Effect of Yb concentration on the structures and upconversion luminescence properties of Y2O3:Er ultrafine phosphors

Y₂O₃:Er³⁺ ultrafine phosphors with a varying Yb³⁺ ion concentration were prepared by a urea homogeneous precipitation method. The results of XRD show that all the samples are of a pure cubic structure and the average crystallite sizes can be calculated as 45, 34, and 28 nm for Y₂O₃:Er³⁺ ultrafine phosphors with Yb³⁺ ion concentrations of 0, 10%, and 20%, respectively. The lattice constant and cell volume of the ultrafine phosphors decrease with enhancing Yb³⁺ ion concentration. The upconversion luminescence spectra of all the samples were studied under 980 nm laser excitation. The strong green and red upconversion emission were observed, and attributed to the ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺, respectively. The intensity of red emission increases with increasing Yb³⁺ ion concentration. The effect of Yb³⁺ ion concentration on the structures and upconversion luminescence mechanism were discussed.     

Spectroscopic properties of Yb and Er ions in heavy metal glasses

Selected heavy metal glasses containing Yb³⁺ and Er³⁺ ions have been studied. Near-infrared luminescence spectra at 1.53 μm and up-conversion spectra of Er³⁺ ions were registered under excitation of Yb³⁺ ions by 975 nm diode laser line. The luminescence bands correspond to ⁴I_13/2-⁴I_15/2 (NIR), ⁴S_3/2-⁴I_15/2 (green) and ⁴F_9/2-⁴I_15/2 (red) transitions of Er³⁺, respectively. The optical transitions of rare earth ions have been examined as a function of glass host. The unusual large spectral linewidth nearly close to 110 nm for ⁴I_13/2-⁴I_15/2 transition of Er³⁺ ions in Yb-Er co-doped lead borate glass was obtained, whereas long-lived NIR luminescence at 1.53 μm was detected in lead germanate glass. The NIR luminescence and up-conversion phenomena strongly depend on stretching vibrations of glass host, which was confirmed by FT-IR spectroscopy.     

White light emission in Tm/Er/Yb tri-doped Y2O3 transparent ceramic

Tm³⁺/Er³⁺/Yb³⁺ triply doped Y₂O₃ transparent ceramics were fabricated by solid state reaction and characterized from the point of view of white light upconversion luminescence. All the samples exhibited high transparency not only in near-infrared band but also in visible region. Strong red (Er³⁺: ⁴F_9/2 → ⁴I_15/2), green (Er³⁺: ²H_11/2, ⁴S_3/2 → ⁴I_15/2) and blue (Tm³⁺: ¹G₄ → ³H₆) upconversion emissions have been observed under 980 nm excitation at room temperature. By varying the concentration of Er³⁺ ion, various colors of upconversion luminescence (pure blue, bluish green, pure green and yellowish green), including white light with CIE-X = 0.295 and CIE-Y = 0.312, can be easily achieved.     

Luminescence properties of red-emitting Ca<Subscript>2</Subscript>Al<Subscript>2</Subscript>SiO<Subscript>7</Subscript>:Eu<Superscript>3+</Superscript> nanoparticles prepared by sol-gel method

A series of red-emitting Ca2-xAl2SiO7:xEu3+(x = 1 mol.%-10 mol.%) phosphors were synthesized by the sol-gel method.The effects of annealing temperature and doping concentration on the crystal structure and luminescence properties of Ca2Al2SiO7:Eu3+ phosphors were investigated.X-ray diffraction(XRD) profiles showed that all peaks could be attributed to the tetragonal Ca2Al2SiO7 phase when the sample was annealed at 1000℃.Scanning electron microscopy(SEM) micrographs indicate that the phosphors have an irregularly rounded morphology with particles of about 200 nm.Excitation spectra showed that the strong broad band at around 258 nm and weak sharp lines in 350-490 nm were attributed to the charge transfer band of Eu3+-O2-and f-f transitions within the 4f6 configuration of Eu3+ ions,respectively.Emission spectra implied that the red luminescence could be attributed to the transitions from the 5D0 excited level to the 7FJ(J = 0,1,2,3,4) levels of Eu3+ ions with the main electric dipole transition 5D0→7F2(618 and 620 nm),and Eu3+ ions prefer to occupy a lower symmetry site in the crystal lattice.Moreover,the photoluminescence(PL) intensity was strongly dependent on both the sintering temperature and doping concentration,and the highest PL intensity was observed at an Eu3+ concentration x = 7 mol.% after annealing at 1100℃.The obtained Ca2Al2SiO7:Eu3+ phosphor may have potential application for the red lamp phosphor.     

Upconversion luminescence in Er/Yb codoped Y2CaGe4O12

Calcium yttrium tetrametagermanates Y₂CaGe₄O₁₂ doped with Er³⁺ and Er³⁺/Yb³⁺ reveal upconversion emission in visible spectral range under near-infrared excitation, λ_ex = 980 nm. For the solid solution Er_xY_2−xCaGe₄O₁₂ concentration dependencies for the green and red lines of the visible emission around 526 nm (²H_11/2 → ⁴I_15/2), 545 nm (⁴S_3/2 → ⁴I_15/2) and 670 nm (⁴F_9/2 → ⁴I_15/2) show the optimal value for the sample x = 0.2. The power dependence of the visible luminescence measured at room temperature in the low-power limit indicates two-photon upconversion process. Direct intensification of the upconversion emission signals has been achieved by ytterbium sensitizing. The other upconversion excitation mechanism in Y₂CaGe₄O₁₂:Er³⁺ is discussed for an 808 nm incident laser irradiation. A scheme of excitation and emission routes involving ground/excited state absorption, energy transfer upconversion, nonradiative multiphonon relaxation processes in trivalent lanthanide ions in Y₂CaGe₄O₁₂:Er³⁺ and Y₂CaGe₄O₁₂:Er³⁺, Yb³⁺ has been proposed. Conditions for visible emission occurrence under quasi-resonance λ_ex = 1064 nm excitation depending on pump power values are considered. In the low-power regime only near-infrared emission caused by the transition ⁴I_13/2 → ⁴I_15/2 in erbium ions has been detected.     

Preparation and characterization of Eu^3＋-doped CaCO3 phosphor by microwave synthesis

A Eu³⁺-doped CaCO₃ phosphor with red emission was prepared by microwave synthesis. The scanning electron microscopy (SEM) image and laser particle size analysis show that the CaCO₃:Eu³⁺ particles are needle-like in the length range of 5.0–10.0 μm. The results of X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FT-IR), and Raman spectroscopy indicate that pure aragonite CaCO₃:Eu³⁺ is prepared using microwave irradiation and the Eu³⁺ ion as a luminescence center inhabits the site of Ca²⁺. The photoluminescence excitation (PLE) spectrum shows that the strong broad band at around 270 nm and weak sharp lines in 300–550 nm are assigned to the charge transfer band of Eu³⁺-O²⁻ and intra-configurational 4f-4f transitions of Eu³⁺, respectively. The photoluminescence (PL) spectrum implies that the red luminescence can be attributed to the transitions from the ⁵D₀ excited level to the ⁷F _J (J = 0, 1, 2, 3, 4) levels of Eu³⁺ ions with the mainly electric dipole transition ⁵D₀ → ⁷F₂ (614 and 620 nm), and the Eu³⁺ ions prefer to occupy the low symmetric site in the crystal lattice.     

Enhancement of upconversion luminescence of Y2O3:Er nanocrystals by codoping Li-Zn

The upconversion (UC) luminescence in sol-gel synthesized Li⁺, Zn²⁺, or Li⁺-Zn²⁺ codoped Y₂O₃:Er³⁺ nanocrystals were investigated under the excitation of a 970 nm diode laser. Compared to undoped Y₂O₃:Er³⁺ samples, proper doping of Li⁺-Zn²⁺ leads to an drastic increase of the UC luminescence centered at 560 nm by a factor of 28. The UC luminescence enhancement is a result of the increased lifetime of the intermediate state ⁴I_11/2 (Er). The intensity ratio of the green over red emissions (green/red) is also affected by the codoping of Zn²⁺, Li⁺ and Li⁺-Zn²⁺ ions. Our results demonstrated that the Li⁺-Zn²⁺ codoping in Y₂O₃:Er³⁺ phosphors produced remarkable enhancement of the UC luminescence and green/red ratio, making this nanocrystal a promising candidate for photonic and biological applications.     

Structure and upconversion luminescence properties of BaYF5:Yb, Er nanoparticles prepared by different methods

BaYF₅:Yb³⁺, Er³⁺ (BYF) upconversion (UC) luminescence nanoparticles have been prepared using co-precipitation and hydrothermal techniques, respectively. Two different fluoride sources were used to synthesize BYF by the hydrothermal method, and the sizes of the as-prepared spherical particles were about 30 nm (NH₄BF₄ as a fluoride source) and 100 nm (NH₄HF₂ as a fluoride source), respectively. While the nanoparticles prepared by the co-precipitation method are irregular, many clusters and agglomerates can be seen. The UC fluorescence has been realized in all the as-prepared BYF samples upon 980 nm excitation. It is found that their luminescence spectra depend strongly upon the preparation method. Factors affecting the upconversion fluorescent intensity have been also studied. The UC emission transitions for ⁴F_9/2-⁴I_15/2 (red), ²H_11/2-⁴I_15/2 (green) and ⁴S_3/2-⁴I_15/2 (green) in the Yb³⁺/Er³⁺ codoped BYF nanoparticles depending on pumping power have also been discussed.     

Enhancement of the upconversion luminescence intensity in Er doped BaTiO3 nanocrystals by codoping with Li ions

Infrared-to-visible upconversion luminescence spectra were investigated in Er³⁺ doped and Er³⁺-Li⁺ codoped BaTiO₃ nanocrystals following excitation with 976 nm. By introducing Li⁺ ions, the upconverted emission intensity is found to be greatly enhanced compared to that of the nanocrystals without Li⁺ ions. The enhanced luminescence might be attributed to the oxygen vacancy generated by Li⁺ ion incorporation in the lattices and the distortion of the local asymmetry around Er³⁺. We observe that excitation power dependence and decay time are increased by the incorporation of Li⁺ ions. Li⁺ ions also can reduce the OH groups in specimen, which decrease nonradiative decay from the ⁴S_3/2 to ⁴F_9/2, enhancing the upconversion emission intensities.     

Effects of RE^3＋（RE=La,Ce,Pr,Sm,Dy,Ho,Er,and Tm） on the luminescence of Sr2MgSiO5：Eu^2＋ phosphors

Sr2MgSiO5:Eu2+phosphors were synthesized through a high temperature solid state reaction method.The phase and luminescence properties of the samples were characterized by X-ray diffraction(XRD) and a luminescence spectrometer.The effects of RE3+(RE = La,Ce,Pr,Sm,Dy,Ho,Er,and Tm) on the luminescent properties of the samples were studied.The results show that the luminescence spectrum of Sr2MgSiO5:Eu2+ is a broad band composed of two emission peaks,at 460 and at 530 nm under near-ultraviolet excitation.Rare earth ions Re3+(RE = La,Ce,Pr,Sm,Dy,Ho,Er,and Tm) have great influence on the emission of Sr2MgSiO5:Eu2+ phosphors.The La3+ ion in Sr2MgSiO5:Eu2+ phosphors greatly enhances the emission at 460 and 530 nm.     

Spectra and energy levels of Er3+ in Er2O3 powder

The emission and absorption spectra of Er³⁺ ions in Er₂O₃ powder are investigated at room temperature. The crystal field splitting of ⁴I_15/2, ⁴I_13/2, ⁴I_9/2 and ⁴S_3/2 multiplets of Er³⁺ was calculated using a parameterized Hamiltonian including crystal field terms. A final standard deviation of 5.3 cm⁻¹ is obtained between 22 calculated and experimental Stark. The strength crystal field parameters of Er₂O₃ powder are compared to those of erbium doped Y₂O₃ single crystal. In addition, the location of the ground and the first excited states of Er³⁺ in Er₂O₃ powder is determined. The ⁴I_15/2 ground state of Er³⁺ is located at 12750 cm⁻¹ below the valence band edge. The ⁴I_13/2 and ⁴I_11/2 multiplets are set in resonance with the valence band. A configuration coordinate diagram is proposed for Er³⁺ in Er₂O₃ powder.     

Phase Relations in the ZrO<Subscript>2</Subscript>-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>-Y<Subscript>2</Subscript>O<Subscript>3</Subscript> System: Experimental Study and Advanced Thermodynamic Modeling

Phase equilibria in the ZrO₂-Nd₂O₃-Y₂O₃ system at 1523-1873 K have been investigated by x-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive x-ray spectroscopy (SEM/EDX). Temperatures of phase transformations were determined by differential thermal analysis. Temperatures of invariant reactions in the ZrO₂-Nd₂O₃ system F = A + Pyr and H = F + A were determined as 1763 and 2118 K respectively and thermodynamic parameters of phases were re-assessed. Phase transformations in ternary systems were determined at 1732 K for composition ZrO₂-48.46Nd₂O₃-5.38Y₂O₃ (mol%) and at 1744 and 1881 K for composition ZrO₂-79.09Nd₂O₃-2.75Y₂O₃ (mol%). They were interpreted using XRD investigation before and after DTA as Pyr + B → F, Pyr → F and A → B, respectively. The solubility of the Y₂O₃ in pyrochlore phase was found to exceed 10 mol%. The thermodynamic parameters of the ZrO₂-Nd₂O₃-Y₂O₃ system were reassessed taking into account solubility of Y₂O₃ in the Nd₂Zr₂O₇ pyrochlore phase (Pyr). It is assumed that Y³⁺ substitutes Nd³⁺ and Zr⁴⁺ in their preferentially occupied sublattices. Ternary parameter was introduced into fluorite phase (F) for better reproducing of phase equilibria. Mixing parameters were reassessed for phase A (Nd₂O₃ based solution), monoclinic phase B and cubic phase C (Y₂O₃ based solution). The isothermal sections calculated for the ZrO₂-Nd₂O₃-Y₂O₃ system are in the reasonable agreement with experimental results.     

Sorption of Hg<Superscript>2+</Superscript>, Nd<Superscript>3+</Superscript>, Dy<Superscript>3+</Superscript>, and Uo<Stack><Subscript>2</Subscript><Superscript>2+</Superscript></Stack> ions at polysiloxane xerogels functionalized with phosphonic acid derivatives

The sorption properties of silicas with mono- and bifunctional surface layers containing the complexing fragment ≡Si(CH₂)₃NHP(S)(OC₂H₅)₂ were studied. It was found that xerogels synthesized by the solgel method (like mesoporous silicas obtained by the template method) can extract mercury(II) ions from acidified solutions (SSC up to 450 mg/g). In a nonporous xerogel with a bifunctional surface layer (≡P=S/-SH), thiol groups proved to be primary sorption sites for Hg²⁺ ions; part of the ligand groups were inaccessible to metal ions. Xerogels containing the phosphonic acid residues ≡Si(CH₂)₂P(O)(OH)₂ sorbed uranyl and lanthanide ions from their nitrate solutions. The resulting surface complexes contained two (for the UO ₂ ²⁺ ion) or three innersphere ligand groups (for the Nd³⁺ and Dy³⁺ ions). The maximum SSCs were 340 mg/g for the uranyl ion and 120 mg/g for the lanthanide ions.     

Polarized spectral analysis of Er ions in Er:LiGd(MoO4)2 crystal

The Er³⁺:LiGd(MoO₄)₂ crystal with Ø21 × 33 mm³ was grown by the Czochralski technique, and the absorption spectra, the fluorescence spectra and the fluorescence decay curves were measured at room temperature. Some spectroscopic parameters, such as the parameters of oscillator strengths, the spontaneous transition probabilities, the fluorescence branching ratios, the radiative lifetimes and the emission cross-sections were estimated based on Judd-Ofelt theory and Füchtbauer-Ladenburg method. The infrared emission at 1450-1650 nm, due to ⁴I_13/2 → ⁴I_15/2 transition and the visible emission at 520-569 nm corresponding to ²H_11/2,⁴S_3/2 → ⁴I_15/2 transition were observed in Er³⁺:LiGd(MoO₄)₂ crystals under 979 nm excitation at room temperature. The emission cross-sections are 4.37 × 10⁻²⁰ cm² at 553 nm and 0.584 × 10⁻²⁰ cm² at 1561 nm for π-polarization, and the following measured lifetimes are 4.57 ms and 10.74 μs. The upconversion emissions were attributed to energy transfer between Er³⁺ ions and the excited state absorption.     

Enhanced photoluminescence properties of CaYBO<Subscript>4</Subscript>:Tb<Superscript>3+</Superscript>,Al<Superscript>3+</Superscript> by doping Al<Superscript>3+</Superscript> for plasma display panel applications

The effect of photoluminescence properties for (CaY)_1−x−yTb_xAl_yBO₄ phosphors was studied, considering the doped Al³⁺ and Tb³⁺ contents. The emission intensity of the Al³⁺-doped (CaY)_0.915Tb_0.06Al_0.025BO₄ phosphors under VUV excitation was more than two times stronger than that of the Al³⁺-free (CaY)_0.94Tb_0.06BO₄. The contents of Tb³⁺ showing the strongest emission for the (CaY)_0.975−xTbxAl_0.025BO₄ and (CaY)_1−xTb_xBO₄ phosphors were x = 0.1 and 0.12, respectively. The results confirm that incorporating Al³⁺ in (CaY)_1−xTb_xBO₄ phosphors is highly favorable for improving emission characteristics, along with production cost-effectiveness.     

Effect of Bi doping on the quenching concentration of H11/2/S3/2 level of Er

Bi³⁺ and Er³⁺ codoped Y₂O₃ was prepared by sol-gel method. The upconversion emission was investigated under 980 nm excitation. For samples without Bi³⁺, the quenching concentration of ²H_11/2/⁴S_3/2 level of Er³⁺ is 3.0 mol%. However, by 1.5 mol% Bi³⁺ doping the quenching concentration increases to 5.0 mol%; meanwhile, the green emission is enhanced 1.9 times. The results indicate that both the quenching concentration and the emission intensity of ²H_11/2/⁴S_3/2 level can be increased by Bi³⁺ doping.     

Electrochemical behavior of zirconium in molten NaCl-KCl-K<Subscript>2</Subscript>ZrF<Subscript>6</Subscript> system

The electrochemical reduction of Zr4+(complex) ions in NaCl-KCl-K2ZrF6 molten salt on Pt electrode was investigated using cyclic voltammetry and square wave voltammetry at 1023 K.Two cathodic reduction peaks related to Zr4+/Zr2+ and Zr2+/Zr steps were observed in the cyclic voltammograms.The result was also confirmed by square wave voltammetry.The diffusion coefficient of Zr4+(complex) ions at 1023 K in NaCl-KCl-K2ZrF6 melt,measured by cyclic voltammetry,is about 4.22×10-6 cm2/s.The characterization of the deposits obtained by potentiostatic electrolysis at different potentials was investigated by XRD,and the results were well consistent with the electrochemical reduction mechanism of Zr4+(complex) ions.     

Phase Equilibria in the System Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO-CoO and Gibbs Energy of Formation of Ca<Subscript>3</Subscript>CoAl<Subscript>4</Subscript>O<Subscript>10</Subscript>

An isothermal section of the system Al₂O₃-CaO-CoO at 1500 K has been established by equilibrating 22 samples of different compositions at high temperature and phase identification by optical and scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy after quenching to room temperature. Only one quaternary oxide, Ca₃CoAl₄O₁₀, was identified inside the ternary triangle. Based on the phase relations, a solid-state electrochemical cell was designed to measure the Gibbs energy of formation of Ca₃CoAl₄O₁₀ in the temperature range from 1150 to 1500 K. Calcia-stabilized zirconia was used as the solid electrolyte and a mixture of Co + CoO as the reference electrode. The cell can be represented as: From the emf of the cell, the standard Gibbs energy change for the Ca₃CoAl₄O₁₀ formation reaction, CoO + 3/5CaAl₂O₄ + 1/5Ca₁₂Al₁₄O₃₃ → Ca₃CoAl₄O₁₀, is obtained as a function of temperature: /J mol⁻¹ (±50) = −2673 + 0.289 (T/K). The standard Gibbs energy of formation of Ca₃CoAl₄O₁₀ from its component binary oxides, Al₂O₃, CaO, and CoO is derived as a function of temperature. The standard entropy and enthalpy of formation of Ca₃CoAl₄O₁₀ at 298.15 K are evaluated. Chemical potential diagrams for the system Al₂O₃-CaO-CoO at 1500 K are presented based on the results of this study and auxiliary information from the literature.     

Phase Relations in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-MoO<Subscript>3</Subscript> System in the Solid State. The Crystal Structure of AlVO<Subscript>4</Subscript>

Phase relations in the ternary oxide system Al₂O₃-V₂O₅-MoO₃ in the solid state in air have been investigated by using the x-ray diffraction (XRD) and differential thermal analysis/thermogravimetric (DTA/TG) methods. It was confirmed that in the subsolidus area of the Al₂O₃-V₂O₅-MoO₃ system, there exist seven phases, that is Al₂O₃, V₂O_5(s.s.), MoO₃, AlVO₄, Al₂(MoO₄)₃, AlVMoO₇, and V₉Mo₆O₄₀. Seven fields, in which particular phases coexist at equilibrium, were isolated. The crystal structure of AlVO₄ has been refined from x-ray powder diffraction data. Its space group is triclinic, , Z = 6, with a = 0.65323(1) nm, b = 0.77498(2) nm, c = 0.91233(3) nm, α = 96.175(2)°, β = 107.234(3)°, γ = 101.404(3)°, V = 0.42555 nm³. The crystal structure of the compound is isotypic with FeVO₄. Infrared (IR) spectra of AlVO₄ and FeVO₄ are compared.     

Porous Y<Subscript>2</Subscript>O<Subscript>3</Subscript> microcubes: synthesis and characterization

In this work, a facile route using a simple solvothermal reaction and sequential heat treatment process to prepare porous Y₂O₃ microcubes is presented. The as-synthesized products were characterized by X-ray powder diffraction (XRD), scanning electronic microscope (SEM), energy dispersive spectrometer (EDS), thermogravimetric analysis (TG), and differential thermal analysis (DTA). The thermal decomposition process of the Y₂O₃ precursor was investigated. SEM results demonstrated that the as-prepared porous Y₂O₃ microcubes were with an average width of about 20 μm and thickness of about 8 μm. It was found that the morphology of the Y₂O₃ precursor could be readily tuned by varying the molar ratio of S₂O₈²⁻ to Y³⁺. Y₂O₃:Eu³⁺ (6.6%) microcubes were also prepared and their photoluminescence properties were investigated.