out to characterize the product. Results show the CP particles with a mean diameter of approximately 80 nm can be prepared by finely selecting the preparation conditions. Strong single peak upconversion emission centering at 675 nm is observed on excitation with 980 nm laser. Drug loading and releasing experiments reveal that the CP nanospheres have a loading capacity of 200 mg/g and 50.3 % of the loaded fluorescein isothiocyanate can be released in 18 h. Cytotoxicity study displays that the CP nanospheres are biocompatible.