Absorption and emission spectral studies of Sm-doped lead tungstate tellurite glasses

The present work reports the effect of concentration on photoluminescence properties of Sm³⁺ ions doped lead tungstate tellurite (LTTSm) glasses by using the absorption, emission and decay measurements. The Judd-Ofelt theory has been used to evaluate the three Judd-Ofelt intensity parameters (Ω_2,4,6) and calculated oscillator strengths (f_c). LTTSm glasses exhibited intense reddish-orange emission when excited with 477 nm wavelength. Concentration quenching has been noticed beyond 1.0 mol% of Sm³⁺ ion concentration. The decay curves of ⁴G_5/2 level exhibited single exponential behavior for all the concentrations and the measured lifetimes are found to depend strongly on Sm³⁺ concentration. From the emission characteristic parameters of ⁴G_5/2 level, it is concluded that the LTTSm glasses could be useful for photonic devices like visible lasers, fluorescent display devices and optical amplifiers.     

Preparation and its luminescent properties of AlPO4:Eu phosphor for w-LED applications

Orange-reddish-emitting phosphor AlPO₄:Eu³⁺ were fabricated by solid-state reactions at high temperature. X-ray diffraction analysis revealed that AlPO₄ doped with 3 mol% of Eu³⁺ (AlPO₄:0.03Eu³⁺) was pure orthorhombic phase. The photoluminescence study shows that the intensity of magnetic dipole transition (⁵D₀ → ⁷F₁) at 594 nm dominates over that of electric dipole transition (⁵D₀ → ⁷F₂) at 613 nm. The optimum concentration of Eu³⁺ for the highest luminescence is found to be 3 mol%. The PL excitation spectrum is composed of CTB of Eu-O and excitation lines of Eu³⁺ ions. The strongest excitation lines appeared at 392 nm. The color coordinates, quantum yield and lifetime for AlPO₄:0.03Eu³⁺ were measured. All the spectrum features indicate that AlPO₄:Eu³⁺ might be a promising phosphor for display devices or w-LEDs.     

Luminescence properties of bismuth-doped lime silicate glasses

Luminescences from bismuth-doped lime silicate glasses were investigated. Luminescences centered at about 400, 650, and 1300 nm were observed, excited at 280, 532 and 808 nm, respectively. These three luminescence bands arise from three different kinds of bismuth ions in the glasses. The visible luminescences centered at 400 and 650 nm arise from Bi³⁺, and Bi²⁺, respectively. The infrared luminescences cover the wavelength range from 1000 to 1600 nm when exited by an 808 nm laser diode. The full width at half maximum (FWHM) of the infrared luminescences is more than 205 nm. The intensity of the infrared luminescence decreases with the increment in CaO content. We suggest that the infrared luminescences might arise from Bi⁺. Such broadband luminescences indicate that the glasses may be potential candidate material for broadband fiber amplifiers and tunable lasers.     

Effect of Li2O on structure and optical properties of lithium bismosilicate glasses

Bismuth–silicate glasses containing lithium oxide having composition xLi₂O·(85 − x)Bi₂O₃·15SiO₂ (5 ≤ x ≤ 45 mol%) were prepared by melt quench technique. Density, molar volume and glass transition temperature for all the glass samples were measured. IR spectroscopy was used for structural studies of these glasses in the range from 400 to 1400 cm⁻¹. The increase of Li₂O content in glass matrix results in the decrease of the Si–O–Si bond angle and increase in the covalence nature of Bi–O bond. IR spectra suggest the presence of distorted [BiO₆] octahedral units and the degree of distortion increases with the addition of Li₂O in these glasses. The optical transmission spectra in the wavelength range from 200 to 3300 nm were recorded and optical band gap (E_g) was calculated. The values of E_g lie in between 2.81 and 2.98 eV. The values of average electronic oxide polarizability as well as optical basicity in these glasses were found to be dependent directly on Bi₂O₃/Li₂O ratio.     

Color-conversion and photoluminescence properties of Ba2MgW(Mo)O6:Eu phosphor

Compounds B₂AXO₆:Eu (B = Ba, Sr; A = Ca; and X = W, Mo) have recently been investigated and suggested to be color-conversion phosphor for WLED devices. In this work, we investigated the photoluminescence properties of the analogues Ba₂MgXO₆:Eu (X = W and Mo) and the energy transfer from W(Mo)O₆ groups to Eu³⁺ ions within the phosphors. The phase structure, UV-vis diffuse reflectance spectrum, photoluminescence properties and decay of Ba₂MgW_(1−x)Mo_xO₆:Eu were studied as a function of the W/Mo ratio. It was found that these phosphors showed excellent color-conversion capability from near-UV to orange-red light. The color-conversion process was considered to be performed by energy transferring from MoO₆ groups to doped Eu³⁺ ions. The MoO₆ → Eu³⁺ energy transfer efficiency could be greatly enhanced by partial substitution of Mo by W. The structure and photoluminescence properties of Ba₂AW_0.5Mo_0.5O₆:Eu (A = Ca and Mg, respectively) compounds were also investigated to reveal the effect of the Eu³⁺ ion coordination environment on its photoluminescence properties.     

Photoluminescence and time-resolved luminescence spectroscopy of novel NaBa4(BO3)3:Tb phosphor

This paper reports the photoluminescence (PL) properties of Tb³⁺ in NaBa₄(BO₃)₃, as well as the time-resolved luminescence properties. The PL excitation spectrum exhibits intense f → f transition absorption; the PL emission spectrum shows the strongest ⁵D₄ → ⁷F₅ emission at 540 nm. The relative intensity of ⁵D₃ emission is much weaker than that of ⁵D₄ emission even in the samples with lower Tb³⁺ concentration. The ⁵D₃ → ⁵D₄ cross-relaxation produces a marked increase in the ⁵D₃ decay rate with increasing Tb³⁺ concentrations and introduces a non-exponential component into the initial part of the decay. The dipole-dipole interaction is found to be responsible for the cross-relaxation. The decay curves of ⁵D₄ → ⁷F₅ transition exhibit an initial rise phenomenon. The two exponential fitting indicates that the initial slow rise is attributed to the ⁵D₃ → ⁵D₄ cross-relaxation process.     

One-step synthesis and properties of monolithic photoluminescent ruby colored cuprous oxide antimony oxide glass nanocomposites

Cuprous oxide (Cu₂O) antimony glass (K₂O-B₂O₃-Sb₂O₃) monolithic nanocomposites having brilliant yellow to ruby red color have been synthesized by a single-step melt-quench technique involving in situ thermochemical reduction of Cu²⁺ (CuO) by the reducing glass matrix without using any external reducing agent. The X-ray diffraction (XRD), infrared transmission and reflection spectra, and selected area electron diffraction analysis support the reduction of Cu²⁺ to Cu⁺ with the formation of Cu₂O nanoclusters along with Cu_ySb_2−x(O,OH)_6-7 (y ≤ 2, x ≤ 1) nanocrystalline phases while Cu⁰ nanoclusters are formed at very high Cu concentration. The UV-vis spectra of the yellow and orange colored nanocomposites show size-controlled band gap shift of the semiconductor (Cu₂O) nanocrystallites embedded in the glasses while the red nanocomposite exhibits surface plasmon resonance band at 529 nm due to metallic Cu. Transmission electron microscopic image advocates the formation of nanocystallites (5-42 nm). Photoluminescence emission studies show broad red emission band around 626 nm under various excitation wavelengths from 210 to 270 nm.     

Simultaneous tuning for excitation and emission of N doped Sr2SiO4:Eu for white light LEDs

Tunable color point and efficient excitation are two important challenges for improving white light LEDs. In this paper, red-shift in the emission spectra of Sr₂SiO₄:Eu has been achieved, and the excitation band has been tuned to fit the blue LED chips simultaneously by doping N into the host. XRD results showed that the unit cell volume markedly increased after nitridation. Moreover, nitridation resulted in the increase in weight loss, which can be attributed to the substitute of Si-O bonds by Si-N bonds. The effect of nitridation on the luminescence properties was well discussed.     

Optical properties of single doped Cr and co-doped Cr–Nd aluminum tantalum tellurite glasses

The optical properties for single doped Cr³⁺ and co-doped Cr³⁺–Nd³⁺ aluminum tantalum tellurite glasses have been studied as a function of temperature. For the single doped glass, the existence of two bands in the emission spectra at low temperature indicates the presence of two different sites for the Cr³⁺ ions, labelled as usual as low- and high-field sites. The broad band centred in the Near Infrared region, corresponds to low-field sites transition ⁴T₂→⁴A₂, and the narrow band centred at approximately 715 nm to the high-field sites transition ²E→⁴A₂. The emission intensity for both high- and low-field sites shows a strong decrease with increasing temperature, with the emission for the former sites vanishing at RT. In both cases the quenching observed with the increase of temperature can be ascribed to the presence of non-radiative relaxation mechanisms. Experimental observations for the co-doped glass show that both radiative and non-radiative energy transfer processes from Cr³⁺ to Nd³⁺ are present.     

Effect of ZrO2 addition on the microstructure and electromagnetic properties of YIG

In this work, we reported the microstructure and electromagnetic properties of a series of zirconium substituted yttrium iron garnet ferrites (YCaZrIG) with iron deficiency composition of Y_3−xCa_xZr_xFe_4.93−xO₁₂ (x = 0.1, 0.2, 0.3, and 0.4, with electrostatic balance by Ca²⁺ substituted for Y³⁺ ions) prepared by a solid-reaction method. The addition of ZrO₂ shows no obvious influence on the phase, density and dielectric constant of YIG ferrites. When Zr addition x ≤ 0.3, the substitution of Zr⁴⁺ for Fe³⁺ decreases the amount of Fe ions, increases the lattice parameter and enhances the grain growth of garnet phase. The solubility of zirconium in YCaZrIG ferrite was found to be approximately 0.3, above which excess ZrO₂ would lead to the precipitation of a second phase inside the YCaZrIG ferrite. This would inhibit the grain growth of garnet phase and cause an increase in the dielectric loss and coercivity. The observed reduce for saturation magnetization when x = 0.4 is possibly due to antiparallel alignment of magnetic moment of Fe³⁺ in the d site caused by the decrease of a-d exchange interaction. Additionally, we got the optimum electromagnetic properties in the samples with x = 0.3: ?_r = 14.1, tan δ_e = 2.5 × 10⁻⁴, H_c = 47 A/m, 4πM_s = 1936 × 10⁻⁴T, ΔH = 7.1 KA/m.     

Enhanced photoluminescence of BaMgAl10O17:Eu nanophosphor for PDP application

BaMgAl₁₀O₁₇:Eu²⁺ nanorods were synthesized by sol-gel technique, and their luminescent properties were investigated upon the irradiation of vacuum ultraviolet (VUV) light. By introducing surfactant cetyl-tri-methyl-ammonium bromide (CTAB) in sol-gel process and additional Mg²⁺ in the raw materials, the emission intensity and thermal stability of the nanophosphor were both enhanced. The above improvements made it possible that the nanosized BAM phosphor could be a good alternative for PDP application.     

Effects of Bi doping on the optical properties of Er:Y2O3

The influences of Bi³⁺ doping on the optical properties of Er³⁺:Y₂O₃ are investigated under UV and IR excitations. The emission intensity of Er³⁺ is remarkably enhanced by the introduction of Bi³⁺ under both two excitations. The emission enhancement under UV excitation originates from the energy transfer from Bi³⁺ to Er³⁺, while under IR excitation it can be attributed to the modification of the local crystal field around the Er³⁺.     

Synthesis, crystal and band structures, and optical properties of a new framework mercury pnictides: [Hg4As2](InBr3.5As0.5) with tridymite topology

A new framework compound, [Hg₄As₂](InBr_3.5As_0.5) (1), has been prepared by the solid-state reaction of Hg₂Br₂ with elemental In and As at 450 °C. Compound 1 crystallizes in the space group P₆₃/mmc of the Hexagonal system with two formula units in a cell: a = b = 7.7408(6) Å, c = 12.5350(19) Å, V = 650.47(12) Å³. The crystal structure of 1 features a novel 3D framework, [Hg₄As₂]²⁺ with tridymite topology. The optical properties were investigated in terms of the diffuse reflectance and infrared spectra. The electronic band structure along with density of states (DOS) calculated by DFT method indicates that the present compound is semiconductor, and the optical absorption is mainly originated from the charge transitions from Br-4p and As-4p states to Hg-6s and In-5p states.     

Improvement of optical properties of nanocrystalline Fe-doped ZnO powders through precipitation method from citrate-modified zinc nitrate solution

Nanocrystalline Zn_1−xFe_xO (where x = 0, 0.01 and 0.02) powders were successfully synthesized by a precipitation method from citrate-modified zinc nitrate solution. X-ray powder diffraction, Fourier transformed infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy were used to study the structural properties. The optical properties were determined by UV–vis spectrophotometer and luminescent spectrometer. In this study, the optical band gap of nanocrystalline ZnO powder increased from 3.170 eV to 3.214 eV when the Fe concentration in the solution was increased up to 2 mol. %.     

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.     

Influence of niobium doping on phase composition and defect-mediated photoluminescence properties of Eu-doped TiO2 nanopowders synthesized in Ar/O2 thermal plasma

Nb⁵⁺:Eu³⁺-codoped TiO₂ nanopowders for chemical composition adjustment have been synthesized via Ar/O₂ radio-frequency thermal plasma. X-ray diffraction (XRD) results reveal that all the resultant powders exhibited mixture polymorphs of anatase (mean size: ∼45 nm) as the major phase and rutile (mean size: ∼71 nm). Rutile formation was promoted by the Eu³⁺ doping but suppressed by the Nb⁵⁺ addition. Combined observation using FE-SEM and TEM indicates that all the plasma-synthesized powders had a majority of facet-shaped particles (several nanometers) and a small proportion of nearly spherical crystals (∼150 nm). For the defect-mediated photoluminescence (PL) emission through the energy transfer from the TiO₂ host to the Eu³⁺ activator, the PL intensity originating from the ⁵D₀ → ⁷F₂ electronic transition weakened but that from the ⁵D₀ → ⁷F₁ electronic transition strengthened with increasing Nb⁵⁺ content. This may be a result of the decrease in the oxygen vacancy defects in the TiO₂ host lattice, as revealed by the joint means of UV-vis absorption spectra and excitation and emission spectra.     

High yield luminescence of a novel europium complex by excimer excitation and f–f absorption of Eu

A new organic ligand, 2-allyl-1,3-diphenyl-1,3-propanedione (ADP), and the corresponding quaternary Eu³⁺ complex, bi (ADP) (dibenzoyl methane) (1,10-phenanthroline) europium(III) [Eu(ADP)₂(DBM)(Phen)] have been synthesized. Excellent red luminescence from the Eu³⁺ complex was observed excited at 419 nm, and the broad visible excitation band is attributed to excimer absorption. The luminescence quantum yield excited at 419 nm (34 ± 3%) was higher than that at 380 nm (30 ± 3%). This is the first time to find strong and high yield excimer excitation absorption for a europium complex at room temperature, therefore, the excimer absorption band located in visible region (400–500 nm). Moreover, very high yields of direct f–f excitation absorption of Eu³⁺ ions at 466 nm (104 ± 10%) and 536 nm (96 ± 10%) were firstly observed, and the excitation spectrum for the europium complex in solid state is extended in wide region from 220 nm to 580 nm.     

Formation and properties of the Zr75−xAlxNi10Cu10Ti5 bulk metallic glasses

Zr-based bulk metallic glasses (BMGs) exhibit interesting mechanical properties since they combine high fracture stress, elastic strain (up to 2%), significant fracture toughness and good corrosion resistance. Quaternary systems with general composition Zr–Ni–Cu–Ti show wide composition ranges in which BMG can be obtained. The addition of the another element to the quaternary alloys often increases the glass forming ability (GFA). The aim of this work was to study the influence of aluminium content on the GFA and on the mechanical properties of the Zr–Ni–Cu–Ti alloys. Multicomponent Zr_75−xAl_xNi₁₀Cu₁₀Ti₅ (x = 15, 20 at%) alloys were produced by melt spinning method obtaining ribbons, and by casting technique into a copper mould, manufacturing rod shape samples with maximum diameter of 2 mm. Supercooled liquid region depends on chemical composition and exceeds 45 °C. Vickers microhardness of studied alloys is comparable to the highest ones for other Zr-based BMG.