Microstructure and environment dependence of 2H11/2 --> 4I15/2 upconversion emission in YVO4:Er3+, Yb3+ nanocrystals

Upconversion emission of different nanocrystalline YVO4:Er3+, Yb3+ synthesized by a hydrothermal process at low temperature was studied under 980 nm excitation where green [(2H11/2, 4S3/2) --> 4I15/2] and red (4F9/2 --> 4I15/2) emissions demonstrate sensitivity to the local environments of Er3+. Small particle size, high Yb3+ concentration, or high temperature favors the emission of the 2H11/2 --> 4I15/2 transition. Both XRD patterns and Raman spectra have confirmed that crystal lattice distortion of YVO4:Er3+, Yb3+ nanocrystals is more serious when the nanoparticle size is decreasing or Yb3+ concentration is increasing. This distortion is thought to play a key role in the observed spectral properties, which might lead to a new route to improve the monochromatic upconversion emission efficiency in these nanocrystals.     

Controllable multicolor upconversion luminescence of lanthanide doped NaGdF4 nanocrystals through single laser excitation at 980 nm

Room temperature multicolor Upconversion (UC) luminescence in Yb3+, Tm3+, Er3+ ions doped NaGdF4 nanocrystals have been successfully synthesized by a hydrothermal method. As-prepared nanocrystals are highly crystalline and well-dispersed in cyclohexane to form stable and clear colloidal solutions, which demonstrates strong emission properties with a single laser excitation at 980 nm. The multicolor light consists of blue, green, and red UC radiations that correspond to transitions 1G4 --> 3H6 of Tm3+, 2H(11/2)/4S(3/2) --> 4I(15/2), and 4F(9/2) --> 4I(15/2) of Er3+ ions, respectively. The UC mechanisms were proposed based on spectral, kinetic, and pump power dependence analyses.     

Upconversion in NaYF(4):Yb, Er nanoparticles amplified by metal nanostructures

Upconversion (UC) fluorescence in NaYF(4):Yb, Er nanoparticles amplified by metal nanostructures was compared in two nanostructure geometries: gold nanoshells surrounding nanoparticles and silver nanostructures adjacent to the nanoparticles, both placed on a dielectric silica surface. Enhanced UC luminescence signals and modified lifetimes induced by these two metals were observed in our study. The UC luminescence intensities of green and red emissions were enhanced by Ag nanostructures by a factor of approximately 4.4 and 3.5, respectively. The corresponding UC lifetimes were reduced ～ 1.7-fold and ～ 2.4-fold. In NaYF(4):Yb, Er nanoparticles encapsulated in gold nanoshells, higher luminescence enhancement factors were obtained (～9.1-fold for the green emission and ～ 6.7-fold for the red emission). However, the Au shell coating extended the red emission by a factor of 1.5 and did not obviously change the lifetime of green emission. The responsible mechanisms such as plasmonic enhancement and surface effects are discussed.     

Emission properties of hydrothermal Yb(3+), Er(3+) and Yb(3+), Tm(3+)-codoped Lu2O3 nanorods: upconversion, cathodoluminescence and assessment of waveguide behavior

Yb(3+) and Ln(3+) (Ln(3+) = Er(3+) or Tm(3+)) codoped Lu(2)O(3) nanorods with cubic Ia3 symmetry have been prepared by low temperature hydrothermal procedures, and their luminescence properties and waveguide behavior analyzed by means of scanning near-field optical microscopy (SNOM). Room temperature upconversion (UC) under excitation at 980 nm and cathodoluminescence (CL) spectra were studied as a function of the Yb(+) concentration in the prepared nanorods. UC spectra revealed the strong development of Er(3+) (4)F(9/2) → (4)I(15/2) (red) and Tm(3+) (1)G(4) → (3)H(6) (blue) bands, which became the pre-eminent and even unique emissions for corresponding nanorods with the higher Yb(3+) concentration. Favored by the presence of large phonons in current nanorods, UC mechanisms that privilege the population of (4)F(9/2) and (1)G(4) emitting levels through phonon-assisted energy transfer and non-radiative relaxations account for these observed UC luminescence features. CL spectra show much more moderate development of the intensity ratio between the Er(3+) (4)F(9/2) → (4)I(15/2) (red) and (2)H(11/2), (4)S(3/2) → (4)I(15/2) (green) emissions with the increase in the Yb(3+) content, while for Yb(3+), Tm(3+)-codoped Lu(2)O(3) nanorods the dominant CL emission is Tm(3+) (1)D(2) → (3)F(4) (deep-blue). Uniform light emission along Yb(3+), Er(3+)-codoped Lu(2)O(3) rods has been observed by using SNOM photoluminescence images; however, the rods seem to be too thin for propagation of light.     

Ultraviolet upconversion fluorescence of Er3+ in Yb3+/Er3+-codoped Gd2O3 nanotubes

Under 980 nm excitation, room-temperature ultraviolet (UV) upconversion (UC) emissions of Er3+ from the 4G(9/2), 2K(13/2), and 2P(3/2) states were observed in Gd2O3:Yb3+/Er3+ nanotubes, which were synthesized via a simple wet-chemical route at low temperature and ambient pressure followed by a subsequent heat treatment at 800 degrees C. The experimental results exhibited that these UV emissions came from four-photon UC processes. In the Gd2O3:Yb3+/Er3+ nanocrystals, the energy transfers (ETs) from Yb3+ to Er3+ played important roles in populating the high-energy states of Er3+ ions. This material provides a possible candidate for building UV compact solid-state lasers or fiber lasers.     

The properties of upconversion luminescence on YAIO3:Er(3+) nanophosphors with different Er(3+) concentrations

We report the properties of upconversion luminescence on Yttrium aluminum perovoskite (YAIO3) doped with trivalent erbium at concentrations of 1, 2, 3, 5 and 7 mol%. The samples were synthesized by solvo-thermal reaction method and the XRD patterns conforms that the YAP:Er(3+) nanophosphors have orthorhombic phase. Efficient green and red upconversion (UC) emission of YAP:Er(3+) nanophosphors was measured under the excitation of 975 nm continuous wave diode laser, and its dynamics and pump power dependence were investigated. As concentration of Er(3+) ion increased from 1 to 7 mol%, the red UC emission increased more rapidly. It is attributed to the energy transfer (4I(11/2) --> 4I(15/2):4I(13/2) --> 4F(9/2)) and to the cross relaxation (4S(3/2) --> 4I(9/2):4I(15/2) --> 4I(13/2)) between Er(3+) ions. In this case, the green and red emissions were yielding from quadratic to linear. These conclusions obtained are confirmed by theoretical investigations based on steady-state rate equations.     

Fabrication and up-conversion luminescence of Er3+:Y2O3 nanoparticles

Y2O3 nanoparticles doped with different concentrations of Er3+ were prepared by the co-precipitation method. X-ray diffraction and transmission electron microscopy results show that Er3+ dissolves completely in the Y2O3 cubic phase. The Er3+:Y2O3 nanoparticles are homogeneous in size and nearly spherical, and the average diameter of the particles after being calcined at 1,000 degrees C for 2 h is in the range of 40-60 nm. When Er3+:Y2O3 nanoparticles are excited under a 980 nm diode laser, there are two main emission bands: green emission centered at 562 nm corresponding to the 4S3/2/2H11/2 --> 4115/2 radiative transitions and red emission centered at 660 nm corresponding to the 4F9/2 --> 4I15/2 radiative transitions. By changing the doping concentration of Er3+ ions, the up-conversion luminescence can be gradually tuned from green to red.     

Ba5Zn4Y8O21:Ho^3+,Yb^3+上转换发光粉的制备与发光性能研究

为实现以Ba5Zn4Y8O21为基质的上转换三基色发光,采用固相合成法于1200℃下制备了Ba5Zn4Y8O21:Ho^3+,Yb^3+发光粉,并对其绿光发射特性进行了研究。980 nm激发下的上转换发射光谱测试结果证实,最佳掺杂浓度下的Ba5Zn4Y8O21:14%Yb^3+,0.15%Ho^3+主要呈现5S2/5F4→5I8跃迁所致的548、553 nm绿光发射,而5F5→5I8和5S2/5F4→5I7跃迁产生的664、758nm红光和近红外光发射非常微弱。而且,绿光强度随激发功率呈线性变化,在20.7 mW/cm^2功率密度范围内,绿红光分支比最高达13.16,呈现优异的色纯度。上转换发光热稳定性测试结果表明,样品的发光效率随样品温度的升高略有下降,50℃时发光强度降低仅9.75%。上述结果证实,Ba5Zn4Y8O21:Ho^3+,Yb^3+是一种优质的绿光上转换发光材料。     

P2O3-B2O3-Al2O3-SrO-BaO玻璃中Yb3+非辐射能量转移下Er3+离子的增强发射

本文研究了共掺Er3 +/Yb3 +P2 O3 -B2 O3 -Al2 O3 -SrO -BaO玻璃的能量转移过程。实验中制备了高掺杂Yb3 +离子的双掺Er3 +/Yb3 +的磷酸盐玻璃样品。在Er3 +/Yb3 +掺杂比率 >1 :1 8(mol% )时 ,观测到了基于Yb3 +离子至Er3 +离子能量转移下Er3 +( 4 I13 / 2 →4I15 / 2 )的增强发射和Yb3 +( 2 F7/ 2 →2 F5 / 2 )发射的减弱 ,当Yb3 +离子掺杂浓度超过 2 .1× 1 0 2 1ions/cm3 时 (Er3 +/Yb3 +≤ 1 :1 8,mol% ) ,由于Yb3 +离子的自淬灭效应 ,Er3 +离子的发射强度降低。实验中得到了Yb3 +离子的最佳掺杂浓度为1 .74× 1 0 2 1ions/cm3     

Synthesis and characterization of Y2O3:Er3+ upconversion materials with nanoporous structures

Y2O3:Er3+ upconversion materials with nanoporous structures were prepared by a hydrothermal method following a post-thermal treatment. The structure and morphology of the materials were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). The results indicated that the as-obtained Y2O3:Er3+ powders were of cubic-phase structure, and the nanoporous structure was formed in the annealing process. The optical results indicated that high annealing temperature could improve the upconversion properties, but it could destroy the nanoporous structure. Under 980 nm excitation, red (4F(9/2) --> 4I(15/2) and green (2H(11/2), 4S(3/2) --> 4I(15/2)) upconversion luminescence was observed. The studies on the intensity dependence of upconversion emission indicated that two-photon processes were responsible for the green and red upconversion luminescence. This kind of multifunctional material has potential applications in nanocontainers for use as biomolecule and drugs carriers.     

Luminescence properties and excitation process of a near-infrared to visible up-conversion color-tunable phosphor

Further investigation of previously reported color-tunable NaNbO₃-based up-conversion phosphor doped with Er³⁺, Yb³⁺, and Al³⁺ (NaNbO₃:Er,Yb,Al) was undertaken. Color tuning is achieved by variation of the relative intensity of the red/green emission, which is dependent on the pulse width of the near-infrared (980 nm) excitation. The chromaticity of emissions ranging from green to reddish-yellow with a change of pulse duration from 50 to 2400 μs is wider than that of the reference compound LaGaO₃:Er,Yb, and is not influenced by the excitation intensity. It was elucidated that the green and red emissions occur via different excitation routes, of which the latter is characterized by a much slower build-up of emission.     

Investigation on Yb3+∕Er3+∕Tm3+ tri-doped phosphate glass ceramic for white-light-emitting diode

Yb3+∕Er3+∕Tm3+ tri-doped phosphate glass ceramics were prepared by a high-temperature melting method and thermal treatment technology. Upconversion (UC) emissions of the Yb3+∕Er3+∕Tm3+ tri-doped phosphate glass ceramic samples were studied under 975 nm excitation. The glass ceramic samples can simultaneously generate blue, green, and red emissions. The multicolor emission obtained was tuned to white light by adjusting the Er3+ ion concentration. The emission color of the sample doped with 8 mol.% Er3+ ion is white to the naked eye, and CIE coordinates (x=0.316, y=0.354) of the sample are close to the standard equal energy white-light illumination (x=0.333, y=0.333). The material will be useful in developing the white-light-emitting diode.     

铒单掺和铒/镱共掺氟氧玻璃的上转换发光性质研究

研究了室温下掺不同摩尔分数Er3+单掺和Er3+/Yb3+双掺的20GaF3-15InF3-17CdF2-15ZnF2-10SnF2-3P2O5-(20-x-y)PbF2-xErF3-yYbF3(x=0.1~0.4,y=1~4)氟氧玻璃的上转换发光性质。755nm激发下,在Er3+单掺系列玻璃中观察到紫色(410nm)、蓝色(465nm)和绿色(522nm、544nm)上转化发光,随着掺杂Er3+浓度的增大,各荧光强度增幅有变缓的趋势。980nm激发下,由于Yb3+的敏化作用,在Er3+/Yb3+双掺系列玻璃中观察到绿色(548nm、527nm)和红色(661nm)上转换发光,固定Er3+浓度,随着Yb3+浓度的增大,各荧光强度先增大后减小,当Yb3+、Er3+掺杂浓度比为15时发光强度最大。该氟氧玻璃具有比氟化物玻璃更好的抗析晶稳定性,掺稀土离子后在不同波长激发下可观察到明亮的红、绿色上转换荧光,是一种有潜质用于红、绿色上转换发光的材料。     

Er3+ -doped anatase TiO2 nanocrystals: crystal-field levels, excited-state dynamics, upconversion, and defect luminescence

A comprehensive survey of electronic structure and optical properties of rare-earth ions embedded in semiconductor nanocrystals (NCs) is of vital importance for their potential applications in areas as diverse as luminescent bioprobes, lighting, and displays. Er3+ -doped anatase TiO2 NCs, synthesized via a facile sol-gel solvothermal method, exhibit intense and well-resolved intra-4f emissions of Er3+ . Crystal-field (CF) spectra of Er3+ in TiO2 NCs are systematically studied by means of high-resolution emission and excitation spectra at 10-300 K. The CF analysis of Er3+ assuming a site symmetry of C(2v) yields a small root-mean-square deviation of 25.1 cm(-1) and reveals the relatively large CF strength (549 cm(-1) ) of Er3+, thus verifying the rationality of the C(2v) symmetry assignment of Er3+ in anatase TiO2 NCs. Based on a simplified thermalization model for the temperature-dependent photoluminescence (PL) dynamics from (4) S(3/2) , the intrinsic radiative luminescence lifetimes of (4) S(3/2) and (2) H(11/2) are experimentally determined to be 3.70 and 1.73 μs, respectively. Green and red upconversion (UC) luminescence of Er3+ can be achieved upon laser excitation at 974.5 nm. The UC intensity of Er3+ in Yb/Er-codoped NCs is found to be about five times higher than that of Er-singly-doped counterparts as a result of efficient Yb3+ sensitization and energy transfer upconversion (ETU) evidenced by its distinct UC luminescence dynamics. Furthermore, the origin of defect luminescence is revealed based on the temperature-dependent PL spectra upon excitation above the TiO2 bandgap at 325 nm.     

Er3+/Yb3+掺杂NaGd(WO4)2粉体的制备与发光性能

采用水热法成功制备了Er~(3+)/Yb~(3+)双掺杂的NaGd(WO_4)_2纳米粉体,研究了不同络合剂、水热温度对样品形貌和结构的影响。测量了不同Er~(3+)掺杂浓度样品的可见上转换和近红外发射光谱。结果表明:在980nm LD激发下,可观测到样品强烈的绿色上转换发光,对应Er~(3+)的~2H_(11/2)→~4I_(15/2)(530nm)和~4S_(3/2)→~4I_(15/2)(552nm)跃迁,以及较弱的红色上转换和近红外发光,分别对应Er~(3+)的~4F_(9/2)→4I15/2(656nm)和~4I_(13/2)→~4I_(15/2)(1 532nm)跃迁。且随着Er~(3+)掺杂浓度的增加,样品的上转换红绿光和1.54μm附近的近红外光均呈现出先增大后减小的趋势。样品的激发和发射光谱显示,在378nm处的激发峰最强,对应Er~(3+)的~4I_(15/2)→~4 G_(11/2)能级跃迁,最强发射峰位于552nm。根据泵浦功率与发光强度的关系可以得出,红光和绿光的发射主要为双光子吸收过程,但红光还包含了一定的单光子吸收成分。     

Sensitized upconversion emissions of Tb3+ by Tm3+ in YF3 and NaYF4 nanocrystals

Yb3+-Tm3+-Tb3+-codoped YF3 and NaYF4 nanocrystals (NCs) were synthesized using a simple hydrothermal method. Under 980 nm excitation, violet and ultraviolet upconversion (UC) emissions of 5D3 --> 7FJ (J = 6, 5, 4) and 5D4 --> 7FJ (J = 6, 5, 4, 3) of Tb3+ ions were observed with the fluoride NCs. In the Yb-Tm-Tb codoped NCs, energy transfer (ET) processes from Tm3+ to Tb3+ were proposed to be the main mechanisms for the UC emissions of Tb3+ ions. They are more efficient than the phonon assisted cooperative sensitization of the Yb3+ couple proposed previously for similar material system. The analysis of power dependence indicated that populating the 5D4 level of the Tb3+ ions was a four photon UC process, which demonstrated the existence of the two step ET process of Yb3+ --> Tm3+ --> Tb3+. It was also found that UC luminescence properties of Tb3+ ions were sensitive to crystal structures.     

White up-conversion luminescent property in Re3+:Gd3Ga5O12 nanocrystals

Rare-earth ions doped Gd3Ga5O12 nanocrystals have been prepared by a propellant combustion synthesis method and their up-conversion properties were systematically investigated in this paper. XRD, SEM, TEM, and up-conversion emission spectra were used to characterize the synthesized nanocrystals. Energy transfer from Yb3+ to Er3+ and Tm3+ can occur simultaneously in the as-synthesized Gd3Ga5O12 nanocrystals. The up-conversion mechanisms and relevant energy transfer processes are discussed. A white light generation was observed when the Yb3+, Er3+ and Tm3+ were directly incorporated in the Gd3Ga5O12 lattice. And its calculated color coordinates is (0.35, 0.41) under the excitation at 974.5 nm. The bright white luminescent nanocrystals may have potential application in the field of lighting, displays and photonics.     

Efficient dual mode multicolor luminescence in a lanthanide doped hybrid nanostructure: a multifunctional material

The present work deals with inorganic-organic hybrid nanostructures capable of producing intense visible emission via upconversion (UC), downconversion (DC), and energy transfer (ET) processes which show the potential of the material as a luminescent solar collector (LSC), particularly to improve the efficiency of silicon solar cells. To achieve this, Gd2O3:Yb3+/Er3+ phosphor (average particle size～35 nm) and a Eu(DBM)3Phen organic complex have been synthesized separately and then the hybrid structure has been developed using a simple mixing procedure. Intense UC emission (in the red, green, and blue regions) due to Er3+ is observed on near infrared (976 nm) excitation which shows color tunability with input pump power. In contrast, intense red emission of Eu3+ is observed on ultaviolet (UV) (355 nm) excitation. The feasibility of energy transfer from Er3+ ions to Eu3+ ions has also been noted. These excellent optical properties are retained even if the particles of the hybrid nanostructure are dispersed in liquid medium, which also makes it suitable for security ink purposes.     

Intense red upconversion emission of Yb/Tm/Ho triply-doped tellurite glasses

By conventional melting and quenching methods, 3Yb2O3-0.2Tm2O3-xHo2O3 (wt%, x=0.2~1.2) was doped into an easily fiberized tellurite glass with composition of 78TeO2-10ZnO-12Na2O (mol%) to form YTH-TZN78 glasses. Under 976 nm excitation, the direct sensitizing effect of Yb ions (Yb→Ho) and indirect sensitizing and self-depopulating effects of Tm ions (Yb→Tm→Ho) were found to present intense red upconversion emission at 657 nm (Red, Ho:5F5→5I8) and were responsible for the absence of the usually observed 484 nm emission (Blue, Tm:1G4→3H36). Regardless of the dopant concentration of Ho ions, the intensity of the red emission at 657 nm (Red, Ho:5F5→5I8) is about three times stronger than that of the green one at 543 nm (Green, Ho:5S2→5I8). For this certain red emission at 657 nm, 0.4 wt% Ho2O3-doped YTH-TZN78 glass was found to present the highest emission intensity and is therefore determined as a promising active tellurite glass for red fiber laser development.     

Preparation and upconversion luminescence of Y2SiO5:Yb3+, Ho3+ nanophosphors

X1 type monoclinic Y2SiO5:Yb3+, Ho3+ nanophosphors with fixed (varied) Ho3+ and varied (fixed) Yb3+ concentrations were synthesized by sol-gel method. The nanophosphors presented lacunaris shape with an average size of about 47 nm measured by transmission electron microscopy and scanning electron microscopy. Up-conversion emissions have been observed at 550 nm corresponding to (5F4, 5S2)-5I8 transition and 661 nm due to 5F5-5I8 transition of Ho3+ upon 980 nm excitation at room temperature. The results indicate that both green and red luminescences are based on the two-photon process through the energy transfer from Yb3+. However, the intensity of green emission is weaker than that of the red, because the 5I7 level of Ho3+ can be effectively populated. The integrated upconversion emission intensity on the Yb3+ and Ho3+ concentrations were also studied.