Eu-doped Glass Research Articles

Spectroscopic properties and luminescence of the lithium tetraborate glasses co-doped with manganese and europium

High quality Li2B4O7:Mn,Eu glasses containing 1.0 mol.% MnO2 and Eu2O3 were prepared and investigated by XRD, EPR and optical spectroscopy techniques. Obtained data analysis shows that Mn is incorporated into the glass network as Mn2+ and Mn3+. Parameters of observed Mn2+ EPR signals in the Li2B4O7:Mn,Eu glasses were determined. Optical absorption spectrum of the studied glasses consists of broad band at 464 nm corresponding to the 5Eg(D) → 5T2g(D) transition of Mn3+ (3d4) ions and few narrow weak bands of the Eu3+ (4f6) ions. Emission spectra of the Li2B4O7:Mn,Eu glasses in orange-red region exhibit several sharp bands corresponding to the 5D0 → 7FJ (J = 0–4) transitions of Eu3+ ions and broad band belonging to the 4T1g(G) → 6A1g(S) transition of Mn2+ (3d5) ions. Comparative discussions were made on the luminescence spectra and decay curves of Mn2+ and Eu3+ ions in the Li2B4O7:Mn,Eu glasses and those in Mn-doped and Eu-doped glasses with the Li2B4O7 basic composition.

Luminescence performance of Eu3+ doped 25La2O3-60Al2O3-15ZrO2 glass prepared by containerless method

Rare-earth metal Eu doped glass 25La2O3-60Al2O3-15ZrO2:xEu3+ (x = 0.1 wt%, 0.5 wt%, 1.0 wt%, 3.0 wt% and 5.0 wt%) was prepared by gas suspension containerless laser melting technology, which is transparent and has sphere ball shape. The glass shows excellent thermal stability although the temperature difference ΔT between crystallization initiation temperature To and glass transition temperature Tg (ΔT=To-Tg) is just between 48.6 ℃− 64.9 ℃, showing low glass forming ability and being difficult to prepare glass by traditional melt-quenching method. The Eu-doped glass preserves rather high transparency, and presents enhanced mechanical performance due to the Eu3+ doping, which improves glass network connectivity. Strong orange emission peak centered at 605 nm and red emission peak at 696 nm, and weak yellow emission peak centered at 582 nm and red emission peak at 646 are engendered under the excitation of 394 nm light, attributing to the 5D0→7F2, 5D0→7F4, 5D0→7F1, and 5D0→7F3 electron energy level transitions of Eu, respectively. The 25La2O3-60Al2O3-15ZrO2:xEu3+ phosphor glass has strong nearly standard red light with high color purity, which presents excellent candidate for red luminescent phosphor and shows potential application in white-light-emitting diode.

Significant enhancement in Eu3+/Eu2+ emissions intensity by CdS quantum dots, in chloroborosilicate glasses

Eu3+ and CdS were singly doped and co-doped into chloroborosilicate glasses with composition 37.8SiO2–27B2O3–18BaO–3.6K2O–3.6Al2O3–10BaCl2 (mol%), by one-step melt quench technique. The samples were characterized by transmission electron microscopy (TEM), UV–Vis absorption, excitation, and emission spectroscopy. TEM images revealed the presence of CdS quantum dots (QDs) of size 5–20 nm in the CdS-doped glasses. The Eu-doped glass shows characteristic orange emission of Eu3+ at 393 nm excitation, while excitation at 250 and 317 nm revealed the existence of Eu2+ ions. There are strong evidences of energy transfer involving the charge transfer band (CTB) and different energy levels of Eu2+ and Eu3+ ions. The CdS-doped glass showed broad emission bands, originating from various electronic transitions involving defect and trap states in CdS crystalline structure. The emission band in the lower wavelength region, shows a red shift with increasing excitation wavelength, which proves the quantum confinement effect in CdS QDs. Eu/CdS co-doped glasses showed significant enhancements in Eu3+/Eu2+ emissions, up to 20 and 70 times, upon excitations at 393 and 317 nm, respectively, which is considerably higher compared to previously reported similar systems. This enhancement is attributed to a complex energy transfer occurring between Eu2+/Eu3+ and CdS QDs, reported for the first time in a glassy system, especially considering the in-situ growth of the QDs during melt. The co-doped glass also showed pure white emission at 6–7 nm slit width upon 387 nm excitation, which is a novel finding from an Eu/CdS co-doped glass.

An XAFS study of the local structure of Eu<sup>3+</sup> ions in glasses prepared by a levitation technique

The local structure around Eu3+ ions in Eu-doped glasses prepared by a levitation technique was analyzed by X-ray absorption fine structure spectroscopy. The X-ray absorption near edge structure spectra demonstrated that Eu3+ ions in Al2O3–SiO2 binary glasses were partly reduced during high-temperature melting. Extended X-ray absorption fine structure spectra indicated that in La2O3–Nb2O5, La2O3–Al2O3, and La2O3–TiO2 glasses that contained a large amount of La2O3, the bond lengths between Eu and O were distributed from 2.34 to 2.39 Å. The coordinated polyhedra around the Eu ions could be fitted to a single coordination sphere. It was found that the bond lengths tend to become shorter as the optical basicity of the glass increases. In the Al2O3–SiO2 glasses without any network modifiers, the local structure around the Eu was more complex, leading to the broader first correlation peak of radial structure function.

Luminescence properties and quantum efficiency of the Eu-doped borate glasses

The luminescence and radiative properties of the Eu-doped borate glasses with Li2B4O7, CaB4O7, and LiCaBO3 basic compositions have been investigated and analysed. The borate glasses of high chemical purity and optical quality, doped with Eu2O3 in amounts of 0.5 and 1.0 mol. % were obtained from the corresponding polycrystalline compounds in the air atmosphere using standard glass synthesis technology. The spectroscopic and radiative properties of obtained Eu-doped glasses were studied using electron paramagnetic resonance (EPR), optical absorption, photoluminescence (excitation and emission spectra, decay kinetics) techniques, and modified Judd–Ofelt analysis. The photoluminescence spectra of the Eu-doped borate glasses reveal intense emission bands, which correspond to the 5D0 → 7FJ (J = 0 ÷ 4) transitions of Eu3+ ions. The observed luminescence decay curves are satisfactory described in the framework of single exponential approximation with lifetimes, which lie in the 2.04 ÷ 2.26 ms range. The Judd–Ofelt intensity parameters (Ωλ) for Eu3+ centres in the investigated glasses were calculated from their luminescence emission spectra. Radiative lifetimes and internal quantum efficiencies were estimated for observed emission transitions of the Eu3+ centres in the investigated glasses. External quantum yield of luminescence was measured experimentally via an absolute method. The high calculated internal quantum efficiency (∼50%) and relatively high measured external quantum yield (∼11%) of the Eu3+ luminescence show that the Li2B4O7:Eu, CaB4O7:Eu, and LiCaBO3:Eu glasses belong to perspective luminescent materials.

Eu2 + promoted formation of molecule-like Ag and enhanced white luminescence of Ag/Eu-codoped oxyfluoride glasses

The Ag/Eu singly-doped and co-doped glasses were prepared with a melt-quenching method. Silver species are identified as Ag+, molecule-like Ag nano-clusters (Ag NCs) and Ag nano-particles (Ag NPs) with surface plasmonic resonance (SPR) behaviors in the Ag-doped glasses (GAg and GAgEu) by absorption and photoluminescence spectra. Europium ions, including Eu2+ and Eu3+, also existed in the Eu-doped glasses (GEu and GAgEu). The formation of Ag NCs was found to be effectively promoted by an accompanied oxidation of Eu2+. This significantly enhances the super-broad visible emission of the Ag/Eu co-doped glass (GAgEu) by about 8 times than the Ag-doped glass (GAg). Owing to energy transfer from silver species (Ag+ and Ag NCs) to Eu3+, the UV excitation of the Eu3+ red emission was enhanced and extended in 240nm– 400nm region. Combining the bluish white emission of Ag NCs and the red emission of Eu3+, the Ag/Eu co-doped glass (GAgEu) emits pure white light with a low color temperature (CCT) and a high color rendering index (CRI), thus can be a candidate for LED illumination.

Preparation method and thermal properties of samarium and europium-doped alumino-phosphate glasses

Abstract The present work investigates alumino-phosphate glasses from Li2O–BaO–Al2O3–La2O3–P2O5 system containing Sm3+ and Eu3+ ions, prepared by two different ways: a wet raw materials mixing route followed by evaporation and melt-quenching, and by remelting of shards. The linear thermal expansion coefficient measured by dilatometry is identical for both rare-earth-doped phosphate glasses. Comparatively to undoped phosphate glass the linear thermal expansion coefficient increases with 2 × 10−7 K−1 when dopants are added. The characteristic temperatures very slowly decrease but can be considered constant with atomic weight, atomic number and f electrons number of the doping ions in the case of Tg (vitreous transition temperature) and Tsr (high annealing temperature) but slowly increase in the case of Tir (low annealing temperature–strain point) and very slowly increase, being practically constant in the case of TD (dilatometric softening temperature). Comparatively to undoped phosphate glass the characteristic temperatures of Sm and Eu-doped glasses present lower values. The higher values of electrical conductance for both doped glasses, comparatively to usual soda-lime-silicate glass, indicate a slightly reduced stability against water. The viscosity measurements, showed a quasi-linear variation with temperature the mean square deviation (R2) being ranged between 0.872% and 0.996%. The viscosity of doped glasses comparatively to the undoped one is lower at the same temperature. Thermogravimetric analysis did not show notable mass change for any of doped samples. DSC curves for both rare-earth-doped phosphate glasses, as bulk and powdered samples, showed Tg values in the range 435–450 °C. Bulk samples exhibited a very weak exothermic peak at about 685 °C, while powdered samples showed two weak exothermic peaks at about 555 °C and 685 °C due to devitrification of the glasses. Using designed melting and annealing programs, the doped glasses were improved regarding bubbles and cords content and strain elimination.

Multi-wavelength excitable europium-doped borosilicate glasses for orange-red emission: composition-induced structure and valence variation

Europium-doped borosilicate glasses were prepared by melt-quenching procedure in the air. The mixed valence of Eu2+ and Eu3+ was identified by photo luminescence spectrum and electron paramagnetic resonance (EPR). The existence of mixed valence was observed owing to the unequivalent substitution and de-polymerization network of the as-prepared borosilicate glasses. The variation of the glass composition in B2O3/BaO ratios changed the stability of the Eu3+ ions distinctly. In particular, as-prepared borosilicate glasses exhibited a tri-wavelength light excitable spectra centered at 397, 466 and 534 nm to give the broadened orange-red emission at around 592 and 617 nm, due to supersensitive transitions of Eu3+ ions. This simultaneous tri-wavelength excitation happened to correspond with the emitting wavelength from near ultraviolet, blue AlInGaN chips and that from YAG:Ce3+. The total quantum yield (QY) of the Eu-doped glasses under 466 nm excitation was evaluated to be 10%, potentially providing a versatile combination with the europium-doped borosilicate glasses for red component addition to improve the quality of white light.

Structure and Optical Spectroscopy of Eu-Doped Glass Ceramics Containing GdF3 Nanocrystals

Transparent glass ceramics containing hexagonal GdF3 nanocrystals were fabricated by melt-quenching and subsequent heating of glass with composition of 44SiO2−28Al2O3−17NaF−11GdF3. The GdF3 nanocrystals with mean size of 6 nm were precipitated during quenching of the melt. Increasing the heating temperature of the quenched sample resulted in the further precipitation and growth of the GdF3 particles. The room temperature photoluminescence spectra of the glass ceramic excited at 398 nm show that, in addition to the characteristic sharp emissions of Eu3+ ions, an intense wide blue emission band ascribing to the Eu2+ 5d → 4f transition also appeared. The obvious Stark splitting of the emissions, the low forced electric dipole 5D0 → 7F2 transition, and the long decay lifetimes of Eu3+ evidenced the partition of Eu3+ ions into the GdF3 nanocrystals, while Eu2+ ions were found to reside in the glass matrix. The excitation and emission spectra demonstrated that the excitation energy of Gd3+ was transferred to bo...

Preparation and Fluorescent Property of Eu-Doped High Silica Glasses

A method to fabricate europium ions doped-high silica glass for transparent fluorescence materials based on the fabrication and sintering technique of nano-porous silica glass was reported. Glasses impregnated with Eu ions and sintered at above 1150 °C in a reduction atmosphere show a very strong blue light from an emission band at about 430 nm due to the 4f 65d→4f 7( 8S 7/2) transition of the Eu 2+ ions. On the other hand, the Eu-doped glass obtained by co-impregnated with Y 3+ and V 5+ ions and sintering in oxidation atmosphere behaves a very strong red emission band at about 615 nm with a UV excitation. An appearance of vanadate band in the excitation spectrum of Eu 3+, Y 3+ and V 5+ ions co-doped high silica glass implies an effective energy transferring from VO 4 3- to Eu 3+ and effective excitation of Eu 3+ by about 500 nm strong broad emission of VO 4 3-.

Electron Microprobe and Photoluminescence Analysis of Europium-Doped Gallium Nitride Light Emitters

ABSTRACTRare-earth doped GaN structures offer potential for optical devices emitting in the visible region [1,2]. We describe a study of MOVPE grown GaN-on-sapphire epilayers implanted with Europium ions, producing characteristic red emission lines between 540 and 680 nm due to intra-4f(n) electron transitions. As-implanted and subsequently annealed samples are investigated using a combination of wavelength dispersive x-ray analysis (WDX), electron microscopy, cathodoluminescence (CL) and photoluminescence (PL). WDX is shown to be a powerful technique for quantifying rare-earth concentrations in GaN, with varying electron beam voltages allowing a degree of depth profiling, further enhanced by the simultaneous collection of room temperature luminescence (CL) from the analysed region [3]. The intensities of the sharp lines observed in the luminescence spectrum are compared to the doping density (between 1014 – 1015 cm−2) and the Eu content measured by WDX, using a Eu-doped glass standard. Differences observed in the luminescence spectra produced by laser and electron beam excitation will be discussed along with the importance of the annealing conditions, which “heal” defects visible in the electron micrographs.

Optical properties of Europium doped gels during densification

Base catalyzed porous silica sol–gel monoliths fired at 1000°C were used to prepare Eu and Eu–Al co-doped glasses by post doping and subsequent densification around 1125–1150°C in air. Both Eu 3+ and Eu 2+ ions were found to coexist in densified Al co-doped glasses. The absorption, emission and excitation spectra of the Eu-doped glasses are significantly dependent on the alumina content. The densification temperature of the doped gel also played a major role in the reduction process. The UV excitation efficiency for the 5 D 0→ 7 F 2 transition of Eu 3+ ions (614 nm) was increased in the presence of Eu 2+ ions due to energy transfer from Eu 2+ to Eu 3+ ions.

Properties of laser-induced gratings in Eu-doped glasses.

The properties of permanent, laser-induced gratings were studied in ${\mathrm{Eu}}^{3+}$-doped glasses. These gratings are associated with a structural modification of the glass host in the local environment of the ${\mathrm{Eu}}^{3+}$ ions, and we have investigated the effects produced by altering the ${\mathrm{Eu}}^{3+}$ concentration and by changing the composition of the glass host. A two-level-system model is developed to explain the results.

LASER INDUCED REFRACTIVE INDEX GRATINGS IN EU3+GLASSES

Four wave mixing techniques are used to induce refractive-index gratings in Eu-doped glasses. When the Eu3+ ions are resonantly excited, superimposed transient and permanent gratings are formed. The former is characteristic of population grating, while the latter is attributed to local structural modifications of the glass host induced by high energy phonons localized around the Eu3+ ions. The result suggest the use of such gratings for de-multiplexing applications.

Thermal lensing and permanent refractive index changes in rare-earth-doped glasses

The characteristics of thermal lensing were measured for Eu3+- and Nd3+-doped phosphate glasses under resonant and nonresonant excitation conditions. The relative strengths and response times of the laser-induced lenses were determined and intepreted in terms of the thermal properties of the glass hosts for nonresonant excitation and the coupling of the rare-earth ions to the local vibrations for resonant excitation. Significant enhancement of the strength of thermal lensing was observed for resonant excitation, and this effect was much greater for the Eu-doped glass than for the Nd-doped glass. The response times for thermal lensing were also different for resonant and nonresonant excitation. In addition, a permanent change in the refractive index of Δn = 1.23 × 10−5 was observed for the Eu-doped glass and not for the Nd-doped glass. These results are discussed in terms of the different distributions of vibrational modes generated by the different types of laser excitation of these two rare-earth ions.

Relationship between laser-induced gratings and vibrational properties of Eu-doped glasses.

Four-wave-mixing techniques have been shown previously to produce permanent refractive index gratings in Eu-doped glasses by resonant excitation of the ${\mathrm{Eu}}^{3+}$ ions. A variety of glass hosts were studied and it was found that permanent holographic gratings could be established in some of these but not in others. We report here an extension of our previous work which includes investigations of new materials, attempts to form gratings with different excitation wavelengths, and a comparison of the Raman and resonant Raman spectra of glasses which do and do not exhibit permanent holographic gratings. It was found that direct excitation into the $^{5}\mathrm{D}_{0}$ level did not produce permanent gratings. It was also found that glasses which do exhibit permanent gratings have high-frequency vibrational modes which couple strongly to the ${\mathrm{Eu}}^{3+}$ ions. These results help to verify the model proposed previously to explain the origin of the holographic grating in terms of structural changes caused by thermal effects arising from radiationless relaxation through high-frequency local modes.

Laser-induced refractive-index gratings in Eu-doped glasses.

Four-wave-mixing techniques were used to establish and probe refractive-index gratings in ${\mathrm{Eu}}^{3+}$-doped silicate and phosphate glasses. When the ${\mathrm{Eu}}^{3+}$ ions are resonantly excited, superimposed transient and permanent gratings are formed. The former are characteristic of population gratings of excited ${\mathrm{Eu}}^{3+}$ ions while the latter are attributed to local structural modifications of the glass hosts. The time dependences of the grating buildup, decay, and erasure are reported as a function of temperature, laser power, and ``write''-beam crossing angle for each of the samples. The results suggest the use of laser-induced gratings in these glasses in applications such as amplitude-modulated phase-conjugate reflectors.