Luminous properties of skin–core structure new luminous fiber: SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>,Dy<Superscript>3+</Superscript>-PET/light conversion agent-PET

SrAl₂O₄:Eu²⁺,Dy³⁺-polyethylene terephthalate (PET)/light conversion agent-PET, which is a new skin–core structure luminous fiber that can emit red light in the darkness, was fabricated by melt spinning with the combination of light conversion agent-PET and SrAl₂O₄:Eu²⁺,Dy³⁺-PET. An energy transfer occurred between SrAl₂O₄:Eu²⁺,Dy³⁺ and light conversion agent, and the light conversion agent emitted red light absorbed from SrAl₂O₄:Eu²⁺,Dy³⁺. To investigate the effect of light conversion agent on the luminous properties of SrAl₂O₄:Eu²⁺,Dy³⁺-PET-light conversion agent, several kinds of luminous fiber that contained different light conversion agents were artificially manufactured and their luminous properties were investigated. Results showed that under near-ultraviolet excitation, the fluorescent color of luminous fiber was primarily located in the orange-red area, with more intense red color than the others.     

Intense 2.0 µm emission from Ho<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> co-doped Na<Subscript>5</Subscript>Lu<Subscript>9</Subscript>F<Subscript>32</Subscript> single crystal excited by 980 nm

This paper reported on optical spectra of Na₅Lu₉F₃₂ single crystals co-doped with ~?0.91 mol% Ho³⁺ and various Yb³⁺ concentrations by using an improved Bridgman method. The emission spectra and fluorescence decay curves were measured to investigate the luminescent properties of the Ho³⁺/Yb³⁺ co-doped Na₅Lu₉F₃₂ and the energy transfer process from Yb³⁺ to Ho³⁺ ion. Compared with the Ho³⁺ singly doped Na₅Lu₉F₃₂ crystal, the Ho³⁺/Yb³⁺ co-doped crystal had an obviously enhanced emission at 2.0 µm via the 980 nm laser diode excitation because of the efficient energy transfer from Yb³⁺ to Ho³⁺ ion. The maximum emission intensity at 2.0 µm was obtained at about 6.99 mol% Yb³⁺ concentration when the concentration of Ho³⁺ ions is fixed at ~?0.91 mol% in the current research. The maximum emission cross section of the above sample at 2.0 µm was calculated to be 1.23?×?10^?20 cm² according to the measured emission spectrum. The energy transfer efficiency from Yb³⁺:²F_5/2 to Ho³⁺:⁵I₆ for the crystal was estimated up to 90.8% indicating that Yb³⁺ ions can efficiently sensitize the Ho³⁺ ions.     

Luminescent properties of single-phase Ba<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>:Tb<Superscript>3+</Superscript>, R (R = Eu<Superscript>2+</Superscript>, Ce<Superscript>3+</Superscript>) phosphors for white LED

The Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) phosphors were synthesized by use of a co-precipitation method. Crystal phase, excitation and emission spectra of sample phosphors are analyzed by means of XRD and FL, respectively. The emission spectra of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors exhibit four linear peaks attributed to the ⁵D₄?→?⁷F_J (J?=?6–3) transition of Tb³⁺ while four broad emission bands are observed in the emission spectra of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The effects of Eu²⁺ concentration on the luminescent properties of Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) are studied. Ce³⁺ affects the luminescent properties of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors just as the sensitizer. However, Eu²⁺ is considered both as the sensitizer and the activator in Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The chromaticity coordinates of Eu²⁺ and Tb³⁺ co-doped phosphors gather around the white light field with the CCT approximate to 5000 K, indicating that the luminescent property of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors may approach to a desired level needed for white LED application.     

Near-infrared downconversion in Ce<Superscript>3+</Superscript>–Yb<Superscript>3+</Superscript> co-doped YAG

The phosphors YAG co-doped with Ce³⁺–Yb³⁺ ion pair were successfully synthesized by solid state reaction method varying the concentration of Yb³⁺ ions from 1 to 15 % mol. The phosphors were characterized by powder X-ray powder diffraction and surface morphology was studied by scanning electronic microscope. The photoluminescence (PL) properties were studied by spectrophotometers in near infra red (NIR) and ultra violet visible region. The synthesized phosphors can convert a photon of blue region (469 nm) into photons of NIR region (979 and 992 nm). The co-operative energy transfer was studied by time decay curve and PL spectra. The theoretical value of quantum efficiency was calculated from steady time decay measurement and the maximum efficiency approached up to 145.19 %. Hence this phosphor could be used as a downconversion luminescent convertor in front of crystalline silicon solar cell (c-Si) panels to reduce thermalization loss due to spectral mismatch of the solar cells.     

Synthesis and luminescent properties of Sr<Subscript>4</Subscript>Al<Subscript>14</Subscript>O<Subscript>25</Subscript>:Eu<Superscript>2+</Superscript> blue–green emitting phosphor for white light-emitting diodes (LEDs)

An efficient blue–green emitting phosphor, Sr₄Al₁₄O₂₅:Eu²⁺, was prepared by solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the formation of Sr₄Al₁₄O₂₅:Eu²⁺. Field-emission scanning electron-microscopy (FE-SEM) observation indicated that the microstructure of the phosphor consisted of irregular fine grains with an average size of about 8–10 μm. Photoluminescence measurements showed a broad absorption band between 300 and 450 nm which was efficiently excited by near-ultraviolet (NUV) LEDs (350–410 nm) and a strong emission band peaking at 491 nm. A bright blue–green LED with chromatic coordination (0.176, 0.412) was fabricated by incorporating the phosphor with an InGaN-based NUV chip, which indicates that Sr₄Al₁₄O₂₅:Eu²⁺ is a good candidate phosphor for application in white LEDs.     

Photoluminescence,Judd–Ofelt analysis and photometric characterization of Eu<Superscript>3+</Superscript> activated Ca<Subscript>0.5</Subscript>Gd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> red phosphor

The red emitting Ca_0.5Gd(WO₄)₂:Eu³⁺ was synthesized by a solid-state reaction method. X-ray diffraction patterns were used to characterize crystal structure as well as phase purity. The results suggest that the as synthesized powder phosphor possess scheelite crystal structure with tetragonal symmetry along with the space group of I4₁/a. SEM studies reveal that the as synthesized sample show polyhedral morphology with particle size of 5.5 µm. Photoluminescence excitation spectrum depicts that a broad band (from 200 to 300 nm) centered at 242 nm is attributed to the ligand to metal charge transfer transition of WO₄ ^2? and three intense with sharp absorption bands (observed at 394, 464 and 535 nm) are designated as f–f electronic transitions of Eu³⁺. Photoluminescence emission studies indicate that, under 394 nm UV excitation, a hypersensitive red emission was observed at 617 nm due to the transition from upper ⁵D₀ level to the ⁷F₂ lower level of Eu³⁺ ion. The spectroscopic behaviour of the as synthesized phosphor Ca_0.5Gd(WO₄)₂:Eu³⁺ was determined using Judd–Ofelt theory. The CIE color coordinates, colour correlated temperature and luminous efficacies of radiation were estimated. The as obtained results indicating that the Ca_0.5Gd(WO₄)₂:Eu³⁺ red phosphor is most suitable for solid state lighting applications.     

Ln<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Mn<Superscript>4+</Superscript> (Ln = Y and Lu): non-rare-earth doped red phosphor for improving light properties of white light emitting diodes

We fabricated a series of Y₃Al₅O₁₂:Mn⁴⁺ and Y_1?yLu_yAl₅O₁₂:Mn⁴⁺ phosphors by a solid state reaction. The phase and the optical properties of the synthesized phosphors were investigated. Under the excitation at 465 nm, Y₃Al₅O₁₂:Mn⁴⁺ phosphors show emission bands locating at deep red regions, which is induced by the spin- and parity-forbidden ²E_g → ⁴A_1g transitions of Mn⁴⁺. The substitution of Y³⁺ by Lu³⁺ decreases the lattice parameter and thus strengthens the crystal field strength, which gives rise to the blue shift of emission band for Y_1?yLu_yAl₅O₁₂:Mn⁴⁺ phosphors. Due to the compensation of red light by Y₃Al₅O₁₂:Mn⁴⁺ or Y_1?yLu_yAl₅O₁₂:Mn⁴⁺ phosphor, the values of correlated-color-temperature for fabricated LEDs are decreased, which leads to the suitable application for them in indoor illumination.     

Structure,electrical, and optical properties of ZnO-substituted PbO for the Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> co-doped Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–GeO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O glass system

Glasses of the 0.5Er³⁺/2.5Yb³⁺ co-doped (40Bi₂O₃–20GeO₂–(30 − x)PbO–xZnO–10Na₂O system where x = 0.0, 5, 10, 15, 20, 25, and 30 mol%) have been characterized by FT-IR spectroscopy measurements to obtain information about the influence of ZnO-substituted PbO on the local structure of the glass matrix. The density and the molar volume have been determined. The influences of the ZnO-substituted PbO on the structure of glasses have been discussed. The dc conductivity measured in the temperature range 475–700 K obeys Arrhenius law. The conductivity decreases while the activation energy for conduction increases with increase ZnO content. The optical transmittance and reflectance spectrum of the glasses have been recorded in the wavelength range 400–1100 nm. The values of the optical band gap E _opt for all types of electronic transitions and refractive index have been determined and discussed. The real and imaginary parts ε₁ and ε₂ of dielectric constant have been determined.     

Photoluminescence of Eu<Superscript>3+</Superscript> ion in SnO<Subscript>2</Subscript> obtained by sol–gel

Photoluminescence data of Eu-doped SnO₂ xerogels are presented, yielding information on the symmetry of Eu³⁺ luminescent centers, which can be related to their location in the matrix: at lattice sites, substituting to Sn⁴⁺, or segregated at particles surface. Influence of doping concentration and/or particle size on the photoluminescence spectra obtained by energy transfer from the matrix to Eu³⁺ sites is investigated. Results show that a better efficiency in the energy transfer processes is obtained for high symmetry Eu³⁺ sites and low doping levels. Emission intensity from ⁵D₀→⁷F₁ transition increases as the temperature is raised from 10 to 240 K, under excitation at 266 nm laser line, because in this transition the multiphonon emission becomes significant only above 240 K. As an extension of this result, we predict high effectiveness for room temperature operation of Eu-based optical communication devices. X-ray diffraction data show that the impurity excess inhibits particle growth, which may influence the asymmetry ratio of luminescence spectra.     

Cathodoluminescence properties of SiO<Subscript>2</Subscript>:Pr<Superscript>3+</Superscript>and ZnO·SiO<Subscript>2</Subscript>:Pr<Superscript>3+</Superscript> phosphor nanopowders

The successful incorporation of ZnO nanoparticles in Pr³⁺-doped SiO₂ using a sol–gel process is reported. SiO₂:Pr³⁺ gels, with or without ZnO nanoparticles, were dried at room temperature and annealed at 600 °C. On the basis of the X-ray Diffraction (XRD) results, the SiO₂ was amorphous regardless of the incorporation of Pr³⁺ and nanocrystalline ZnO or annealing at 600 °C. The particles were mostly spherical and agglomerated as confirmed by Field Emission Scanning Electron Microscopy. Thermogravimetric analysis of dried gels performed in an N₂ atmosphere indicated that stable phases were formed at ≥900 °C. Absorption bands ascribed to ³H₄-³P_{(J = 0,1,2)}, ¹I₆ and ¹D₂ in the UV–VIS region were observed from SiO₂:Pr³⁺ colloids. The red cathodoluminescent (CL) emission corresponding to the ³P₀ → ³H₆ transition of Pr³⁺ was observed at 614 nm from dried and annealed SiO₂:Pr³⁺ powder samples. This emission was increased considerably when ZnO nanoparticles were incorporated. The CL intensity was measured at an accelerating voltage of 1-5 keV and a fixed beam current of 8.5 μA. The effects of accelerating voltage on the CL intensity and the CL degradation of SiO₂:Pr³⁺ and ZnO·SiO₂:Pr³⁺ were also investigated using Auger electron spectroscopy coupled with an Ocean Optics S2000 spectrometer.     

Y<Subscript>2</Subscript>O<Subscript>2</Subscript>S:Er<Superscript>3+</Superscript>,Ce<Superscript>3+</Superscript>—A new “invisible” IR phosphor

Ce³⁺ doping of Y₂O₂S:Er³⁺ can be used to suppress the visible anti-Stokes luminescence of the phosphor under excitation in the range 0.90–0.98 μm. We take advantage of this effect to create a new, efficient “invisible” IR phosphor emitting in the range 1.5–1.6 μm.     

Cost-effective electrostatic-sprayed SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2 + </Superscript> phosphor coatings by using salted sol–gel derived solution

3 Mol% of europium doped strontium aluminate (SrAl₂O₄:Eu^2 +) coatings on silicon substrates were prepared by electrostatic spray deposition method using a salted sol–gel derived solution as a starting material. As-deposited films at 100°C for 5 h were heated at 1100°C for 2 h under a reducing ambient atmosphere of 95%N₂ + 5%H₂. Nanocrystalline SrAl₂O₄ film was confirmed by surface morphological and crystallographic analyses. Monitored at 520 nm, the excitation spectrum showed a broad band from 300 ~ 500 nm and the emission intensity showed a maximum yellow peak intensity at 512 nm with a broad band from 460 ~ 610 nm.     

Tunable luminescence of Sr<Subscript>5(1−x)</Subscript>Ba<Subscript>5x</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>Cl:Eu<Superscript>2+</Superscript> (0 ≤ x ≤ 100%) phosphors from different Eu<Superscript>2+</Superscript> centers

In this paper, a series of Eu²⁺ activated Sr_5(1?x)Ba_5x(PO₄)₃Cl (0?≤?x?≤?100%) phosphors were prepared by solid-state reaction method, and their luminescence properties under near-ultraviolet excitation were investigated. For Eu²⁺-activated Sr₅(PO₄)₃Cl, a strong emission band located at 445 nm is observed upon 365 nm excitation, which could be attributed to the 4f ⁶5d ¹–4f ⁷ transition of different Eu²⁺ centers. When the Ba²⁺ is introduced into the Sr₅(PO₄)₃Cl:Eu²⁺, the emission band of Eu²⁺ is broadened largely. The fluorescence lifetimes for different Eu²⁺ centers were determined by the decay curves and time-resolved spectra. The excitation spectra of the as-prepared samples cover a wide wavelength range from 240 to 420 nm, which can well match the emission wavelength of the near ultraviolet LED chip. The investigation of the thermal luminescence stability reveals that the introduction of Ba²⁺ could improve the thermal quenching properties.     

Synthesis of Yb<Superscript>3+</Superscript>, Ho<Superscript>3+</Superscript> and Tm<Superscript>3+</Superscript> co-doped β-NaYF<Subscript>4</Subscript> nanoparticles by sol–gel method and the multi-color upconversion luminescence properties

Well-crystalline β-NaYF₄:Yb³⁺, Ho³⁺, Tm³⁺ nanoparticles were synthesized by sol–gel method using isopropyl alcohol [(CH₃)₂CHOH] as a complexing agent. The samples were characterized by X-ray diffraction, scanning electron microscopic analysis and fluorescence spectrum analysis methods. Under the excitation of 980 nm laser diode (LD), the samples displayed bright upconversion luminescence (UCL), which was generated from the energy level transition of Ho³⁺ and Tm³⁺ ions. With the increase of Tm³⁺, Ho³⁺ and Yb³⁺-doping concentration, the UCL intensity of blue, green and red light emission of the samples varied. Calculation of the CIE color coordinate of the β-NaYF₄:Yb³⁺, Ho³⁺, Tm³⁺ nanoparticles revealed that with the adjustment of Tm³⁺, Ho³⁺ and Yb³⁺ doping concentration and the excitation power of 980 nm LD, the multi-color UCL can be realized. Approximately single red light output with the CIE color coordinate of x?=?0.545, y?=?0.306 and white light output with the CIE color coordinate of x?=?0.325, y?=?0.320 can be obtained in the synthesized β-NaYF₄: Yb³⁺, Ho³⁺, Tm³⁺ nanoparticles.     

Synthesis of Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Ce<Superscript>3+</Superscript> phosphor in the Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al metal–CeO<Subscript>2</Subscript> ternary system

Garnet phosphor Y₃Al₅O₁₂:Ce³⁺ is prepared in the Y₂O₃–Al metal–CeO₂ ternary system by the solid-state reaction method in the air. For the first time, metal Al is used as a source of aluminum for the reaction instead of traditional oxide Al₂O₃. It is shown that the chemical reaction can be realized at lower temperatures and without use of special reducing atmosphere. The structural and spectroscopic properties of the prepared powder phosphor are very close to those earlier reported for the Y₃Al₅O₁₂:Ce³⁺ single crystal.     

Optical properties of Dy<Superscript>3+</Superscript>-doped sodium–aluminum–phosphate glasses

Trivalent dysprosium (Dy³⁺)-doped sodium–aluminum–phosphate (NAP) glasses were prepared and characterized by their optical absorption, excitation, emission spectra, and decay time measurements. Judd–Ofelt intensity parameters were derived from the absorption spectrum and used to calculate the radiative lifetime and stimulated emission cross section of the ⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → ⁶H_15/2 transitions. The luminescence intensity ratio of ⁴F_9/2 → ⁶H_13/2 to ⁴F_9/2 → ⁶H_15/2 transitions of Dy³⁺ in NAP glasses gives the feasibility of extracting white light. The lifetime and quantum efficiency of ⁴F_9/2 level is found to be higher than other reported glasses. With increase in Dy³⁺ ion concentration, the decay from ⁴F_9/2 level is found to be faster with decrease in lifetime due to cross relaxation between Dy³⁺ ions.     

Ho<Superscript>3+</Superscript>-Doped ZrF<Subscript>4</Subscript>–BaF<Subscript>2</Subscript>–BiF<Subscript>3</Subscript> Ceramic 2-µm laser beam visualizer

A ceramic 2-µm laser beam visualizer based on Ho³⁺-doped β-BaZrF₆ is proposed. The ceramic has been prepared by crystallizing 60ZrF₄–35BaF₂–5BiF₃ glass doped with 3 wt % HoF₃. Exciting the Ho³⁺⁵I₇ level by a Tm:LiYF₄ (Tm:YLF) laser at λ = 1910 nm, we observed a strong red luminescence, due to the ⁵F₅ → ⁵I₈ transition, and a weaker, green luminescence, corresponding to the (⁵F₄, ⁵S₂) → ⁵I₈ transition. The threshold power density of the Tm:YLF laser at which a red spot was observed on a ceramic sample was 1.1 W/cm².     

Visible quantum cutting in Tb<Superscript>3+</Superscript> doped BaGdF<Subscript>5</Subscript> phosphor for plasma display panel

Visible quantum cutting (QC) via down-conversion and enhancement in photoluminescence properties has been observed in terbium (Tb³⁺) doped BaGdF₅ phosphor. This phosphor was synthesized by varying molar concentration of Tb³⁺ ions via co-precipitation method. The prepared phosphor was characterized through X-ray diffraction technique. The photoluminescence spectra of BaGdF₅:Tb³⁺ phosphor measured under vacuum ultraviolet or UV excitation. The QC process was observed in prepared phosphor due to cross relaxation and direct energy transfer between Tb³⁺ and Tb³⁺ or Tb³⁺ and Gd³⁺ ions depending on the excitation wavelength. The maximum quantum efficiencies were found to be 162, 174 and 177 %, under the excitation of 172, 187 and 240 nm respectively. The green emission of 544 nm was observed at excitation of 172 and 187 nm. Hence this phosphor may be prime candidate for application in plasma display panels and mercury free fluorescent lamps.     

Structural and electrical properties of Ho<Superscript>3+</Superscript>-modified Pb(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>–9PbTiO<Subscript>3</Subscript> single crystals

Ho³⁺-modified Pb(Zn_1/3Nb_2/3)O₃–9PbTiO₃ (PZN–9PT) single crystals were grown through a flux method. Phase structure and microstructural morphology of the as-grown single crystals were performed by X-ray diffraction analysis and scanning electron microscopy. The refinement of the lattice parameters were obtained by the Rietveld method. The electrical properties of PZN–9PT single crystals were improved significantly by the modification of Ho³⁺ ions. The rhombohedral–tetragonal phase transition temperature, Curie temperature, coercive field at 15 kV cm^?1, and remnant polarization of Ho³⁺-modified PZN–9PT single crystals were increased by 14, 42 K, 2.4 kV cm^?1, and 7.5 μC cm^?2, respectively (i.e., 375.45, 448.45 K, 5.9 kV cm^?1, and 38.40 μC cm^?2, respectively). Furthermore, Lorentz-type law was used to describe the dielectric relaxor behavior of the as-grown single crystals.     

Spectroscopic properties of Nd<Superscript>3+</Superscript>, Yb<Superscript>3+</Superscript>-doped and Nd<Superscript>3+</Superscript>–Yb<Superscript>3+</Superscript>-codoped high silica glass

The Nd³⁺, Yb³⁺-doped and Nd³⁺–Yb³⁺-codoped high silica glasses (HSGs) were fabricated by sintering porous glasses impregnated with Nd³⁺ and Yb³⁺ ions solutions. The Judd–Ofelt theory was used to study the spectroscopic properties of Nd³⁺-doped HSGs. Large parameter Ω₂ of Nd³⁺-doped HSGs suggests a lower centrosymmetric coordination environment around the Nd³⁺ in HSG. The spontaneous emission probability and emission cross-section (σ_em) of Yb³⁺-doped HSGs are obtained. A broad emission band from 950 to 1,100 nm was detected when the Nd³⁺–Yb³⁺-codoped HSG was excited by 808 nm LD. The energy transfer process from Nd³⁺ to Yb³⁺ in HSG was described in this paper.