Enhanced red upconversion luminescence in Er-Tm codoped NaYF4 phosphor

This paper presents a study on the enhanced red upconversion (UC) luminescence via efficient energy transfer (ET) between Er3+ and Tm3+ in Er-Tm codoped NaYF4 microtubes. Er doped and Er-Tm codoped NaYF4 UC hollow microtubes have been synthesized using a hydrothermal method. Under 1560 nm excitation from a diode laser, the Er doped NaYF4 microtubes emitted dominant green UC luminescence while the Er-Tm codoped NaYF4 microtubes emitted dominant red UC luminescence, which implies the energy transfer between Er3+ and Tm3+ plays a key role in the enhanced red UC emissions. The red UC luminescence is significantly enhanced compared with the green UC luminescence with the increase of Tm3+ doping concentration. In addition, our experimental results show that the UC luminescence properties under 980 nm excitation are almost identical with that under 1560 nm excitation. Furthermore, the possible ET mechanism was proposed on the basis of our experimental results.     

Improved infrared emissions of Er(3+)-Tm3+ co-doped Al2O3 thin films: the role of cross relaxation among rare earth ions

We report the infrared emissions of Er(3+)-Tm3+ co-doped amorphous Al2O3 thin films pumped at 791 nm by a Ti:sapphire laser. The as-deposited films were annealed to improve the photoluminescence performance. Three cross relaxation channels among Er(3+)-Tm3+ and Tm(3+)-Tm3+ ions incorporated in the films were investigated as annealing temperature increases especially from 800 to 850 degrees C. In order to understand the Stark effect and cross relaxations, the photoluminescence spectra were deconvoluted by Gaussian fittings. Our results indicate that the luminescence intensity of 1.62 microm in comparison to 1.5 microm can be enhanced by the cross relaxation process [Er3+ (4I13/2) + Tm3+ (3H6) --> Er3+ (4I15/2) + Tm3+ (3F4)], and the longer-wavelength side of Er3+ emission can be improved by the CR process [Er3+ (4I15/2) + Tm3+ (3H4) --> Er3+ (4I3/2) + Tm3+ (3F4) at expense of the Tm3+ 1.47 microm emission which is also maybe quenched by the CR effect between themselves. These results suggest one possible approach to achieve broadband infrared emissions at the wavelength region of 1.45-1.65 microm from the Er(3+)-Tm3+ co-doped systems.     

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.     

Multicolor up-conversion emissions of Tm3+/Er3+/Yb3+ tri-doped YF3 phosphors

Tm3+/Er3+/Yb3+ tri-doped yttrium fluoride (YF3) phosphors were prepared by a facile hydrothermal method. X-ray topographic analysis found that the phosphors were crystallized products. Their sizes and morphologies were characterized by scanning electron microscopy (SEM, Hitachi S-4800), which indicated that most of the YF3 phosphors were hundreds of nanometers in size. Up-conversion (UC) spectra were recorded under 980-nm diode laser excitation at room temperature with a fluorescence spectrometer (Hitachi F-4500). Plenty of UC emissions of Tm3+ and Er3+ were observed from ultraviolet to red. For Tm3+ ions, a five-photon process (approximately 291 nm and approximately 347 nm), a four-photon process (approximately 362 nm and approximately 452 nm), and a three-photon process (approximately 475 nm) were identified in the UC spectra. The UC emissions from the Er3+ were: approximately 380 nm, approximately 408 nm, approximately 521 nm, approximately 537 nm, and approximately 652 nm. Therefore, cyan-white light can be observed by the naked eye at 980-nm excitation, even under low excitation power density. By comparing the UC spectra of the phosphors annealed at different temperatures, we found that the intensity of the UC luminescence increased as annealing temperature increased. Furthermore, the spectral dependencies on Tm3+ doped concentrations were studied. The energy transfer processes and fluorescence dynamics in the tri-doped system are currently being investigated.     

Upconversion luminescence enhancement in Yb3+/Tm3+-codoped Lu2O3 nanocrystals induced by doping with Li+ ions

Lutetium oxide (Lu2O3) nanocrystals doped with 2%Yb3+, 0.5%Tm3+, and various doping concentrations of Li+ (0, 3, 5, 7, 10, 12, and 15 mol%) were prepared by the sol-gel method. The dependence on different doping concentrations of Li+ ions of the structure, morphology, and the upconversion emission intensity of the Lu2O3:2%Yb3+, 0.5%Tm3+ nanocrystals was investigated. The obtained Lu2O3 nanocrystals were systematically characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), Fourier transformed infrared (FT-IR) spectra, Raman spectra, and upconversion spectra measurements. It was found that all the nanocrystals can be readily indexed to pure cubic phase of Lu2O3, indicating good crystallinity. The experimental results show that Li+ doping in Lu2O3:2%Yb3+, 0.5%Tm3+ nanocrystals can greatly enhance the upconversion emission intensity. The strong blue (490 nm) and the weak red (653 nm) emissions from the prepared nanocrystals were observed under 980 nm laser excitation, and attributed to the 1G4 --> 3H6 and 1G4 --> 3F4 transitions of Tm3+ ions, respectively. An simple analysis based on steady-state rate equations and a power-dependent study both indicate that the 1G4 levels can be populated by three-step energy transfer (ET) processes. The enhancement of the upconversion luminescence was suggested to be the consequence of the modification of the local field symmetry around the Tm3+ ion, reduced number of OH- groups, and the enlarged nanocrystal size induced by the Li+ ions.     

Optical high temperature sensor based on enhanced green upconversion emissions in Er3+-Yb3+-Li+ codoped TiO2 powders

The Er3+-Yb3+-Li+ codoped TiO2 powders have been prepared by sol-gel method. The strong enhancement of green and red upconversion emissions were obtained for Er3+-Yb3+ codoped TiO2 by additional Li+ codoping and investigated using 976 nm semiconductor laser diode excitation. The enhanced upconversion emissions by the addition of Li+ resulted from the formation of Li compound with lower crystal field symmetry. The fluorescence intensity ratio (FIR) of green upconversion emissions from the transitions of 2H(11/2) --> 4I(15/2) and 4S(3/2) --> 4I(15/2) of Er3+ in the Er3+-Yb3+-Li+ codoped TiO2 has been studied as a function of temperature in the range of 300-925 K, and the maximum sensitivity was determined to be 0.0025 K(-1). Er3+-Yb3+-Li+ codoped TiO2 material with the highest operating temperature up to 925 K, has higher temperature sensitivity and fluorescence efficiency being a promising candidate for applications in optical high temperature sensor.     

Tm3+/Ho3+共掺硫卤玻璃的2.00μm荧光特性研究

通过真空熔融淬冷法制备了不同浓度Tm3+/Ho3+离子共掺的70GeS2-20In2S3-10CsI玻璃样品,分析了样品的热稳定性及拉曼光谱,测试了样品的吸收光谱以及808 nm激光泵浦下Ho3+:5I7→5I8辐射跃迁对应的2.00μm荧光光谱特性.结果表明:Tm3+离子掺杂浓度为0.25mol%时,随着Ho3+离子掺杂浓度从0.05mol%增加到0.125mol%,Tm3+离子在1.86μm的发光强度逐渐减弱,Ho3+离子2.00μm荧光明显增强,表明Tm3+/Ho3+离子之间存在有效的能量转移.     

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.     

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 luminescence properties of lanthanide (III)-doped YF3 nanoparticles

Synthesis process and luminescence properties of trivalent lanthanide ions (Ln3+) doped YF3 nanoparticles have been investigated. To synthesis Ln(3+)-doped YF3 nanoparticles, the mixture of (YCl3 x nH2O + LnCl3 x nH2O), and NH4F was hydrothermal treated at 180 degrees C in a Teflon-liner auto-clave or heated at higher temperatures (400 degrees C - 600 degrees C) in a stove. The XRD patterns showed that the Ln(3+)-doped orthorhombic YF3 nanoparticles with no second phase have been prepared. The solid solution Y(1-x)Eu(x)F3 (x = 0 - 0.4) nanoparticles have been synthesized. The luminescence concentration quenching resulted from resonance energy transfer between neighboring Eu3+ ions occurred at higher Eu3+ concentrations (30 mol%). The upconversion luminescence of Er(3+)-Yb3+ codoped YF3 nanoparticles under 980 nm excitation has also been observed. With increase of heated temperature, the size of the Er(3+)-Yb3+ codoped YF3 nanoparticles increased gradually, and upconversion luminescence intensity increased significantly.     

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.     

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.     

White luminescence by up-conversion from thin film made with Ln(3+)-doped NaYF4 nanoparticles

White light-emitting thin films containing Ln(3+)-doped NaYF4 nanoparticles were prepared by a simple spin-coating method. White light was generated by two different lanthanide ions, Er3+ (red and green) and Tm3+ (blue), by upconversion process under the excitation of a 980-nm laser diode. The ratio of the intensity of the three main emissions was tuned by controlling the concentration of the nanoparticles in the thin film and the concentration of the lanthanide ions in the nanoparticles. The color coordinates corresponding to emissions of different nanoparticle concentrations and with the different pump powers were investigated. When the pump power was fixed at 900 mW, the thin film with a concentration ratio of 2.5:1 emitted pure white light with coordinates of (0.333, 0.339).     

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.     

Luminescence and energy transfer characteristics of Ce3+- and Tb3+-codoped nanoporous 12CaO 7Al2O3 phosphors

The novel green-emitting phosphors of 12CaO 7Al2O3:Ce3+ , Tb3+ (C12A7:Ce3+, Tb3+) were synthesized by a solid-state reaction. Upon the excitation of Ce3+ at 350 nm, the C12A7:Ce3+, Tb3+ phosphor shows intense green emissions located at 543 nm assigning to 5D4-7F5 transitions of Tb3+ ions, and weak blue emissions centered at 434 nm due to the transitions of Ce3+ 5d-4f. The photoluminescence (PL) intensity of Ce3+ decrease with increasing Tb3+ concentration, indicating the effective energy transfer (ET) occurred from Ce3+ to Tb3+ in C12A7:Ce3+, Tb3+. The ET efficiency between Ce3+ and Tb3+ in the optimum composition reaches to 99%. Based on Dexter's ET theory, we have demonstrated that the efficient ET is a resonant type via dipole-dipole mechanism with an energy transfer critical distance of 4.02 A. Our results suggested that C12A7:Ce3+, Tb3+ phosphor would be a promising green-emitting phosphor for UV-converting white light-emitting diodes.     

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.     

Anneal temperature dependent Er/Tm energy transfer and luminescence from Er and Tm co-doped silicon-rich silicon oxide

The effect of the anneal temperature on the Er³⁺/Tm³⁺ energy transfer and subsequent Er³⁺/Tm³⁺ luminescence from Er/Tm co-doped, silicon-rich silicon oxide films are investigated. The anneal procedure necessary for optimum photoluminescence (PL) from the co-doped film is substantially different from that for only Er- or Tm-doped films. Analysis and modeling of PL intensity and time-resolved PL indicate that this higher optimum anneal temperature is due to the anneal temperature dependent Er-Tm interactions. In addition, the optimization of combined ultrabroad Er/Tm luminescence was discussed controlling Er-Tm interactions which is tailored by the change of Er/Tm doping ratio and anneal temperature.     

Er3+ 掺杂对Bi3Ti1.5W0.5O9-Bi4Ti3O12 共生无铅压电陶瓷性能的影响

用传统固相法制备了Bi_7-x Er _x Ti_4.5W_0.5O₂₁(BTW-BIT-xEr³⁺,x=0.05、0.10、0.15、0.25、0.35)共生铋层结构无铅压电陶瓷,用BTW-BIT-xEr³⁺的XRD和SEM表征其相结构和形貌,研究了Er³⁺掺杂对其上转换发光性能和电学性能的影响。结果表明：在这种陶瓷中生成了铋层状结构的单一晶相。在980 nm光波激发下所有组分的上转换荧光谱中都能清晰地观察到两个绿光和一个红光发射峰,峰的中心分别位于532 nm、548 nm和660 nm处。改变掺杂Er³⁺离子浓度可调节其强度比。根据BTW-BIT-0.15Er³⁺样品在532 nm和548 nm绿光的光强比拟合了290~440 K的温度灵敏度,结果表明440 K处的灵敏度最大为0.0023 K^-1。Er³⁺离子替代BTW-BIT-xEr³⁺伪钙钛矿层的Bi³⁺使氧空位浓度的降低,降低了高温介电损耗,提高了激活能和压电常数。BTW-BIT-0.15Er³⁺陶瓷的综合电学性能最优,分别为d₃₃=14 pC/N、T_c=697℃,tanδ=0.53%、Q_m=2055。这种陶瓷材料具有最优的发光性能和良好的热稳定性。     

Infrared-to-green up-conversion in Er3+, Yb3+-doped monoclinic KGd(WO4)2 single crystals

Optical spectroscopy of the green emission of erbium in KGd(WO₄)₂ (KGW) single crystals codoped with ytterbium ions is investigated. To do this, we firstly grew good-optical-quality KGW single crystals doped with Er³⁺ and Yb³⁺ at several dopant concentrations by the Top-seeded-solution-growth slow-cooling method (TSSG). Green photoluminescence of Er³⁺ in KGW host was studied at room temperature (RT) and low temperature (10 K) by means of Yb³⁺ sensitization after infrared excitation at 981 nm (10194 cm⁻¹). We calculated the emission and gain cross-sections and compared these with those of other known Er³⁺-doped laser materials like LiYF₄ :Er (YLF:Er) and Y₃Al₅O₁₂:Er (YAG:Er) at RT. Our study also focused on determining the optimal concentration of ions for generating the most intense green emission. We measured the lifetime of the green emission after infrared pump at several Yb³⁺ concentrations. From the low-temperature emission experiments, we determined the energy position of the sublevels of the ground state of erbium.