Time-resolved fluorescence measurements on Dy3+ and Sm3+ doped glasses

Various fluoride, phosphate and borosilicate glasses with known properties and global structure have been doped with Dy³⁺ (4f⁹) and Sm³⁺ (4f⁵) between 10¹⁸ and 10²¹ cm^?3 and their time resolved fluorescence in the visible range in combination with characteristic physical properties were studied. Different fit procedures were carried out. Although both ions differ in their intrinsic fluorescence lifetime, with 1.5 ms for Dy³⁺ and 6.5 ms for Sm³⁺, their dependence on glass matrix is remarkable similar. Fluoroaluminate glasses with varying phosphate content between 0 and 20 mol% (FPx), a pure phosphate glass (P100), and two borosilicate glasses with low (DURAN^®-like) and high optical basicity (NBS1) were used for investigations. A strongly ionic surrounding by fluorine ligands, as in fluoroaluminate glass samples, provides the longest fluorescence lifetime. It decreases with increasing phosphate content by increasing oxygen surrounding and with increasing RE³⁺ doping. Large differences were detected in the two borosilicate glasses depending on their optical basicity mainly due to differences in the Na₂O/B₂O₃ ratio. Duran-like samples with low Na₂O content have shown phase separation with higher doping concentration. The RE³⁺ ions are accumulated in the borate-rich droplets. Surprisingly only very low concentration-quenching effects were observed. In the opposite of NBS1 samples with high Na₂O content this generated extremely high quenching effect.     

Spectroscopic properties of Yb3+ ions in halogeno-sulfide glasses

In this work, we report the optical properties of Yb³⁺ ions in halogeno-sulfide glasses of composition (75 − x)GeS₂–25Ga₂S₃–xCsCl (x = 5%, 10%, 15%, 20%, and 25% CsCl). This study includes an analysis of the influence of halide concentration on the absorption and emission cross-sections and lifetimes of Yb³⁺ ions. A blue shift of the absorption and emission bands and a decrease of the absorption and emission cross-sections and transition probability are observed as the halide concentration increases in the glass.     

Alkaline earth zinc borate glasses doped with Cu2+ ions studied by EPR,optical and IR techniques

Copper ions incorporated into alkaline earth zinc borate glasses 10RO + 30ZnO + 60B₂O₃ (R = Mg, Ca and Sr) and 10SrO + (30 ? x)ZnO + 60B₂O₃ + xCuO (x = 0, 0.1, 0.3, 0.5, and 0.7 wt.%) were characterized by electron paramagnetic resonance (EPR), optical absorption and FTIR techniques. The EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu²⁺ ions. The values of spin-Hamiltonian parameters indicate that the Cu²⁺ ions in alkaline earth zinc borate glasses were present in octahedral sites with tetragonal distortion. The spin concentration (N) participating in resonance was calculated as a function of temperature for strontium zinc borate (SrZB) glass sample containing 0.7 wt.% of Cu²⁺ ions and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility (χ) was calculated at different temperatures and the Curie constant was evaluated from the 1/χ-T graph. The optical absorption spectra of these samples show only one absorption band. The optical band gap energies (E_g) and Urbach energy (ΔE) are calculated from their ultraviolet edges. The FTIR studies show different stretching and bending vibrations of alkaline earth zinc borate glasses.     

Photoluminescence properties of Sm3+-doped SFB glasses for efficient visible lasers

The photoluminescence properties of different concentrations of Sm³⁺ ions doped sodium fluoroborate (SFB) glasses of composition Na₂O–LaF₃–CaF₂–AlF₃–B₂O₃–SmF₃ have been investigated. The energy level analysis is carried out using free-ion Hamiltonian model. The Judd–Ofelt intensity parameters are used to evaluate the laser characteristic parameters such as spontaneous transition probability, radiative lifetime and fluorescence branching ratio for ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2 and 11/2) emission transitions of Sm³⁺ ion. The principal photoluminescence transitions of interest are identified by recording the emission spectra for different Sm³⁺ ion concentrations and measuring their emission cross-sections, integrated absorption cross-sections and optical gain parameters. The decay profiles from the ⁴G_7/2 excited manifold state to its lower lying energy levels have been recorded by monitoring the excitation and emission wavelengths at 402 and 600 nm, respectively. The dependence of effective fluorescence lifetime on the Sm³⁺ concentration is also discussed.     

Characterization of Eu3+-doped fluorophosphate glasses for red emission

Fluorescence spectra and decay curves of the ⁵D₀ level for different concentrations of Eu³⁺ (4f⁶) ions in K–Ba–Al fluorophosphate glasses have been measured at room temperature and are analyzed. The Judd–Ofelt intensity parameters Ω₂ and Ω₄ have been determined from the intensity ratios of emission peaks corresponding to ⁵D₀ → ⁷F_J (J = 2 and 4) to ⁵D₀ → ⁷F₁ transitions for 1.0 mol% glass. The intensity parameters thus obtained are in turn used to calculate the radiative properties of the fluorescent levels of Eu³⁺ ions. Second and fourth rank crystal-field parameters have been evaluated by assuming a C_2V site symmetry for the local environment of Eu³⁺ ions to estimate the crystal-field strength experienced by Eu³⁺ ions in the present host. The decay profiles of the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions in the present glasses are found to be single exponential for all the studied Eu³⁺ ion concentrations. A marginal increase in lifetime of the ⁵D₀ level has been noticed with Eu³⁺ ion concentration up to 2.0 mol% and then the lifetime marginally decreases for higher Eu³⁺ ion concentrations.     

Crystallization behavior of Dy3+-doped selenide glasses

Rare earth (RE)-doped chalcogenide glasses are an important promising material for active photonic devices, including mid-infrared (mid-IR) fiber lasers and amplifiers. Here we report on dysprosium ion (Dy³⁺)-doped GeAsGaSe chalcogenide glasses based on 10 atomic (at.) % Ga. A series of Dy³⁺-doped GeAsGaSe glasses, with increasing levels of Dy³⁺ dopant from 0 ppm to 2000 ppm added to the Ge_16.5As₉Ga₁₀Se_64.5 (at. %) base glass, is synthesized and characterized using: Fourier transform infrared spectrometry; X-ray diffraction (XRD); imaging and analysis using a high resolution transmission electron microscope, with selected area electron diffraction (HRTEM-SAED), and energy dispersive X-ray spectroscopy (HRTEM-EDX) and an environmental scanning electron microscope with energy dispersive X-ray spectroscopy (ESEM-EDX) and with secondary electron mapping. At the higher levels of Dy³⁺ doping, the glasses exhibit bulk crystallization; XRD, HRTEM-EDX and ESEM-EDX indicate the crystals are predominantly a modified, face centered cubic α-Ga₂Se₃, with some substitution of Ge. In addition, features on the bulk glass surface are shown to comprise Dy³⁺, sometimes accompanied by Si and [O] which, it is suggested, are due to contamination from the silica glass melting ampoule.     

EPR and magnetic susceptibility studies of B2O3–Bi2O3–Gd2O3 glasses

Glasses of the xGd₂O₃ · (100 − x)[B₂O₃ · Bi₂O₃] system with 0.5 ⩽ x ⩽ 10 mol% were studied by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. Data obtained show that for low gadolinium oxide contents of the samples (x ⩽ 3 mol%) the Gd³⁺ ions are randomly distributed in the host glass matrix and are present as isolated and dipole–dipole coupled species. For higher gadolinium oxide contents of the samples (x > 3 mol%) the Gd³⁺ ions appear as both isolated and antiferromagnetically coupled species. The EPR spectra of the glasses reveal resonance sites with an unexpected high crystalline field in addition to the ‘U’ spectrum, typical for Gd³⁺ ions in disordered systems. This absorption line is due to Gd³⁺ ions that replace Bi³⁺ ions from the host glass matrix and could play the network unconventional former role in the studied glasses.     

Emission properties and local structure of Tm3+ in Ge–Ga–S–Br glass

Spectroscopic properties of Tm³⁺ in (1 − x) (Ge_0.25Ga_0.10S_0.65)–xBr (or CsBr) glasses (x = 0.0 and 0.1) were investigated. Emission properties of Tm³⁺ in 0.9(Ge_0.25Ga_0.10S_0.65)–0.1Br glass were similar to those in Ge_0.25Ga_0.10S_0.65 glass, while there was significant improvement when doped into 0.9(Ge_0.25Ga_0.10S_0.65)–0.1CsBr glass. The lifetime of the Tm³⁺:³H₄ level increased from 0.23 to 1.22 msec with 10 mol% CsBr addition. The presence of Cs⁺ facilitated the formation of [GaS_3/2Br]⁻ units by donating an electron to the Ga tetrahedron, resulting in the homogeneous distribution of Br. In this way, Tm³⁺ ions have their local environment made of Br only. When Br ions were added instead of CsBr, [GaS_(4−x)/2Br]⁻ units with x > 1 were formed and Tm³⁺ ions were surrounded by both S and Br, producing a high phonon environment.     

Photoluminescence of Sm3+, Dy3+, and Tm3+-doped transparent glass ceramics containing CaF2 nanocrystals

Photoluminescence properties of Sm³⁺, Dy³⁺, and Tm³⁺-doped transparent oxyfluoride silicate glass ceramics containing CaF₂ nanocrystals were reported. Emission bands of ⁴G_5/2 → ⁶H_5/2 (562 nm), ⁴G_5/2 → ⁶H_7/2 (598 nm), ⁴G_5/2 → ⁶H_9/2 (645 nm) and ⁴G_5/2 → ⁶H_11/2 (706 nm) for the Sm³⁺: glass and glass ceramic, with an excitation at ⁶H_5/2 → ⁴F_7/2 (402 nm) have been recorded. Of them, ⁴G_5/2 → ⁶H_7/2 (598 nm) has shown a bright orange emission. With regard to the Dy³⁺: glass, a bright fluorescent yellow emission at 575 nm (⁴F_9/2 → ⁶H_13/2) and blue emission at 481 nm (⁴F_9/2 → ⁶H_15/2) have been observed, apart from 662 nm (⁴F_9/2 → ⁶H_11/2) emission transition with an excitation at 386 nm (⁶H_15/2 → ⁴I_13/2 + ⁴F_7/2) wavelength. Emission bands of ¹G₄ → ³F₄ (650 nm) and ¹G₄ → ³H₅ (795 nm) transitions for the Tm³⁺: glass and glass ceramic, with an excitation at ³H₆ → ¹G₄ (467 nm) have been observed. Of them, ¹G₄ → ³F₄ (650 nm) has shown bright red emission. Decay lifetime measurements were also carried out for all the observed Sm³⁺, Dy³⁺, and Tm³⁺-doped glass and glass ceramic emission bands.     

Systematic study of spectroscopic properties and thermal stability of lead germanate glass doped with rare-earth ions

Glasses with composition 50GeO₂–(50?x)PbO–5PbF₂–xLnF₃ (Ln = Pr³⁺–Yb³⁺) were prepared from commercial raw materials. The content of PbF₂ was constant and amounted to 5 mol% whereas the concentration of luminescent ions was diverse (0.2 and 2 mol%). Thermal stability of the glasses were monitored by differential thermal analysis (DTA). It has been found that increase of rare-earth fluoride content from 0.2 mol% to 2 mol% brings about a shift of the glass crystallization onset from 450 °C to 487 °C for Nd-doped samples and from 466 °C to 482 °C for Tm-doped samples. Optical absorption and emission spectra of Ln active ions in oxyfluoride glass have been investigated at room temperature in the ultraviolet (UV), visible (VIS) and near-infrared (NIR) region. Oscillator strengths, phenomenological Judd–Ofelt intensity parameters Ω_2,4,6, radiative transition probabilities, branching ratios and radiative lifetimes of luminescent levels have been estimated. Analysis of decay curves of luminescence revealed that the increase of rare-earth fluoride content from 0.2 mol% to 2 mol% shortens the lifetime of the ⁴F_3/2 level of Nd³⁺ from 224 μs to 90 μs.     

Optical properties of Er3+-doped alkali fluorophosphate glasses

A systematic study of the optical absorption and luminescence spectra of Er³⁺-doped alkali fluorophosphate glasses (RTFP) 50(NaPO₃)–10TeO₂–20AlF₃–19RF–1Er₂O₃ (R = Li, Na and K) has been performed. The phenomenological Judd–Ofelt intensity parameters have been determined from the spectral intensities of the absorption bands in order to calculate the radiative transition probabilities, radiative lifetimes and branching ratios for various excited luminescent states. Using the visible and near infrared emission spectra, full width at half maximum (FWHM), emission cross-sections (σ_e) and figure of merit (FOM) were evaluated and compared with other hosts. Especially, the numerical values of these parameters indicate that the emission transition ⁴I_13/2 → ⁴I_15/2 transition at 1.534 μm in Er³⁺-doped fluorophosphate glasses may be highly useful in optical communication. The decay characteristic of ⁴S_3/2 excited level has also been recorded and analyzed. The calculated and experimental lifetimes were compared in terms of quantum efficiencies and multiphonon relaxation rates.     

Fabrication of Sm2+-doped macroporous aluminosilicate glasses with high alumina content

Macroporous Al₂O₃–SiO₂ glasses doped with Sm²⁺ have been prepared from a sol–gel system containing aluminum sec-butoxide, tetramethoxysilane, samarium chloride hexahydrate, poly(ethylene oxide), nitric acid, and water. Monolithic gels having interconnected macropores and skeletons are formed by inducing the phase separation parallel to the gelation. The use of aluminum sec-butoxide preheated at 80 °C as the starting material enables the incorporation of Al³⁺ into the gel skeleton up to 20 mol% in cation ratio. The maximum amount of Al³⁺, i.e., 20 mol%, is twice as large as that reported in our previous study, where aluminum sec-butoxide was diluted with sec-butanol prior to the hydrolysis. Heat-treatment of Sm³⁺-doped 20AlO_3/2 · 80SiO₂ macroporous glass under the reducing atmosphere converts Sm³⁺ to Sm²⁺, which is confirmed by the appearance of intense emission peaks attributed to 4f–4f transitions of Sm²⁺.     

Chemical co-precipitation of hybrid precursors to synthesize Eu3+/Dy3+ activated YNbxP1−xO4 and YNbxV1−xO4 microcrystalline phosphors

A modified wet-chemical synthesis technology was put forward to fabricate Eu³⁺/Dy³⁺ doped with YNb_xP_1−xO₄ and YNb_xV_1−xO₄ phosphors with varying x from the assembly of multicomponent hybrid precursors. The morphologies have been found to be 1–2 μm crystalline spheres using XRD and SEM. The red photoluminescence intensity reaches the strongest in YNb_0.8P_0.2O₄:Eu³⁺ and YNb_0.1V_0.9O₄:Eu³⁺ phosphors and the red to orange intensity ratio (RO) values decrease with the content of P(V) increasing. Besides this, the optimum concentration for Dy³⁺ luminescence in YNb_0.5P_0.5O₄ is 1 mol%, while that in YNb_0.5V_0.5O₄ is 0.5 mol% or lower than 0.5 mol%. The yellow to blue intensity ratio (YB) value of Dy³⁺ increases when the Dy³⁺ concentration increases from 0.5 to 8 mol% in YNb_0.5P_0.5O₄; however, that of Dy³⁺ does not vary much in YNb_0.5V_0.5O₄ matrix.     

Effect of heat treatment on Er3+ containing multicomponent oxyfluoride lead borate glass system

Effect of heat treatment on Er³⁺ containing multicomponent oxyfluoride lead borate glasses in (72 ? x)PbO–xPbF₂–18B₂O₃–6Al₂O₃–3WO₃–1ErF₃ (where x = 9 or 72) system have been studied. The samples with low and high PbF₂ concentrations were analyzed using X-ray diffraction and luminescence spectroscopy. Several narrowed and relatively intense diffraction lines have been formed after heat treatment attributed to the orthorhombic PbF₂ phase. Luminescence spectroscopy revealed bands due to ⁴I_13/2–⁴I_15/2 and ⁴S_3/2–⁴I_15/2 transitions of Er³⁺ ions. This observation makes these glasses candidates for NIR laser active media and up-conversion applications.     

White light emission from Eu3 +/Tb3 +/Tm3 + triply-doped aluminoborate glass excited by UV light

The Eu^3 +/Tb^3 +/Tm^3 + triply-doped glasses with the composition of CaO―Al₂O₃―B₂O₃―RE₂O₃ (RE = Eu,Tb,Tm) have been synthesized by melt quenching method. The photoluminescence of these Eu^3 +/Tb^3 +/Tm^3 + triply-doped glasses (CaAlB:RE^3 +) were studied and the emission spectra combining with blue, green and reddish orange bands were observed. Under 360 nm wavelength excitation the white light emission is achieved when the concentration (x) of Tm^3 + in Ca_0.931 ?xAlB:Eu^3 +_0.038,Tb^3 +_0.031,Tm^3 +_x glass is in the range of 0.0013-0.011 per mol matrix. In addition, the energy transfer (ET) between Tb^3 + and Eu^3 + ions in Eu^3 +/Tb^3 +/Tm^3 + triply-doped glasses was validated and the electric dipole–dipole interaction is responsible for the ET process of Tb^3 + → Eu^3 + at low concentrations. Hence, the Eu^3 +/Tb^3 +/Tm^3 + triply-doped aluminoborate glass could be a potential candidate for white LEDs.     

Glasses in the SbPO4–WO3 system

Glasses in the binary system (100 − x)SbPO₄–xWO₃ (20 ⩽ x ⩽ 60, x in mol%) have been prepared and characterized. Differential thermal analysis (DTA) shows that the glass transition temperature, T_g, increases from 412 °C, for samples containing 20 mol% of WO₃, to 481 °C observed for glass containing 60 mol%. Sample containing 40 mol% in WO₃ were observed to be the most stable against devitrification. The structural organization of the glasses has been studied by using Fourier transform infra-red (FTIR), Raman, ³¹P Magic angle spinning (MAS) and spin echo nuclear magnetic resonance (NMR) spectroscopies. Results suggest two distinct networks comprising the glass structure, one with high SbPO₄ content and the other characteristic of the highest WO₃ content samples. The glasses present photochromic properties. Colour changes are observed for samples after exposure to ultraviolet or visible laser light. XANES, at L₁ absorption edge of tungsten, suggests partial reduction from W⁶⁺ to W⁵⁺ species during the laser irradiation. The photochromic effects and the colour changes, promoted by laser excitation, are reversible and easily removed by heat for during 1 h at 150 °C. Subsequent ‘write/erase’ cycles can be done without degradation of the glasses.     

Optical properties and infrared-to-visible upconversion in Er3+-doped GeO2–Bi2O3 and GeO2–PbO–Bi2O3 glasses

Luminescence properties and upconversion studies of germanate glasses in ternary GeO₂–PbO–Bi₂O₃ and binary GeO₂–Bi₂O₃ systems containing Er₂O₃ (0.1–1.0 wt%) are presented for the first time. The Judd-Ofelt parameters found for these glasses are: Ω₂ = 4.50 × 10⁻²⁰ cm², Ω₄ = 1.55 × 10⁻²⁰ cm² and Ω₆ = 0.69 × 10⁻²⁰ cm² for binary glasses and Ω₂ = 4.44 × 10⁻²⁰ cm², Ω₄ = 1.82 × 10⁻²⁰ cm² and Ω₆ = 0.39 × 10⁻²⁰ cm² for ternary glasses. The refractive index of these glasses is found to be ∼2. The transition ⁴I_13/2 → ⁴I_15/2 is peaked at ∼1.53 μm and shows a radiative lifetime around 5 ms. Both systems exhibit similar emission cross-section at 1.53 μm around 0.8 × 10⁻²⁰ cm². Upconverted green emission at ∼530 nm (²H_11/2 → ⁴I_15/2) and ∼550 nm (⁴S_3/2 → ⁴I_15/2) and red emission at ∼668 nm (⁴F_9/2 → ⁴I_15/2) are observed under 980 nm cw excitation. Our results suggest that these glasses are promising candidates for applications in photonics.     

Structure of binary neodymium borate glasses by infrared spectroscopy

Using fast roller quenching techniques, a new series of binary rare earth oxide borate glasses were synthesized, with general formula xNd₂O₃ + (1 − x)B₂O₃, where x varies up to 35 mol%. The glasses were investigated by using mid infrared reflectance spectroscopy. The results show that the neodymium acts as a modifier, similar to an alkali metal. As x is increased, the borate glass network is shown to change from a three-coordinated to four-coordinated boron system. The results are further investigated by analyzing the spectra in terms of the location of the bands to show how the borate groups change upon neodymium addition.     

Glass composition dependence of luminescence due to Ge2+ center in germanate glasses

Germanate glasses were prepared by the melt-quenching method using an assembled hot-thermocoupler equipped in a sample chamber of a fluorescence spectrometer, and subsequently their luminescence and excitation spectra were measured. In the GeO₂ glass, luminescence bands due to the Ge²⁺ center appeared at the central wavelengths of 300 and 395 nm, their excitation bands being at 250 and 330 nm, respectively. In the (100 − x)GeO₂ − xM_mO_n glasses, for M_mO_n = B₂O₃ (x ≦ 50), SiO₂ (x ≦ 40), and Al₂O₃ (x ≦ 2), the luminescence intensity and therefore the amount of the Ge²⁺ center increased with increasing the content of M_mO_n, where M^(2n/m)+ ions (B³⁺, Si⁴⁺, and Al³⁺) have lower basicities than a Ge⁴⁺ ion. Contrarily, for M_mO_n = Li₂O (x ≦ 30), Na₂O (x ≦ 20), K₂O (x ≦ 20), CaO (x ≦ 20), SrO (x ≦ 3), BaO (x ≦ 15), ZnO (x ≦ 20), Ga₂O₃ (x ≦ 10), Sb₂O₃ (x ≦ 20), Bi₂O₃ (15 ≦ x ≦ 25), TiO₂ (x ≦ 3), and Nb₂O₅ (x ≦ 10), the luminescence intensity and the amount of the Ge²⁺ center rapidly decreased with increasing the amount of additives and disappeared, where M^(2n/m)+ ions (Li⁺, Na⁺, K⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, Ga³⁺, Sb³⁺, Bi³⁺, Ti⁴⁺, and Nb⁵⁺) have higher basicities than a Ge⁴⁺ ion.     

The densities of mixed glass former 0.35 Na2O + 0.65 [xB2O3 + (1 − x)P2O5] glasses related to the atomic fractions and volumes of short range structures

The mixed glass former effect (MGFE) is defined as a non-linear and non-additive change in the ionic conductivity with changing glass former fraction at constant modifier composition between two binary glass forming compositions. In this study, mixed glass former (MGF) sodium borophosphate glasses, 0.35 Na₂O + 0.65 [xB₂O₃ + (1 ? x)P₂O₅], 0 ≤ x ≤ 1, which have been shown to have a strong positive MGFE, have been prepared and their physical properties, density and molar volume, have been examined as predictors of structural change. The density exhibits a strong positive non-linear and non-additive change in the density with x and a corresponding negative non-linear and non-additive change in the molar volume. In order to understand the structural origins of these changes, a model of the molar volume was created and best-fit to the experimentally determined molar volumes in order to determine the volumes of the short range order (SRO) structural units in these glasses, how these volume change from the molar volumes of the binary glasses, and how these volumes change across the range of x in the ternary glasses. The best-fit model was defined as the model that required the smallest changes in the volumes of the ternary phosphate and borate SRO structural groups from their values determined by the densities of the binary sodium phosphate and sodium borate glasses. In this best-fit molar volume model, it was found that the volumes of the various phosphate and borate SRO structural groups decreased by values ranging from a minimum value of ~ 1% for x = 0.1 and 0.9 to a maximum value of ~ 6% for the phosphate and ~ 9% for the borate SRO groups at the minimum in molar volume at x = 0.4. The free volume was found to have a negative deviation from linear which is unexpected given the positive deviation in ionic conductivity.