Papers by Keyword: Upconversion

Abstract: YGdO₃:Er³⁺ nanoparticles were successfully synthesized by pulsed laser ablation in liquid method. The structural and morphological properties of the product are investigated by X-Ray diffraction and transmission electron microscopy. The upconversion photoluminescence properties were investigated in detail. Obvious stark splitting phenomena were observed in the green and red emission bands. The decay behaviors of three emission bands were studied. Based on thermal coupled energy level related upconversion fluorescence intensity ratio, the temperature sensing properties of product were studied. Linear function has beenused to reveal the relationship between fluorescence intensity ratio and temperature. Using stark sublevels related emission bands, sensitivity of the temperature sensor was successfully enhanced. These results suggest the YGdO₃:Er³⁺ nanoparticles prepared via pulsed laser ablation in liquid are promising luminescent materials for optical thermometry.

Abstract: Ho³⁺/Yb³⁺ co-doped ZnO-TiO₂ composite system were synthesized by powder-solution mixing method and their upconversion (UC) luminescence characteristics were investigated under the 980 nm laser excitation. The effect of various ZnO/TiO₂ mixing ratios, and Ho³⁺ and Yb³⁺ concentrations were also studied. The XRD patterns showed that the product fired at 1300 °C consisted of Zn₂TiO₄, TiO₂, RE₂Ti₂O₇, and RE₂TiO₅ (RE = Ho³⁺ and/or Yb³⁺) phases. The green emission centered at 538 nm wavelength was detected as the strongest emission intensity which it was in accordance with the ⁵F_4, ⁵S₂ → ⁵I₈ transition of Ho³⁺ ion. The emission intensity of the product changed by varying ZnO/TiO₂ mixing ratios, and Ho³⁺ and Yb³⁺ concentrations. Brightest UC emission was observed in the sample of 1ZnO:1TiO₂ (in mole) doped with 0.03 mol% Ho³⁺, 9 mol% Yb³⁺ fired at 1300 °C for 1 h. Besides, the dependence of the UC emission intensity on the excitation power indicated that the two-photon process was responsible for this UC system.

Abstract: Pure hexagonal NaYF₄:Yb³⁺,Er³⁺ crystals via doping with Ca²⁺ ions have been successfully prepared by a facile hydrothermal method. The morphology of the crystals was changed from microrods to microprisms. The upconversion (UC) luminescence properties of the as-prepared samples were investigated in detail.

Abstract: Two new anthracene derivatives were synthesized as emitter for low power triplet-triplet annihilation upconversion. Compared with anthracene, the emitter exhibits high quantum yields up to 85%. Pd (II) tetraphenylporphyrin which was selected as the sensitizer with the existence of BBA in DMF, We find a pretty high efficiency (Φuc=21.9%) of the upconversion fluorescence at 532nm with a low excitation power density of 0.5w/cm2.With the comparison of Anthracene, BBA and BTPA systems, quantum yield of the emitter is very important to the improving of the efficiency of upconversion.

Abstract: Hexagonal NaYF⁴:Yb³⁺/Er³⁺ microsheets were successfully synthesized via a hydrothermal method assisted by sodium oxalate as a shape modifier. XRD, FE-SEM, TEM and SAED have been used to study the morphologies and crystal structure of the products. The effects of the pH values on the crystal structure, morphology and size were discussed. The hexagonal NaYF⁴:Yb³⁺/Er³⁺ microsheets show characteristic upconversion fluorescence at green (521-540 nm) and red (630-680 nm) corresponding to the 4f-4f transition of Er³⁺. The green and red emission intensity for microsheets has a great increase compared to that for hexagonal microspheres, and the intensity of the green emission is greater than that of the red one.

Abstract: Rare-earth doped β-NaYbF₄ upconversion phosphors were synthesized using a simple hydrothermal procedure. It is found that under 980 nm excitation β-NaYbF₄:0.1%Tm are more efficient than β-NaYF₄:20%Yb,0.1% that is known as one of the most effective upconversion materials. The unusual result may be related to the particles size. After introducing 0.1%Er³⁺ into the NaYbF₄:0.1%Tm lattice, the upconversion white emission with color coordinate of (0.3016,0.3748) is obtained. The investigation of achieving mechanism indicates that besides the energy transfer from Yb³⁺ to Tm³⁺ and Er³⁺, respectively, there exists a new energy transfer process: ³F_2,3 (Tm³⁺) + ⁴I_11/2 (Er³⁺) → ³F₄ (Tm³⁺) + ²H_11/2/⁴S_3/2 (Er³⁺).

Abstract: Preparation technology and measurement technique have get a great achievement in recent years,that lead to the rapid development of upconversion materials.Some of them achieve a higher fluorescence intensity,or get good hydrophily becase of the application of new type of coupling agent.This would help UCNPs closer to the final goal of business application in Solar Cell, biological fluorescence detection,and optical storage.In this paper,I have introduced the basic conception,luminous mechanism, preparation method of UCNPs,and analyzed the different method could bring what special advantages to them in themself’s specific application field.

Abstract: The major hurdles faced by therapeutic biomolecules to reach clinical use are non-specificity, unnecessary side effects, sensitivity to environmental factors and poor cellular uptake. Several nanoparticle systems have been developed to overcome these issues but there are still some bottlenecks such as nanoparticle toxicity, bioavailability and inability to track the biomolecules post-delivery. Here we report the use of multi-functional lanthanide-based fluorescent upconversion nanoparticles as a safe delivery vector for peptides as well as for fluorescent tracking of delivery or for in-vitro/in-vivo imaging. The UCNs are excited by a NIR light source and emit in the Visible region. Since NIR light is used for excitation, the nanoparticles could be used for deep tissue imaging. Highly monodisperse uniformly sized, sub-100 nm, biocompatible upconversion nanoparticles were synthesized with a mesoporous silica coating. Amanitin, a peptide toxin was used as a model peptide and was loaded onto the mesoporous silica coated UCNs. The peptide loaded UCNs were delivered to B16F0 melanoma cells and significant cell death was achieved within 24 hours. The unloaded UCNs however had negligible toxicity. The UCNs were also used for imaging the cells with very good signal-to-noise ratio and almost nil background autofluorescence. The fluorescence from the UCNs was non-blinking, highly stable and could be used for long-term tracking.

Abstract: Enhancing the up-conversion luminescence and nonlinear optical properties by incorporating various metallic nanoparticles (NPs) into rare earth (RE) doped glass oxides is the key issue towards the fabrication of photonic devices. Series of erbium doped phosphate glasses containing ZnO NPs with composition (78.5-x)P₂O₅ 10Li₂O 10ZnO 1.5Er₂O₃ (x)ZnO, where 0 x 1.2 are prepared by melt quenching technique and their spectroscopic characterization are made. The amorphous nature of the glass is confirmed by XRD spectra. The influence of NPs on the luminescence characteristics using 357 nm excitations is studied and the mechanisms involved in the enhancement on emission intensity are examined. The emission spectra exhibit eight peaks in which the peak intensity of the violet and blue band (413 and 458 nm) shows gradual increment with increasing concentration of ZnO NPs added to the host matrix. The enhancement in the emission peak intensity for the transition is attributed to the effects of quantum confinement and local field of ZnO NPs. The effect of NPs within the glass matrix in influencing the optical properties are analysed and discussed. Our observation may contribute towards the development of nanophotonics.

Abstract: Multicomposition of Er³⁺-Yb³⁺ codoped tellurite oxide, TeO₂-ZnO-PbO-TiO₂-Na₂O glass has been investigated. Detailed spectroscopic study of the Judd-Ofelt analysis has been performed from the measured absorption spectrum in order to obtain the intensity parameters Ω_t (t=2, 4, 6). The calculated Ω_t values were then utilized in the determination of transition probabilities, radiative lifetimes and branching ratios of the Er³⁺ transitions between the J(upper)-J(lower) manifolds. Both visible upconversion and near-infrared spectra were characterized under the 980 nm laser diode excitation at room temperature.