Core/shell structured NaYF4:Yb3+/Er3+/Gd+3 nanorods with Au nanoparticles or shells for flexible amorphous silicon solar cells

A simple approach for preparing near-infrared (NIR) to visible upconversion (UC) NaYF4:Yb/Er/Gd nanorods in combination with gold nanostructures has been reported. The grown UC nanomaterials with Au nanostructures have been applied to flexible amorphous silicon solar cells on the steel substrates to investigate their responses to sub-bandgap infrared irradiation. Photocurrent–voltage measurements were performed on the solar cells. It was demonstrated that UC of NIR light led to a 16-fold to 72-fold improvement of the short-circuit current under 980 nm illumination compared to a cell without upconverters. A maximum current of 1.16 mA was obtained for the cell using UC nanorods coated with Au nanoparticles under 980 nm laser illumination. This result corresponds to an external quantum efficiency of 0.14% of the solar cell. Mechanisms of erbium luminescence in the grown UC nanorods were analyzed and discussed.     

Synthesis of colloidal upconverting NaYF4: Er3+/Yb3+ and Tm3+/Yb3+ monodisperse nanocrystals

The synthesis, characterization, and spectroscopy of upconverting lanthanide-doped NaYF4 nanocrystals (NCs) is presented. The monodisperse cubic NaYF4 NCs were synthesized via a thermal decomposition reaction of trifluoroacetate precusors in a mixture of technical grade chemicals, octadecene and the coordinating ligand oleic acid. In this straightforward method, the dissolved precursors are added slowly to the reaction solution through a stainless-steel canula resulting in highly luminescent nanocrystals with an almost monodisperse particle size distribution. The NCs were characterized through the use of transmission electron microscopy, selected area electron diffraction, 1H NMR, powder X-ray diffraction, and high-resolution luminescence spectroscopy. The NaYF4 NCs are capable of being of dispersed in nonpolar organic solvents thus forming colloidally stable solutions. The colloids of the Er3+, Yb3+ and Tm3+, Yb3+ doped NCs exhibit green/red and blue upconversion luminescence, respectively, under 980 nm laser diode excitation with low power densities.     

Multicolor upconversion of Er3+/Tm3+/Yb3+ doped oxyfluoride glass ceramics

Er³⁺/Tm³⁺/Yb³⁺ tridoped oxyfluoride glass ceramics was synthesized in a general way. Under 980 nm LD pumping, intense red, green and blue upconversion was obtained. And with those primary colors, multicolor luminescence was observed in oxyfluoride glass ceramics with various dopant concentrations. The red and green upconversion is consistent with ⁴F_9/2 → ⁴I_15/2 and ²H_11/2, ⁴S_3/2 → ⁴I_15/2 transition of Er³⁺ respectively. While the blue upconversion originates from ¹G₄ → ³H₆ transition of Tm³⁺. This is similar to that in Er³⁺/Yb³⁺ and/or Tm³⁺/Yb³⁺ codoped glass ceramics. However the upconversion of Tm³⁺ is enhanced by the energy transfer between Er³⁺ and Tm³⁺.     

Ion-exchanged waveguide lasers in Er3+/Yb3+ codoped silicate glass

We investigated an Er(3+)/Yb(3+) codoped silicate glass as a host material for waveguide lasers operating near 1.5 mum. Spectroscopic properties of the glass are reported. Waveguide lasers were fabricated by K(+)-ion exchange from a nitrate melt. The waveguides support a single transverse mode at 1.5 mum. An investigation of the laser performance as a function of the Yb:Er ratio was performed, indicating an optimal ratio of approximately 5:1. Slope efficiencies of as great as 6.5% and output powers as high as 19.6 mW at 1.54 mum were realized. The experimental results are compared with a waveguide laser model that is used to extract the Er(3+) upconversion coefficients and the Yb(3+)-Er(3+) cross-relaxation coefficients. The results indicate the possibility of obtaining high-performance waveguide lasers from a durable silicate host glass.     

NaYF4:Er3+和NaYF4:Yb3+/Er3+上转换荧光纳米晶的制备与表征

以EDTA为螯合剂,采用络合共沉淀法合成了NaYF4:Er3+和NaYF4:Yb3+/Er3+纳米晶.分别采用XRD、SEM、荧光分光光度计对合成的样品进行了结构、形貌和上转换荧光分析.XRD结果表明,制备的NaYF4:Er3+和NaYF4:Yb3+/Er3+均为纯立方相;SEM结果显示,制备的NaYF4:Er3+和NaYF4: Yb3+/Er3+晶粒粒径都在100nm左右,与NaYF4:Er3+相比,NaYF4:Yb3+/Er3+晶粒尺寸分布更均匀,分散性更好,符合作为荧光标记材料的要求;上转换荧光分析表明,在980nm激光器激发下,NaYF4:Yb3+/Er3+的发光强度比NaYF4:Er3+提高了1个数量级.     

纳米NaYF4:Er3+,Yb3+上转换材料的合成及其性质研究

采用溶胶-凝胶法在水相合成了纳米NaYF_4:Er~(3 ),Yb~(3 )上转换材料,980nm红外激光照射下,肉眼可观察到明亮的上转换发光。实验研究了铒、镱掺杂浓度及焙烧温度对材料合成的影响。所合成的纳米材料呈圆球形、颗粒均匀、分散性好,平均粒径70nm,可应用于生物标记。     

Broadband emission from Ce3+/Mn2+/Yb3+ tri-doped oxyfluoride glasses for glass greenhouse

In this work, a kind of oxyfluoride glasses tri-doped with Ce³⁺/Mn²⁺/Yb³⁺ ions was prepared by a simple and fast high temperature melting method. Under excitation with 300 nm light, two meaningful broad band emissions (ranged from 340 to 500 nm and 510–700 nm) were obtained, which matched well with the absorption of the chlorophylls. Under near-infrared (980 nm) excitation, an abnormal up-conversion luminescence was demonstrated in the oxyfluoride glasses by the energy transfer from Yb³⁺ to Mn²⁺. In addition, the up-conversion emission has a red shift along with the increase of the doping concentration of Mn²⁺, which would contribute to match the action spectrum of photosynthesis better. Our materials will be favored to extend the utilization of solar energy in glass greenhouse for plant cultivation.     

Up-conversion luminescence and optical temperature sensing behaviour of Yb3+/Er3+ codoped CaWO4 material

Present article report on structural and optical properties of Er³⁺/Yb³⁺ codoped CaWO₄ phosphors. Structural properties are explored using XRD and Raman technologies. The upconversion emission has been investigated with 980 nm excitation. The upconversion emission intensity is dependent on the concentrations of Yb³⁺ ions and reaches a maximum at 7%. Logarithmic plots of power dependencies reveal that the green and red emissions originate from a two-photon upconversion process. Based on the photon energy and the emission spectra, the possible upconversion processes and emission mechanisms are discussed. Finally, the optical temperature sensing properties has been performed using the fluorescence intensity ratio technique based on green upconversion emissions. Its temperature sensitivity is found to be above 0.0025 K^-1 in the whole temperature range of 300–540 K, revealing this phosphor to be a promising optical temperature sensing material.     

微波水热合成六方相NaYF4以及Yb3＋、Er3＋掺杂NaYF4微米管

为了合成单相以及Yb3+、 Er3+掺杂的六方结构NaYF4,采用微波水热的方法,以稀土硝酸盐、氟化钠、柠檬酸、氢氧化钠、乙酸乙酯和水为原料,合成了六方相NaYF4以及Yb3+、Er3+掺杂的六方相NaYF4 (NaYF4 ∶ Yb3+,Er3+)微米管. 利用XRD、SEM对所得样品的物相和形貌进行了表征. 研究了不同反应条件对产物形貌和物相的影响,并提出了NaYF4微米管的形成机理. 研究发现,采用微波加热的方法可以在较低的温度下快速得到单一六方相的NaYF4. 所制备的Yb3+、 Er3+掺杂NaYF4微米管的上转换发光性能与其体材料类似,具有较高的发光强度.     

Influences of Er3+ content on structure and upconversion emission of oxyfluoride glass ceramics containing CaF2 nanocrystals

Transparent 45SiO₂–25Al₂O₃–5CaO–10NaF–15CaF₂ glass ceramics doped with different content of erbium ion (Er³⁺) were prepared. X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses evidenced the spherical CaF₂ nanocrystals homogeneously embedded among the glassy matrix. With increasing of Er³⁺ content, the size of CaF₂ nanocrystals decreased while the number density increased. The crystallization kinetics studies revealed that CaF₂ crystallization was a diffusion-controlled growth process from small dimensions with decreasing nucleation rate. Er³⁺ could act as nucleating agent to lower down crystallization temperature, while some of them may stay at the crystal surfaces to retard the growth of crystal. Intense red and weak green upconversion emissions were recorded for glass ceramics and their intensities increased with the increasing of Er³⁺ content under 980 nm excitation. However, the concentration quenching effect appeared when Er³⁺ doping reached 2 mol%. These results could be attributed to the change of ligand field of Er³⁺ ions due to the incorporation of Er³⁺ ions into precipitated fluoride nanocrystals.     

Near-infrared quantum cutting in Bi3+/Yb3+ co-doped oxyfluoride glasses via cooperative energy transfer for solar cells

The Bi³⁺/Yb³⁺ ion co-doped 55SiO₂–20Al₂O₃–5Na₂CO₃–20CaF₂ glasses are synthesized successfully by a conventional melting-quenching method. High efficient quantum cutting involving the emission of two near-infrared photons for one ultraviolet photon absorbed is realized in the oxyfluoride glasses co-doped with Bi³⁺ and Yb³⁺. An intense characteristic near-infrared emission around 977 nm of Yb³⁺:²F_5/2 → ²F_7/2 transition is obtained when the 303 nm is as excitation wavelength to induce the ¹S₀ → ³P₁ transition of Bi³⁺. The maximum quantum efficiency of our glasses is estimated to be 164.3%. The energy transfer mechanism is proposed to be a cooperative energy transfer via second-order down-conversion process. The glasses could be a potential quantum cutting converter to improve the photovoltaic energy conversion efficiency of crystalline Si solar cells via spectrum modification.     

Synthesis and characterization of upconverting NaYF4:Er3+, Yb3+ nanocrystals via thermal decomposition of stearate precursor

Er3+-Yb3+ codoped hexagonal NaYF4 nanocrystals were prepared via a method of thermal decomposition of stearate precursor. Their crystal structure, morphologies and photoluminescence (PL) properties were characterized by XRD, SEM, and fluorescence spectra. The hexagonal NaYF4:Er3+, Yb3+ nanocrystals could be well dispersed in cyclohexane to form a clear solution. Under 980 nm excitation, the solution of Er3+-Yb3+ codoped NaYF4 nanocrystals emits bright green upconversion fluorescence.     

Upconversion emission from Yb3+ and Tm3+ codoped NaYF4 thin film prepared by thermal evaporation

Yb3+ and Tm3+ codoped fluoride thin film, with intense ultraviolet and visible upconversion emissions under 980 nm excitation, has been deposited on an Al2O3 ceramic substrate by thermal evaporation under high vacuum. NaY(0.835)Yb(0.15)Tm(0.015)F4 bulk material synthesized by high temperature solid-state reaction was used as target in preparing the thin film. Yb3+ and Tm3+ codoped system, which had been reported before, had been studied. Compared with the unannealed thin film, the annealed film showed better upconversion emission properties, especially in the ultraviolet region, given in the normalized upconversion emission spectra, due to the structure changed from amorphous to hexagonal NaYF4 (beta-NaYF4) during the annealing process. The upconversion mechanism of the thin film was also discussed in this paper.     

Partition, luminescence and energy transfer of Er/Yb ions in oxyfluoride glass ceramic containing CaF2 nano-crystals

A complete spectroscopic investigation of energy transfer processes in oxyfluoride glass ceramics containing CaF₂ nano-crystals doped with various amounts of Er³⁺ and Yb³⁺ was reported. An enhancement of the 1.53 μm emission and infrared to visible up-conversion fluorescence was confirmed experimentally due to efficient non-radiative energy transfer from Yb³⁺ to Er³⁺ ions concentrated in CaF₂ nano-crystals. The efficiency of Yb³⁺ to Er³⁺ energy transfer in excess of 85% was obtained for 0.5 mol% Er³⁺/2.0 mol% Yb³⁺ co-doped glass ceramic. Using rate equation formulism, the coefficient of Yb³⁺ to Er³⁺ energy transfer was determined to be about 3.5 times higher than that of Er³⁺ to Yb³⁺ energy back transfer, which is sufficient to provide high ⁴I_11/2 population of Er³⁺ to improve the fluorescence of the co-doped glass ceramics.     

Silver doping of silica-hafnia waveguides containing Tb3+/Yb3+ rare earths for downconversion in PV solar cells

The aim of this paper is to study the possibility to obtain an efficient downconverting waveguide which combines the quantum cutting properties of Tb³⁺/Yb³⁺ codoped materials with the optical sensitizing effects provided by silver doping. The preparation of 70SiO₂–30HfO₂ glass and glass-ceramic waveguides by sol-gel route, followed by Ag doping by immersion in molten salt bath is reported. The films were subsequently annealed in air to induce the migration and/or aggregation of the metal ions. Results of compositional and optical characterization are given, providing evidence for the successful introduction of Ag in the films, while the photoluminescence emission is strongly dependent on the annealing conditions. These films could find potential applications as downshifting layers to increase the efficiency of PV solar cells.     

Influence of Yb3+ content on microstructure and fluorescence of oxyfluoride glass ceramics containing LaF3 nano-crystals

The influence of Yb³⁺ content on structural evolution and fluorescence properties of oxyfluoride glass ceramics containing LaF₃ nano-crystals were systematically investigated. Differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) experiments indicated that Yb³⁺ ions acted as nucleating agent to facilitate LaF₃ crystallization. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) results verified the incorporation of Yb³⁺ into LaF₃ nano-crystal lattice. The absorption, emission spectra and fluorescence decays were measured. The infrared emission intensity of ⁴F_5/2 → ⁴F_7/2 transition under 980 nm excitation enhanced, while the measured lifetime reduced due to the increase of non-radiative transition probability, with the increase of Yb³⁺ content in glass ceramic. However, when Yb³⁺ doping reached 4.0 mol% the concentration quenching effect appeared.