Photoluminescence properties and energy transfer in γ-irradiated Dy3+, Eu3+-codoped fluoroaluminoborate glasses

The photoluminescence (PL) properties of singly doped (Dy³⁺) and codoped (Dy³⁺, Eu³⁺) fluoroaluminoborate glasses, with an emphasis on the white light generation, are studied. The γ-irradiation led to the formation of defects in Dy³⁺-doped glasses and photoreduction of Eu³⁺ to Eu²⁺ in codoped (Dy³⁺, Eu³⁺) glasses. The electron paramagnetic resonance spectra confirm the presence of divalent europium ions and defects in Dy³⁺, Dy³⁺–Eu³⁺-doped glasses. The FTIR spectra mainly establish the compaction of glass network due to γ-irradiation. From the PL spectra, the intensity ratio of Dy³⁺ emission bands yellow to blue (⁴F_9/2–⁶H_13/2/⁴F_9/2–⁶H_15/2) defines the site symmetry, covalency, and feasibility of extracting white light. The existence of an energy transfer (ET) from Dy³⁺ to Eu³⁺ ions are established due to the decrease in intensity of Dy³⁺ peaks with an increase of Eu₂O₃ content. Moreover, the non-exponential nature of decay curves was well fitted with the generalization of Yokota–Tanimoto model for electric dipole-quadrupole (S = 8) interaction that is responsible for ET process from sensitizer (Dy³⁺) to activator (Eu³⁺).     

S-character of Cd+ centre in γ-irradiated alkali silicate glasses

The s-character of Cd⁺ centres and its fluctuation in -irradiated alkali silicate glasses were investigated using ESR spectroscopy. With increasing alkali content, the s-characters of Cd⁺ centres in sodium and potassium silicate glasses decrease monotonically whereas the s-character in lithium silicate glasses shows a maximum and then decreases. The temperature effect on compositional dependence of the s-character of a Cd⁺ centre is rarely observed in lithium silicate glasses. On the other hand, the temperature effect is clearly observed in sodium and it is suggested that local structures around Cd⁺ centres in sodium and potassium silicate glasses is relaxed by annealing at room temperature.     

Linear and nonlinear optical properties and luminescence of Dy+3-doped aluminoborate glasses: Judd–Ofelt investigation

The nominal glasses composition ((40-x) % H₃BO₃—30% CaO—30% Al₂O₃—x Dy₂O₃), where x?=?1, 2, 3, 4, 5 and 6) were prepared using the melt quenching technique. The absorption spectra reveal the common normal 13 transition peaks of the Dy₂O₃-doped glasses. The linear and nonlinear optical properties were calculated. The Photoluminescence spectra and the decay lifetime were examined. The Judd–Ofelt parameters trend was Ω₄?>?Ω₂?>?Ω₆. The oscillator strength of the experimental, and calculated electronic dipole absorption transition were estimated. The radiative life-time, the radiative branching ratio, the emission and absorption transition cross section were also calculated. The gain coefficient of the transitions was predicted. All the calculated parameters were compared with the previous work. The results reveal that the current glasses composition is a good candidate as a lasing host material and the glasses are highly efficient composition when using in the optical communication fibers.

     

Optical properties of Nd3+ and Er3+ ions in TeO2–WO3–PbO–La2O3 glasses

Multicomponent telluride-tungstate glasses containing Nd³⁺ and Er³⁺ ions were studied experimentally at 77 and 293 K using spectroscopic methods. The Judd–Ofelt intensity parameters were derived from the absorption spectra and used to calculate the radiative lifetimes and branching ratios. The quantum efficiency η = 0.95 of the ⁴F_3/2 level of Nd³⁺ ion is higher than the typical value of other tellurite-based glasses. For low concentration of Er³⁺ ions, the luminescence decay of the ⁴S_3/2 and ⁴I_11/2 levels is governed by radiative transitions and multiphonon relaxation involving the Te-O highest energy vibrations.     

Structural and luminescent properties of Er3+ and Tb3+-doped sol–gel-based bioactive glass powders and electrospun nanofibers

In this study, sol–gel-based erbium (Er³⁺), terbium (Tb³⁺) and Er³⁺: Tb³ co-doped 1393 bioactive glass powders and electrospun nanofibers were prepared. Structural and morphological properties of the bioactive glasses as well as the photoluminescence characteristics were investigated in detail. The median particle size and average diameter of the prepared glass powders and fibers were in the range of ~ 1.5–3.5 μm and 280–660 nm, respectively. The steady-state photoluminescence and decay kinetics of the samples were investigated under excitation (374 nm) where only Er³⁺ and Tb³⁺ ions close to Si nanoclusters can be excited. All the samples prepared in the study exhibited bright green emission upon excitation at 374 nm. Results showed that the dopant concentration and the sample morphology have significant influence on the photoluminescence and decay properties of the glasses. Sol–gel-derived bioactive glass particles exhibited stronger emission intensity, whereas electrospun nanofibers showed extended decay times. In vitro bioactivity experiments revealed that Er³⁺ and Tb³⁺ doping did not inhibit the conversion of the glass samples to hydroxyapatite treated in simulated body fluid for 30 days. It was concluded that Er³⁺ and Tb³⁺-containing 1393 bioactive glasses have a potential to be used in tissue engineering applications as well as bioimaging studies.

     

Optical absorption and photoluminescence properties of Eu3+-doped ZnF2–PbO–TeO2 glasses

Several physical, optical absorption and photoluminescence properties of Eu3+-doped ZnF2–PbO–TeO2 glasses have been studied. From the measured intensities of various absorption bands of these glasses the Judd–Ofelt parameters 2, 4 and 6 have been computed. The Judd–Ofelt theory has been applied to characterize the photoluminescence spectra of these glasses. From this theory, various radiative properties, such as transition probability, A, branching ratio, r, and emission cross-section, EP, for various emission levels of these glasses, have been determined and reported. © 1998 Chapman & Hall.     

Judd–Ofelt analysis and energy transfer processes of Er3+ and Nd3+ doped fluoroaluminate glasses with low phosphate content

Spectroscopic property and energy transfer processes of singly doped and codoped Er³⁺ and Nd³⁺ fluoroaluminate glasses with low phosphate content are systematically analyzed. The absorption spectra of these glasses are tested, and the Judd–Ofelt (J–O) and radiative parameters are discussed based on J–O theory and the parameters changes substantially because of the other codoping ions. As for Nd³⁺: the main emission bands at 0.9 and 1.05 μm decrease in the codoped sample under the excitation of an 800 nm laser diode from the emission spectra because the Er³⁺: ⁴I_11/2 level reduces the Nd³⁺: ⁴F_3/2 level effectively through the energy transfer process Nd³⁺: ⁴F_3/2 → Er³⁺: ⁴I_11/2. For Er³⁺, the emission at 1.5 μm is restrained by codoping with Nd³⁺ ions from the energy transfer process Er³⁺: ⁴I_13/2 → Nd³⁺: ⁴I_15/2. The emission at 2.7 μm is enhanced because the Nd³⁺ ions deplete the lower level and exert a positive effect on the upper laser level. The microparameters of the energy transfer between the Er³⁺ and Nd³⁺ ions are calculated and discussed using Forster–Dexter theory. The energy transfer efficiencies of the Nd³⁺: ⁴F_3/2 to the Er³⁺: ⁴I_11/2 and the Er³⁺: ⁴I_13/2 to the Nd³⁺: ⁴I_15/2 are 28.8% and 74.5%, respectively. These results indicate that Nd³⁺ can be an efficient sensitizer for Er³⁺ to obtain Mid-infrared (Mid-IR) emission and the codoped Er³⁺/Nd³⁺ fluoroaluminate glass with low phosphate content is suitable to be used as the fiber optical gain media for 2.7 μm laser generation.     

Photoluminescence and scintillation properties of Al(PO3)3–CsPO3–CsBr–CeBr3 glass scintillators

Scintillators, which are widely used as radiation detectors, are phosphors that release absorbed ionizing radiation energy as ultraviolet or visible light. Inorganic glass scintillators have several advantages over inorganic crystal scintillators, such as ease of fabrication and low costs. However, unlike inorganic crystals, which can emit up to tens of thousands of photons/MeV, inorganic glasses exhibit less than several hundred photons/MeV in most cases. Here, we studied an inorganic glass scintillator that exhibits a light yield of 2700 photons/MeV, which exceeds those of previous inorganic glass scintillators with high light yields of approximately 2000 photons/MeV. The density of this material is 3.28 g/cm³, which is relatively high among glass scintillators. Moreover, a fast scintillation decay with a decay time constant of 30.0 ns was obtained and is attributed to the 5d–4f transition of Ce³⁺. Thus, this glass is suitable for gamma- and X-ray detection, thereby expanding the practical applicability of inorganic glass scintillators.

     

Synthesis and Photoluminescence of Fluorinated Yttria–Alumina Composites

Inorganic Materials - Composites have been prepared via thermal decomposition of gel-like mixtures containing yttrium, aluminum, and europium(III) salts and ethyl acetate as a basic component....     

Microwave synthesis and properties of NaPO3–SnO–Nb2O5 glasses

Tin niobiophosphate glasses were produced using a domestic microwave oven under a nitrogen flow. The fast microwave melting method and the protective atmosphere prevent the oxidation of SnO. After 10 min of heating, the NaPO₃, SnO, and Nb₂O₅ mixtures are homogeneous and permit to obtain transparent glasses. Three series of glasses with different Sn/Nb ratio were studied to determine the influence of each oxide. The glass transition temperature increases linearly with the amount of Nb₂O₅ and SnO. These variations are more important for compositions with high metallic cation proportions and with a low Sn/Nb ratio. The same evolutions were observed for the density, Vickers hardness, and elastic modulus while the thermal expansion coefficient decreases monotonously. The simultaneous insertion of SnO and Nb₂O₅ in phosphate glass matrix leads to a progressive strengthening of the glass network. The chemical durability of the glasses also increases as a function of the amount of metal oxides. We prepared a bulk glass sample with a dissolution rate of about 3.3 × 10⁻⁸ g cm⁻² min⁻¹ in renewed water conditions at 95 °C. This durability is equivalent to those of the window glass whereas the glass transition temperature remains lower than 485 °C.     

Photoluminescence properties of Eu3+-activated CaMoO4 phosphors for WLEDs applications and its Judd–Ofelt analysis

A series of scheelite-type Eu³⁺-activated CaMoO₄ phosphors were synthesized by the nitrate–citrate gel combustion method. All the compounds crystallized in the tetragonal structure with space group I4 ₁ /a (No. 88). FESEM results reveal the spherical-like morphology. The CaMoO₄ phosphor exhibited broad emission centered at 500 nm under the excitation of 298 nm wavelength, while Eu³⁺-activated CaMoO₄ shows an intense characteristic red emission peak at 615 nm at different excitation wavelengths, due to ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. The intensities of transitions between different J levels depend on the symmetry of the local environment of Eu³⁺ ions and were estimated using the Judd–Ofelt analysis. The high asymmetric ratio revealed that Eu³⁺ occupies sites with a low symmetry and without an inversion center. The CIE chromaticity co-ordinates (x, y) were calculated from emission spectra, and the values were close to the NTSC standard. Therefore, the present phosphor is highly useful for LEDs applications.     

Spectroscopic properties of B2O3–PbO–Bi2O3–GeO2 glass doped with Sm3+ and gold nanoparticles

Heavy metal oxide B₂O₃–PbO–Bi₂O₃–GeO₂ transparent glass doped with Sm³⁺ was synthesized and implanted with Au⁺ using energy of 300 keV and fluence of 1 × 10¹⁶ cm⁻². The annealing of the implanted glass at moderate temperature below the glass transition temperature induced the nucleation of gold nanoparticles, confirmed by the characteristic absorption band in the visible range and by transmission electron microscopy. Using Miés and Doylés theories for the surface plasmon resonance, the average size of the gold nanoparticles was about 4.6 nm, similar to the values observed by transmission electron microscopy. It was also observed the crystallization of a thin layer of the glass at the implanted surface after annealing, detected by X-ray diffraction and scanning electron microscope. Visible and near-infrared emission of Sm³⁺ was enhanced after annealing of the glass implanted with gold. Judd–Ofelt parameters and radiative parameters were calculated for the glass doped with Sm³⁺ with and without gold nanoparticles.     

Luminescence and energy transfer in Er3+/Nd3+ ion-codoped Ge–In–S–CsBr chalcohalide glasses

This study investigates the emission properties of the Er³⁺/Nd³⁺ ions codoped 70GeS₂–10In₂S₃–20CsBr chalcohalide glasses. The vacuumed melt-quenching technique is employed to synthesize the glasses. The absorption spectra, upconversion and near-IR emission spectra as well as fluorescence decay curves are collected. With the increasing concentration of Er³⁺ ions, the lifetimes at 1073 nm for Nd³⁺ ions decrease from 538 to 420 μs under 808 nm excitation. Meanwhile, the lifetimes at 1540 nm for Er³⁺ ions decrease from 245 to 214 μs with the increasing concentration of Nd³⁺ ions. The emission spectra and lifetimes show that energy transfer exists between the Nd³⁺ and Er³⁺ ions. The luminescence and detailed energy transfer mechanisms are schematically proposed.     

Preparation and luminescence properties investigation of Eu3+, Tb3+-doped LaNbO4:RE3+ (RE = Eu,Eu/Tb,Tb)

Journal of Materials Science: Materials in Electronics - In this work, doped and co-doped LaNbO4:RE3+ (RE?=?Eu, Eu/Tb, Tb) single crystals were prepared by a unique hydrothermal method...     

Synthesis,structural and optical studies of sol–gel Gd2O3:Eu3+, Tb3+ films

Eu³⁺ and Tb³⁺ co-doped Gd₂O₃ films were elaborated by sol–gel process and dip-coating technique. The films were synthesized by hydrolysis of gadolinium pentanedionate. A homogeneous and stable sol was obtained by the reaction with acetylacetone. Gd₂O₃:Eu³⁺, Tb³⁺ films were crystallized around 500 °C; at an increase of temperature up to 700 °C, oriented growth of (4 0 0) face was observed. The obtained transparent Gd₂O₃: 2.5 at.% Eu³+, 0.005 at.% Tb³⁺ waveguide films at 700 °C display significant optical properties. Different crystallographic properties can be obtained in Gd₂O₃:Eu³⁺, Tb³⁺ films with varying sintering temperatures.     

Tb3+/Yb3+ codoped silica–hafnia glass and glass–ceramic waveguides to improve the efficiency of photovoltaic solar cells

In this paper we present the investigation of the energy transfer efficiency between Tb³⁺ and Yb³⁺ ions in silica–hafnia waveguides. Cooperative energy transfer between these two ions allows to cut one 488 nm photon in two 980 nm photons and could have important applications in improving the performance of photovoltaic solar cells. Previous works revealed that for a given concentration of donors (Tb³⁺), increasing the number of acceptors (Yb³⁺) located near to the Tb³⁺ ion can increase the Tb–Yb transfer probability. However, when increasing the density of active ions, some detrimental effects due to cross-relaxation mechanisms become relevant. On the basis of this observation the sample doping was chosen keeping constant the molar ratio [Yb]/[Tb] = 4 and the total rare earths contents were [Tb + Yb]/[Si + Hf] = 5%, 7%, 9%. The choice of the matrix is another crucial point to obtain an efficient down conversion processes with rare earth ions. To this respect a 70SiO₂–30HfO₂ waveguide composition was chosen. The comparison between the glass and the glass–ceramic structures demonstrated that the latter is more efficient since it combines the good optical properties of glasses with the optimal spectroscopic properties of crystals activated by luminescent species. A maximum transfer efficiency of 55% was found for the highest rare earth doping concentration.     

Preparation and optical properties of TPPS-doped metal–carboxylate-salts glasses

Li and Na carboxylate salts glasses with different number chains containing molecules of Tetraphenyl-porphine-tetrasulfonic acid (TPPS) were prepared by the melting method. TPPS doped in the glasses had the same form as the TPPS in the aqueous solutions. However the form of TPPS in the glasses changed because TPPS reacted with matrix glass during the melting process. Tetraphenyl-porphine (TPP) could no be incorporated into the Li and Na carboxylate salts glasses by the present melting method. The free base TPPS is important for photochemical hole burning (PHB) properties, and a mixed metal–carboxylate salts glasses containing free-base TPPS, which is the active form for PHB, were prepared by controlling the melting condition. It was found that a preparation condition such as holding time of the melts affects the formation of the complex of the TPPS and that in the mixed metal–carboxylate salts melts the TPPS formed a complex with Li but did not form a complex with Na.