Co-reduction synthesis of new LnxSb2−xS3 (Ln: Nd, Lu, Ho) nanomaterials and investigation of their physical properties

New Ln_xSb_2−xS₃ (Ln: Lu³⁺, Ho³⁺, Nd³⁺)-based nanomaterials were synthesized by a co-reduction method. Powder XRD patterns indicate that the Ln_xSb_2−xS₃ crystals (Ln=Lu³⁺, Ho³⁺, x=0.00−0.1 and Ln=Nd³⁺, x=0.00−0.08) are isostructural with Sb₂S₃. SEM images show that doping of Lu³⁺ and Ho³⁺ ions in the lattice of Sb₂S₃ results in nanorods while that in Nd³⁺ leads to nanoflowers. UV-vis absorption and emission spectroscopy reveal mainly electronic transitions of the Ln³⁺ ions in case of Ho³⁺ and Nd³⁺ doped nanomaterials. Emission spectra show intense transitions from excited to ground state of Ln³⁺. Emission spectra of doped materials, in addition to the characteristic red emission peaks of Sb₂S₃, show other emission bands originating from f-f transitions of the Ho³⁺ ions. TGA curves indicated that Sb₂S₃ has the highest thermal stability. The electrical conductance of Ln-doped Sb₂S₃ is higher than undoped Sb₂S₃, and increase with temperature.     

Structural studies and physical properties of novel Sm-doped Sb2Se3 nanorods

Sm³⁺ doped Sb₂Se₃ nanorods were synthesized by the co-reduction method at 180 °C and pH=12 for 48 h. Powder XRD patterns indicate that the Sm_xSb_2−xSe₃ crystals (x=0.00-0.05) are isostructural with Sb₂Se₃. The cell parameters increase for Sm³⁺ upon increasing the dopant content (x). SEM images show that doping of Sm³⁺ ions in the lattice of Sb₂Se₃ results in nanorods. High-resolution transmission electron microscopic (HRTEM) studies reveal that the Sm_0.05Sb_1.95Se₃ is oriented in the [1 0 −1] growth direction. UV-vis absorption reveals mainly electronic transitions of the Sm³⁺ ions in doped nanomaterials. Emission spectra of doped materials, in addition to the characteristic red emission peaks of Sb₂Se₃, show other emission bands originating from f-f transitions of the Sm³⁺ ions. The electrical conductance of Sm-doped Sb₂Se₃ is higher than undoped Sb₂Se₃ and increase with temperature.     

The effect of OH on IR emission of Nd, Yb and Er doped tetraphosphate glasses

Tetraphosphate glasses doped with different concentration Ln³⁺ (Ln=Nd, Yb and Er) were prepared. The IR transmission spectra and fluorescence lifetimes were measured. The relationships between IR-fluorescence decay rate and OH group content were investigated and analyzed. The constant k_OH-Ln, which represents the strength of interaction between Ln³⁺ ions and OH⁻ groups in the case of energy migration, were calculated for Nd³⁺, Yb³⁺ and Er³⁺ doped tetraphosphate glasses.     

共沉淀法制备Y2SiO5∶Er3+ ,Yb3+ ,Tm3+及其上转换发光性能研究

采用化学共沉淀法制备了系列Y_1.98-2xYb_2x Er_0.02SiO₅(0.00≤x≤0.15)以及Y_1.736Yb_0.24Er_0.02Tm_0.004SiO₅上转换发光材料,比较了室温下Y_1.98-2xYb_2x Er_0.02 SiO₅ (x=0.00,0.08)样品在400—1600 nm范围内的吸收光谱,测量了所有样品在976 nm OPO激光器激发下的上转换发射光谱,以及Er³⁺离子⁴S_3/2(⁴F_9/2)→⁴I_15/2,Tm³⁺离子¹G₄→³H₆荧光衰减曲线和不同激发功率下的上转换蓝光发射强度,从而分析讨论了Er³⁺,Tm³⁺在Y₂SiO₅中的上转换发光机理.研究结果表明:在1250 ℃相对较低的温度下合成了X2型单斜晶系Y₂SiO₅ ∶Ln³⁺(Ln³⁺=Er³⁺,Yb³⁺,Tm³⁺),Yb³⁺的敏化显著增强了样品在976 nm附近的吸收能力,并大幅度加宽了该处的吸收带.分析上转换发射光谱发现:上转换绿光和红光强度都随着Yb³⁺浓度的增加先增强后减弱,但红光的猝灭浓度较高,归因于Er³⁺→Yb³⁺反向能量传递ETU4和Yb³⁺→Er³⁺正向能量传递ETU3过程的发生;上转换蓝光发射是三光子吸收过程,是通过Yb³⁺,Tm³⁺之间三次声子辅助的能量转移方式实现的. 关键词： 上转换 共沉淀 2SiO₅∶Er³⁺')" href="#">Y₂SiO₅∶Er³⁺ 3+')" href="#">Yb³⁺ 3+')" href="#">Tm³⁺     

Novel red phosphors for solid state lighting; the system BixLn1−xVO4; Eu/Sm (Ln=Y, Gd)

Solid solutions of vanadates of formula Bi_xLn_1−xVO₄ (Ln=Y, Gd) doped with Eu³⁺ or Sm³⁺ ions have been synthesized by solid-state reactions. Intense red/orange-red luminescence is obtained in these samples on excitation in the broad charge-transfer band in the near UV. The excitation in the Eu³⁺ levels leads to much less intense red emission. These materials could find applications as red phosphors for solid-state white lighting devices utilizing GaN-based excitation in the near UV.     

Upconversion luminescence and magnetic properties of ligand-free monodisperse lanthanide doped BaGdF5 nanocrystals

Lanthanide (Ln=Yb³⁺, Er³⁺and Tm³⁺) doped monodisperse oleate-capped BaGdF₅ nanocrystals with a mean diameter of approximately 18 nm were prepared via liquid-solid-solution method. The cell parameter of the as-prepared cubic BaGdF₅ nanocrystals is 5.884 Å, which is different from the reported 6.023 Å (JCPDS 24-0098). When excited by a 980 nm laser, these Ln³⁺ doped nanocrystals exhibit multi-color up-conversion (UC) emissions including blue, yellow and white, by precisely adjusting the dopant concentration of Yb³⁺, Er³⁺ and Tm³⁺. The oleate ligands capped on the surface of the as-synthesized products, which can be conversed from hydrophobic to hydrophilic along with certain extent of weakening of UC intensity, can be moved by the acid treatment process. The measured field dependence of magnetization (M-H curves) of the BaGdF₅ nanocrystals shows excellent paramagnetism. At room temperature, the magnetization of BaGd_0.798Yb_0.2Tm_0.002F₅ nanocrystals is 0.9165 emu/g and the magnetic mass susceptibility reaches 6.11×10⁻⁵ emu g⁻¹ Oe⁻¹ at 15 kOe. Our results indicate that these bi-functional hydrophilic Ln³⁺ doped BaGdF₅ nanocrystals have potential applications in color displays, bioseparation and optical-magnetic dual modal nanoprobes in biomedical imaging.     

Optical and EPR study of BaY2F8 single crystals doped with Yb

Optical and electron paramagnetic resonance study have been carried out on BaY₂F₈ single crystals doped with Yb ions at 0.5 and 10 mol%. The crystals have been obtained using the Czochralski method modified for fluoride crystal growth. Optical transmission measurements in the range of 190-3200 nm and photoluminescence measurements were carried out at room temperature. Absorption spectra of BaY₂F₈ single crystals doped with Yb due to the ²F_7/2→²F_5/2 transitions have been observed in the 930-980 nm range. To analyze the possible presence of Yb²⁺ ions in the investigated crystals, irradiation with γ-quanta with a dose of 10⁵ Gy have been performed. The observed photoluminescence bands show usual emission in IR and other one in VIS, being an effect of cooperative emission of Yb³⁺ ions and energy up-conversion transitions of photons from IR to UV-vis(visible) due to hoping process between energy levels of paired Yb³⁺ and Er³⁺, where Er³⁺ ions are unintentional dopants. The EPR spectra of BaY₂F₈:Yb 10 mol% consist of many overlapping lines. They have been analyzed in terms of spin monomers, pairs, and clusters. The angular dependence of the resonance lines positions have been studied also to find the location of coupled ytterbium ions in the crystal structure.     

Yb3+敏化的Er3+/Ho3+共掺碲酸盐玻璃的上转换发光研究

用高温熔融法制备了系列Er³⁺/Yb³⁺共掺，Ho³⁺/Yb³⁺共掺，和Er³⁺/Yb³⁺/Ho³⁺三掺碲酸盐玻璃，在975nm激光抽运下三种掺杂玻璃中都出现了较强的绿光和红光上转换.研究了Yb³⁺离子对Er³⁺和Ho³⁺离子上转换发光强度的影响以及Yb³⁺→Er关键词： 3+/Yb³⁺/Ho³⁺共掺')" href="#">Er³⁺/Yb³⁺/Ho³⁺共掺 碲酸盐玻璃 光谱性质 上转换     

Infrared-to-visible upconversion in Er and Er/Yb activated Sb2O4 nanopowders prepared by sol-gel route

We prepared Er³⁺ doped and Er³⁺/Yb³⁺ codoped Sb₂O₄ nanocrystals by the sol-gel method. The Raman, X-ray diffraction (XRD), transmission electron microscope (TEM), and photoluminescence spectra of the samples were studied. The phonon energy of the Sb₂O₄ nanocrystals is very low (the maximum value being 461 cm⁻¹). The upconversion (UC) red emission of the Er³⁺/Yb³⁺ codoped sample is very strong at 975 nm laser diode excitation. The Sb₂O₄ nanocrystals will be a promising luminous material.     

Spectroscopic investigations of Nd-, Er-, Er/Yb-, and Tm-ions doped SiO2-Al2O3-CaF2-GdF3 glasses

This paper reports on the absorption, visible and near-infrared luminescence properties of Nd³⁺, Er³⁺, Er³⁺/2Yb³⁺, and Tm³⁺ doped oxyfluoride aluminosilicate glasses. From the measured absorption spectra, Judd-Ofelt (J-O) intensity parameters (Ω₂, Ω₄ and Ω₆) have been calculated for all the studied ions. Decay lifetime curves were measured for the visible emissions of Er³⁺ (558 nm, green), and Tm³⁺ (650 and 795 nm), respectively. The near infrared emission spectrum of Nd³⁺ doped glass has shown full width at half maximum (FWHM) around 45 nm (for the ⁴F_3/2→⁴I_9/2 transition), 45 nm (for the ⁴F_3/2→⁴I_11/2 transition), and 60 nm (for the ⁴F_3/2→⁴I_13/2 transition), respectively, with 800 nm laser diode (LD) excitation. For Er³⁺, and Er³⁺/2Yb³⁺ co-doped glasses, the characteristic near infrared emission bands were spectrally centered at 1532 and 1544 nm, respectively, with 980 nm laser diode excitation, exhibiting full width at half maximum around 50 and 90 nm for the erbium ⁴I_13/2→⁴I_15/2 transition. The measured maximum decay times of ⁴I_13/2→⁴I_15/2 transition (at wavelength 1532 and 1544 nm) are about 5.280 and 5.719 ms for 1Er³⁺ and 1Er³⁺/2Yb³⁺ (mol%) co-doped glasses, respectively. The maximum stimulated emission cross sections for ⁴I_13/2→⁴I_15/2 transition of Er³⁺ and Er³⁺/Yb³⁺ are 10.81×10⁻²¹ and 5.723×10^-21 cm². These glasses with better thermal stability, bright visible emissions and broad near-infrared emissions should have potential applications in broadly tunable laser sources, interesting optical luminescent materials and broadband optical amplification at low-loss telecommunication windows.     

Solvothermal synthesis, cubic structure and multicolor upconversion emission of ultrasmall monodisperse lanthanide-doped BaYF5 nanocrystals

Lanthanide (Ln³⁺) doped BaYF₅ (Ln=Yb³⁺, Er³⁺, Tm³⁺) nanocrystals (NCs) with a mean size of approximately 10 nm are synthesized by a solvothermal method using oleic acid as a stabilizing agent at 210 °C. The size of BaYF₅ NCs can be controlled by simply tuning the reaction parameters such as reaction temperature, reaction time and the molar ratio of F⁻/Y³⁺. The detailed structure investigation reveals that the as-synthesized BaYF₅ NCs are in the cubic structure with space group Fm3¯m instead of the reported tetragonal structure. Ln³⁺ cations occupy crystal lattice positions with lower point symmetry, which may lead to high upconversion efficiency under the excitation of a 980 nm diode laser. By adjusting the dopant concentrations of Yb³⁺, Er³⁺ and Tm³⁺, intense near-infrared, blue, yellow and white upconversion emissions are readily realized, respectively. The desirable property of the ultrasmall monodisperse NCs makes it the promising material for the applications in miniaturized solid-state light sources, multicolor three-dimensional display devices and fluorescent labels for biomedicine imaging.     

White upconversion emission and color tunability of Y2O3:R(R=Yb3+, Er3+, Tm3+) nanophosphors

The Y₂O₃:R(R = Yb³⁺, Er³⁺, Tm³⁺) nanophosphors were synthesized by a solvothermal method and the temperature dependence of the white upconversion emission was studied using a 975 nm LD. The upconversion emission spectra in 1 mol% Er³⁺/5 mol% Yb³⁺/xTm³⁺ tri-doped Y₂O₃ nanophosphors were sintered at 1000 ^°C with x from 0 to 0.5 mol%. The blue emission intensity increases increasing Tm³⁺ concentration from 0 to 0.5 mol%, because the Tm³⁺ state can be easily reached due to the ²F_7/2 → ²F_5/2 transition of Yb³⁺ near 10,000 cm⁻¹. The Y₂O₃: Er³⁺/Yb³⁺/Tm³⁺ nanophosphors exhibit upconversion emission from white to green with increasing sintering temperature. The calculated CIE coordinates are located in the white region at a pump power of 700 mW at 1000 °C, and the color coordinates were very similar to the standard white light emission. Their upconversion process was described through energy level diagrams and results of upconversion emission spectra and pump power dependence.     

Selective enhancement of green upconversion emissions of Er3+:Yb3Al5O12 nanocrystals by high excited state energy transfer with Yb3+–Mn2+ dimer sensitizing

An innovative upconversion (UC) emissions route of Er³⁺ by Yb³⁺–Mn²⁺ dimer sensitizing in Er³⁺–Mn²⁺:Yb₃Al₅O₁₂ (YbAG) nanocrystals is reported here, which resulted in the selective enhancement of green UC emission and suppression of red UC emission by a 976 nm laser diode excitation. By codoping of Mn²⁺, the green UC emission intensity increased about 260 times, while the red UC emission intensity decreased about 20 times than that of Er³⁺:YbAG nanocrystals. It indicates that the green enhancement and red suppression arise from the high excited state energy transfer with |²F_7/2, ⁴T_1g> (Yb³⁺–Mn²⁺ dimer) to the ⁴F_7/2 (Er³⁺), which partly decreases the nonradiative processes happened in the lower levels of Er³⁺. The proposed sensitizing route here may constitute a promising step to realize high-efficient UC emissions of rare-earth ions doped oxides and significantly extend their scope of applications.     

Optical properties of Er/Yb-codoped transparent PLZT ceramic

Optical absorption and emission spectra of Er³⁺/Yb³⁺ ions in PLZT (Pb_1−xLa_xZr_yTi_1−yO₃) ceramic have been studied. Based on the Judd—Ofelt (J-O) theory, the J-O intensity parameters were calculated to be Ω₂=2.021×10⁻²⁰ cm², Ω₄=0.423×10⁻²⁰ cm², Ω₆=0.051×10⁻²⁰ cm² from the absorption spectrum of Er³⁺/Yb³⁺-codoped PLZT. The J-O intensity parameters have been used to calculate the radiative lifetimes and the branching ratios for some excited ⁴I_13/2, ⁴I_11/2, ⁴I_9/2⁴F_9/2, and ⁴S_3/2 levels of Er³⁺ ion. The stimulated emission cross-section (8.24×10⁻²¹ cm²) was evaluated for the ⁴I_13/2→⁴I_15/2 transition of Er³⁺. The upconversion emissions at 538, 564, and 666 nm have been observed in Er³⁺/Yb³⁺-codoped PLZT by exciting at 980 nm, and their origins were identified and analyzed.     

Comparative study of the spectroscopic properties of Yb3+/Er3+ codoped tellurite glasses modified with R2O (R=Li,Na and K)

Spectroscopic characterization of Yb³⁺/Er³⁺ codoped TeO₂–R₂O–ZnO–Ln₂O₃ glasses as a function of network modifiers (R=Li, Na and K) has been investigated. The Judd–Ofelt parameters (Ω_t), quantum efficiency in near infrared (1.55 μm) and visible up-conversion (546 and 660 nm) and quality factor spectroscopy (χ) were calculated. Three up-conversion emission bands centered at 525, 546 and 660 nm were observed as maxima for glasses containing potassium. The measured lifetime of ⁴I_13/2, ⁴F_9/2 and ⁴S_3/2 from Er³⁺ and ⁴F_5/2 from Yb³⁺ levels increased when potassium (K) replaced lithium (Li) and Na. The maximum emission cross-section (ECS) for ⁴I_13/2→⁴I_15/2 transition of Er³⁺ was calculated to be 1.02×10^?20 cm² for TeO₂–Li₂O–ZnO–Ln₂O₃ glasses. The energy transfer efficiency (ET) from Yb³⁺ to Er³⁺, (⁴F_5/2)+(⁴I_15/2)→(⁴F_7/2)+(⁴I_13/2), was calculated using the measured lifetimes of Yb³⁺ with and without the presence of acceptor (Er³⁺). The maximum calculated ET was 58% for 0.25 mol% of Er³⁺ and 3 mol% of Yb³⁺ for TeO₂–K₂O–ZnO–Ln₂O₃ glass composition.     

Infrared, visible and upconversion emission of CaAl12O19 powders doped with Er3+, Yb3+ and Mg2+ ions

CaAl₁₂O₁₉ powders doped with Er³⁺, Yb³⁺, and Mg²⁺ ions have been prepared by a low-temperature combustion synthesis technique. Formation and chemical compositions were analysed by powder X-ray diffraction and energy-dispersive spectroscopy. The visible luminescence spectra of the doped phosphor upon excitation with ∼378 nm radiation from a Xenon lamp have been studied. A broad band emission in the range of 1400–1700 nm with a peak around 1.5 μm and FWHM of about ∼80 nm responsible for the eye-safe telecommunication window has been observed upon direct excitation with a NIR laser into the ⁴I_11/2 level of Er³⁺. The effect of co-doping with Yb³⁺ and Mg²⁺ ions in the CaAl₁₂O₁₉:Er³⁺ matrix on the photoluminescence intensity corresponding to the ²H_11/2,⁴S_3/2→⁴I_15/2, ⁴F_9/2→⁴I_15/2 and ⁴I_13/2→⁴I_15/2 transitions of Er³⁺ is elaborated and discussed in detail.     

Downconversion for the Er, Yb couple in KPb2Cl5—A low-phonon frequency host

Downconversion of a single blue/green photon to two near-infrared photons offers a promising route to increase the efficiency of photovoltaic cells. Here we report on downconversion for the well-known upconversion couple (Er³⁺, Yb³⁺) doped into a host with low (∼200 cm⁻¹) maximum phonon energy (KPb₂Cl₅). The intermediate energy level in both the upconversion and downconversion processes is the ⁴F_7/2 level around 490 nm. While fast multi-phonon relaxation to the lower energy ²H_11/2/⁴S_3/2 levels is beneficial for upconversion, it prevents efficient downconversion. To reduce multi-phonon relaxation, a low-phonon energy host (KPb₂Cl₅) was doped with Er³⁺ and varying amounts of Yb³⁺ co-dopant. The results show that downconversion from the ⁴F_7/2 level occurs, exciting two neighboring Yb³⁺ ions to the ²F_5/2 level. The efficiency is however low due to multi-phonon relaxation from the ⁴F_7/2 to the ⁴S_3/2 level via the intermediate ²H_11/2 level. Based on the results it is clear that efficient downconversion for the (Er³⁺, Yb³⁺) couple requires even lower phonon energy hosts (e.g. bromide host lattices). A Cl⁻-Yb³⁺ charge transfer absorption band is observed between 300 and 400 nm. Excitation in this band results in two broad emission bands centered around 430 and 700 nm at temperatures below 30 K, which are assigned to Cl⁻-Yb³⁺ charge transfer emission.     

Influence of carbon templates and Yb concentration on red and green luminescence of uniform Y2O3:Yb/Er hollow microspheres

Uniform Yb³⁺ and Er³⁺-codoped Y₂O₃ hollow microspheres were synthesized via urea co-precipitation using carbon spheres as templates. Intense red emission (⁴F_9/2→⁴I_15/2) and weak green emission (²H_11/2, ⁴S_3/2→⁴I_15/2) of Er³⁺ were observed for the Yb³⁺ and Er³⁺-codoped Y₂O₃ hollow microspheres under 980 nm infrared excitation. The integrated intensity of visible emission and the ratio of red to green were found to be strongly dependent on the amount of carbon sphere templates and the concentration of Yb³⁺ ions. The amount of carbon sphere templates also plays an important role in adjusting the size of crystallite. Multi-phonon relaxation resulted from the absorbents (OH⁻ and CO₃²⁻) on the surface of the crystallite, and efficient occur of energy transfer processes and cross-relaxation between Er³⁺ and Yb³⁺ are responsible for the enhancement of intensity ratio of red to green emission. Interestingly, for higher concentration of Yb³⁺ ions, the green emission is assigned to a three-phonon process in Y₂O₃:Yb/Er hollow microspheres, which also could result in the increase of the red to green emission ratio. An explanation to account for these behaviors was presented.     

Crystalline-structure-dependent green and red upconversion emissions of Er-Yb-Li codoped TiO2

Crystalline structures and infrared-to-visible upconversion luminescence spectra have been investigated in 1 mol% Er³⁺, 10 mol% Yb³⁺ and 0-20 mol% Li⁺ codoped TiO₂ [1Er10Yb(0-20)Li:TiO₂] nanocrystals. The crystalline structures of 1Er10Yb(0-20)Li:TiO₂ were divided into three parts by the addition of Yb³⁺ and Li⁺. Both green and red upconversion emissions were observed from the ²H_11/2/⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺ in Er³⁺-Yb³⁺-Li⁺ codoped TiO₂, respectively. The green and red upconversion emissions of 1Er:TiO₂ were enhanced significantly by Yb³⁺ and Li⁺ codoping, in which the intensities of green and red emissions and the intensity ratio of green to red emissions (I_green/I_red) were highly dependent on the crystalline structures. The significant enhanced upconversion emissions resulted from the energy migration between Er³⁺ and Yb³⁺ as well as the distortion of crystal field symmetry of Er³⁺ caused by the dissolving of Li⁺ at lower Li⁺ codoping concentration and the phase transformation at higher Li⁺ concentration. It is concluded that codoping with ions of smaller ionic radius like Li⁺ can efficiently improve the upconversion emissions of Er³⁺ or other rare-earth ions doped luminsecence materials.     

Er3+，Er3+/Yb3+掺杂氟化镧超微材料的光谱特性与上转换发光

采用共沉淀法制备了Er³⁺掺杂和Er³⁺/Yb³⁺共掺杂LaF₃超微材料,所制备的样品的颗粒呈球形,尺寸为250nm左右.计算得到Er³⁺单掺杂样品中对应着⁴S_3/2和⁴F_9/2能级的发光量子效率分别为67.0%和71.9%.研究发现,随着Yb³⁺离子浓度的增加 关键词： 3+')" href="#">Er³⁺ 3+')" href="#">Yb³⁺ 发光 能量传递