5d Transitions Research Articles

Red luminescence from La2O3:Eu3+ nanophosphor prepared by Sol-Gel method

Pure and Eu3+ doped La2O3 nanophosphor was synthesized by sol gel process. PL spectra of undoped La2O3 samples shows broad emission peaks between 400 and 600 nm and Eu3+ doped samples show PL emission peaks at 510, 515, 531, 537, 553, 578, 585, 594, 612 and 624 nm. These peaks are attributed to 5D1 → 7F2, 5D1 → 7F2, 5D0 → 7F0, 5D0 → 7F1,5D0 → 7F2 transitions of Eu3 + ions. The electronic dipole transition corresponding to5D0 → 7F2 (624, 612 nm) is stronger than the magnetic dipole transition of 5D0 → 7F1 (585, 594 nm) of Eu3+ ions. Luminescence behavior of Eu3+ in La2O3 is analyzed by Judd–Ofelt intensity parameters.

Excited-State Dynamics during Primary C-I Homolysis in Acetyl Iodide Revealed by Ultrafast Core-Level Spectroscopy.

In typical carbonyl-containing molecules, bond dissociation events follow initial excitation to nπC═O* states. However, in acetyl iodide, the iodine atom gives rise to electronic states with mixed nπC═O* and nσC-I* character, leading to complex excited-state dynamics, ultimately resulting in dissociation. Using ultrafast extreme ultraviolet (XUV) transient absorption spectroscopy and quantum chemical calculations, we present an investigation of the primary photodissociation dynamics of acetyl iodide via time-resolved spectroscopy of core-to-valence transitions of the I atom after 266 nm excitation. The probed I 4d-to-valence transitions show features that evolve on sub-100-fs time scales, reporting on excited-state wavepacket evolution during dissociation. These features subsequently evolve to yield spectral signatures corresponding to free iodine atoms in their spin-orbit ground and excited states with a branching ratio of 1.1:1 following dissociation of the C-I bond. Calculations of the valence excitation spectrum via equation-of-motion coupled cluster with single and double substitutions (EOM-CCSD) show that initial excited states are of spin-mixed character. From the initially pumped spin-mixed state, we use a combination of time-dependent density functional theory (TDDFT)-driven nonadiabatic ab initio molecular dynamics and EOM-CCSD calculations of the N4,5 edge to reveal a sharp inflection point in the transient XUV signal that corresponds to rapid C-I homolysis. By examining the molecular orbitals involved in the core-level excitations at and around this inflection point, we are able to piece together a detailed picture of C-I bond photolysis in which d → σ* transitions give way to d → p excitations as the bond dissociates. We also report theoretical predictions of short-lived, weak 4d → 5d transitions in acetyl iodide, validated by weak bleaching in the experimental transient XUV spectra. This joint experimental-theoretical effort has thus unraveled the detailed electronic structure and dynamics of a strongly spin-orbit coupled system.

Anomalous oxidation state of europium in the Sr3(PO4)2-type phosphors doped with alkaline cations

A series of new phosphors Sr2.98Eu0.01M0.01(PO4)2 (SEMP), M = Li+, Na+, K+ have been synthesized by high temperature solid state reaction. Powder X-ray diffraction study reveals that SEMP samples are isostructural to palmierite-type Sr3(PO4)2 phosphate. The anomalous reduction Eu3+ → Eu2+ in nonreduction media in Sr3(PO4)2 host has been reported for the first time. The blue emission from Eu2+ (∼425 nm) corresponding to the 4f65d1→4f7(8S7/2) transitions and red emission from Eu3+ (550–750 nm), corresponding to the 4f–4f transitions 5D0 → 7FJ (J = 0−4) were observed. The highest Eu3+ luminescence intensity was observed for Li+-doped host both at 296 K and at 10 K. The results show that the synthesized samples with tunable blue/red-orange emission can be considered for thermal sensing application.

Synthesis, Photoluminescent Characteristics and Eu3+-Induced Phase Transitions in Sr3Zr2O7:Eu3+ Red Phosphors.

Designing phosphors that are excited by blue light is extraordinarily important for white light-emitting diodes (w-LEDs). In the present study, a new Ruddlesden-Popper type of SZO:xEu3+ (x = 0.01~0.10) phosphors was developed using solid-state reactions. Interestingly, a Eu3+ doping-induced phase transformation from the Sr3Zr2O7 (cubic) to the SrZrO3 (orthorhombic) phase was observed, and the impact of the occupied sites of Eu3+ ions on the lifetime of Sr3Zr2O7:xEu3+ phosphors is discussed in detail. Diffuse reflectance spectroscopy results showed that the band gap of SZO:xEu3+ phosphors gradually increased from 3.48 eV for undoped Sr3Zr2O7 hosts to 3.67 eV for SZO:0.10Eu3+ samples. The fluorescence excitation spectrum showed that ultraviolet (300 nm), near-ultraviolet (396 nm) and blue light (464 nm) were all effective excitation pump sources of Sr3Zr2O7:xEu3+ phosphors, and the strongest emission at 615 nm originated from an electric dipole transition (5D0→7F2). CIE coordinates moved from orange (0.5969, 0.4267) to the reddish-orange region (0.6155, 0.3827), and the color purity also increased. The fabricated w-LED was placed on a 460 nm chip with a mixture of YAG:Ce3+ and SZO:0.1Eu3+ samples and showed "warm" white light with a color rendering index (CRI) of 81.8 and a correlation color temperature (CCT) of 5386 K, indicating great potential for application in blue chip white LEDs.

НОВЫЕ ДАННЫЕ ОБ ОСОБЕННОСТЯХ ЛОКАЛЬНОЙ СТРУКТУРЫ ТВЕРДОГО РАСТВОРА Ca9La(PO4)7(1-x)(VO4)7x:Eu3+(1 %)

Solid solutions of phosphate-vanadates Ca9La(PO4)7(1–x)(VO4)7x:Eu3+(1 %) with the structure -Ca3(PO4)2 activated by europium were synthesized by the standard solid-phase method. It is shown that a continuous series of solid solutions is formed upon substitution P5+ → V5+. At the same time, the study by the second harmonic generation method showed that a symmetry inhomogeneity is observed in the series. When studying the luminescent properties, standard transitions of the europium cation with the dominant electric dipole transition 5D0 → 7F2 were found. The most intense emission was demonstrated by compositions with a centrosymmetric structure.

Synthesis and emission characteristics of rare earth ions (Eu3+ and Tb3+) doped calcium orthogermanate phosphors

In this study, rare earth ions (Eu3+ and Tb3+) doped calcium orthogermanate (Ca2GeO4) phosphors were synthesized through the high temperature solid-state route. PL (Photoluminescence), FTIR (Fourier transform infrared spectroscopy), SEM (Scanning electron microscopy), EDS (Energy dispersive spectroscopy) and PXRD (Powder X-ray diffraction) techniques were used to characterize all the prepared powder samples. The PXRD results of the samples give an orthorhombic phase system. The SEM-EDS measurements are used to confirm the doping of europium and terbium ions into the Ca2GeO4 lattice. The vibrational characteristics of the proposed phosphors are investigated from FTIR spectra. As per the PL studies, the Eu3+ and Tb3+ activated Ca2GeO4 phosphors are exhibited a prominent red emission at 610 nm and bright green emission at 547 nm under 244 nm and 229 nm excitation wave lengths respectively. The obtained results are ascribed to the ED (Electric Dipole) transition and MD (Magnetic Dipole) transitions 5D0 → 7F2 and 5D4 → 7F5 of europium and terbium ions respectively. The CIE diagram illustrates the emission colors of the synthesized phosphors which are given as red and green emission regions. Based on obtained results, the prepared phosphors may be suitable for solid state light and display devices.

Luminescence and photometric activity of an intense green emitting ZnBiBaBFTe:Tb3+ glasses

Borotellurite (ZnBiBaBFTe: ZnO + Bi2O3 + BaF2 + B2O3 + TeO2) glasses were fabricated by varying Tb2O3 concentration via the conventional melt and rapid quenching process. The glass stability (150 °C) and thermal stress (0.336) were evaluated using the differential thermal analysis. The rising value in the molar volume (39.69–43.86 cm3/mol) and field strengths (6.69–19.41 × 1015 cm−2) was due to the decrease in the density (2.932–2.804 gm/cm3) and inter-atomic distances (5.25 - 3.08 Å) of Tb3+ ions in ZnBiBaBFTe glasses. Measured excitation (PLE) and de-excitation (PL) spectra indicated that Tb3+:ZnBiBaBFTe glasses can be efficiently stimulated from 377 nm of UV radiation and exhibit a dazzle of green emission (543 nm) belonging to the transition 5D4→7F5 of Tb3+ ion. The radiative parameters of the level 5D4 of Tb3+ ion was predicted from the Ω2, 4, 6 intensity parameters by means of the JO (Judd-Ofelt) phenomenological formalism. Rise in Tb3+ concentration led to the enhancement of 5D4 emission transitions and reduction of lifetimes (2.24–1.82 ms) via dipole-dipole interaction. The detailed analysis of glasses revealed efficient lasing action parameters corresponds to branching ratio (> 60%), emission cross-section (14.61 × 10−22 cm2), gain bandwidth (15.34 × 10−28 cm3), and quantum efficiency (79%) along with photometric parameters like (x, y) color coordinates (∼0.29, 0.60), color purity (65%), and correlated color temperatures (∼6000 K) for green lasing applications.

Electronic structure and resonant inelastic x-ray scattering in GaTa4Se8

We have investigated the electronic structure of the lacunar spinel compound GaTa4Se8 within the density-functional theory (DFT) using the generalized gradient approximation while taking into account strong Coulomb correlations (GGA+U) in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. GaTa4Se8 can be classified as a Mott insulator since it was expected to be metallic from GGA band structure calculations in contradiction with the resistivity and optical measurements. Strong SOC splits the t2g-type manifold into a lower jeff = 3/2 quartet and an upper jeff = 1/2 doublet. The empty jeff = 1/2 band is well separated from the jeff = 3/2 one and almost completely given by linear combinations of d5/2 states. The partly filled jeff = 3/2 band is dominated by d3/2 states with some weight of d5/2 ones and consists of two groups of bands separated by an energy gap. The low energy jeff = 3/2 band situated at the Fermi level is very narrow, therefore even a small Hubbard U opens the energy gap. We have investigated theoretically the resonant inelastic x-ray scattering (RIXS) spectra at the Ta L2,3 edges. The calculated results are in good agreement with experimental data. We have found that the best agreement between the theory and experiment in the value of the Hubbard energy gap and RIXS spectra at the Ta L2,3 edges can be achieved for Ueff = 1.0 eV. The experimentally measured RIXS spectrum of GaTa4Se8 at the Ta L3 edge in addition to the elastic scattering peak at 0 eV possesses a sharp feature below 1 eV corresponding to transitions within the Ta t2g levels. The excitation located from 1 eV to 2 eV is due to t2g→eg transitions. The third wide very intensive structure from 2.8 eV up to 12 eV is almost completely derived from ligand-to-ligand charge transfer excitations. Such a situation is quite unique for the RIXS spectra in transition 5d metal systems. The origin of this dominant contribution as well as the electronic correlation in GaTa4Se8 is a consequence of its peculiar crystal structure which forms tetrahedral Ta4 clusters with very small intracluster Ta–Ta and Ta–Se distances and rather large distances between the Ta4 clusters. It results in the formation of localized electronic states and extremely strong Ta 5d - Se 4p hybridization which creates 5dSe states with high density of states. Such hybridization is much stronger in comparison with the corresponding 5d - O 2p hybridization in 5d transition metal oxides due to more extended Se 4p wave functions in comparison with oxygen 2p ones.

Novel orange-red phosphor Sr3Al2Si3O12:Eu3+ excited by ultraviolet or blue light with excellent thermal stability and color purity

It is still a challenge to develop orange-red phosphors with high performance, good thermal stability and high color purity. We successfully designed and synthesized aseries of novel orange-red phosphors Sr3-2xAl2Si3O12:xEu3+,xLi+ (0.04 ≤ x ≤ 0.18), which can be effectively excited by ultraviolet and bluelight. The fluorescence emission spectra of phosphors Sr3-2xAl2Si3O12:xEu3+,xLi+ are composed of several peaks at 500–750 nm, which belong to the electronic transition of 5D0→7FJ (J = 0,1,2,3,4) of Eu3+. Phosphor Sr2.8Al2Si3O12:0.1Eu3+,0.1Li+ has excellent thermal stability, when the temperature is as high as 418 K, the fluorescence emission intensity remains 77.81%, and the activation energy Ea = 0.2665 eV. The color coordinates of phosphors Sr3-2xAl2Si3O12:xEu3+,xLi+ are all located in the orange-red region (0.58,0.40), and the color purity is as high as 97.52%. These results show that phosphor Sr2.8Al2Si3O12:0.1Eu3+,0.1Li+ is a potential orange-red phosphor which can be effectively excited by ultraviolet light and blue light to obtain white light.

Luminescence kinetics of Eu<sup>3+</sup> ions in tungstates (Lu<sub>1 – <i>x</i></sub>Eu<sub><i>x</i></sub>)<sub>2</sub>(WO<sub>4</sub>)<sub>3</sub> and molybdates (Lu<sub>1 – <i>x</i></sub>Eu<sub><i>x</i></sub>)<sub>2</sub>(MoO<sub>4</sub>)<sub>3</sub>

The luminescence kinetics of the electron transition 5D0 → 7F2 (~613 nm) of Eu3+ ions has been studied in tungstates (Lu1 – xEux)2(WO4)3 and molybdates (Lu1 – xEux)2(MoO4)3. Luminescence decay times are very close in both compounds at x ≥ 0.2, while a significant difference is observed at x 0.1. Observed behavior is attributed to the difference in electronic structure of compounds.

Achieving bright green emission in Tb3+ doped ternary yttrate-based nanocrystalline powder for solid-state illumination applications

Tb3+ activated ternary yttrate-based nanophosphor series was fabricated via a simple solution combustion (SC) methodology. An orthorhombic crystal lattice havingspace group Pnma (62) with irregularly shaped particles with sizes between 32 and 54 nm was formed. Morphological features and elemental analysis were examined via TEM, SEM, and EDAX techniques, respectively. On near-ultraviolet (NUV) stimulation, luminescence spectra presented a bright green emission at 18315 cm−1 wavenumbers consistent with the electronic transition 5D4→7F5. The decay lifetimes, quantum efficiency, and non-radiative rates were also examined. The critical distance (Rc) originated to be 20.21 Å inducing the multipolar interrelations as the probable route for concentration quenching. The energy bandgap was examined via Diffuse Reflectance Spectroscopy (DRS). A brilliant luminescence profile is also replicated in green coordinates (0.2531, 0.4998) and 7479 K (color temperature), which has been committed to typical television, European-Broadcasting-Union (EBU), NICHIA-LED green coordinates, pc-WLEDs, and another solid-state lighting (SSL) applications.

Luminescence, CPL and magnetic properties of 1D enantiopure Ln3+ complexes with (S-) and (R-) α-methoxyphenylacetate ligand.

The reaction of Ln(NO3)2·6H2O (Ln = Eu, Tb, Dy and Sm) with (R)-(-)-α-methoxyphenylacetic acid (R-HMPA) and 1,10-phenanthroline (phen) in EtOH/H2O allows the isolation of 1D chiral compounds of formula [Ln(μ-R-MPA)(R-MPA)2(phen)]n in which Ln = Eu (R-Eu), Tb (R-Tb), Dy (R-Dy) and Sm (R-Sm). The same synthesis by using (S)-(+)-α-methoxyphenylacetic acid (S-HMPA) instead of (R)-(-)-α-methoxyphenylacetic acid allows the isolation of the enantiomeric compounds with formula [Ln(μ-S-MPA)(S-MPA)2(phen)]n where Ln = Eu (S-Eu), Tb (S-Tb), Dy (S-Dy) and Sm (S-Sm). Single crystal X-Ray diffraction measurements were performed for compounds R/S-Eu, R/S-Tb, S-Dy and S-Sm. The luminescence and the circular dichroism measured in the solid state are reported. All compounds show sensitized luminescence, notably the Eu3+ and Tb3+ ones, whose emission color can be perceived by the naked eye. For the Eu3+ and Tb3+ derivatives the quantum yield and the circular polarized luminescence have been measured. For the magnetic allowed transition 5D0 → 7F1 of the Eu3+ compound, the anisotropy factor glum is ±0.013 (+for S-Eu). Also, magnetic properties of all compounds were studied with the Dy3+ analogue showing slow relaxation of the magnetization under a direct current magnetic field of 1000 Oe.

Pure red-light emitting europium based complexes as efficient UV light converters: synthesis, crystal structure and photoluminescence properties.

This paper reports three new crystallographically characterized europium complexes with composition as follows: [Eu(fod)3(L1)] (1), [Eu(fod)3(L2)] (2) and [Eu(fod)3(L3)] (3) {L1 = benzimidazole (bzi), L2 = 4,7-diphenyl-1,10-phenanthroline (bath), L3 = 2-(2-pyridyl) benzimidazole (py-im) and fod = anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione (Hfod)}. The single crystal (SC) XRD analysis shows that complex 1 is seven-coordinated while complexes 2 and 3 are eight-coordinated with the geometrical structures of a mono-capped octahedron and a trigonal dodecahedron, respectively. The NMR spectra of the complexes validate the SC-XRD results in solution. The complexes are stable in solution as no dissociation of any ligand was observed in the NMR spectra of the complexes. The photophysical properties of the complexes in solution, solid state, and PMMA thin films were studied. The hypersensitive transition 5D0 → 7F2 dominates the emission spectra in all phases, showing the highly asymmetric environment around the Eu(III) ion. The bath ligand is found to be the best sensitizer of the Eu ion and hence complex 2 shows the strongest luminescence properties with the highest absolute quantum yield among the three complexes. The CIE coordinate analysis shows that pure red-luminescence is emitted by the Eu complexes in the solid state since the coordinates found in this phase are closer to the standard NTSC 1987 values. The optical band gaps were determined for the complexes and the observed values suggest that the complexes can have possible applications in the field of semiconductor materials.

Preparation and Photoluminescent Properties of Tb3+-Doped Lu2W3O12 and Lu2Mo3O12 Green Phosphors

Tungstate and molybdate phosphors have received great attention for their excellent photoluminescent properties and thermal stabilities. In the article, Tb3+-activated tungstate and molybdate green phosphors were prepared by a solid-state reaction method at different caline temperatures and were compared and studied. The crystal structures and the morphologies of samples were characterized by X-ray diffraction (XRD) patterns and field emission scanning electron microscopy (FE-SEM) images. The energy-dispersive spectra (EDS) proved the compositions of the prepared samples. The photoluminescence (PL) spectra showed that the PL excitation spectra of Tb3+-doped Lu2W3O12 and Lu2Mo3O12 green phosphors consisted of a broad and strong charge transfer band (CTB) and 4f–5d transitions of Tb3+ in the ultraviolet (UV) wavelength range and some narrowed excitation peaks from the 4f–4f transition of Tb3+ in the near ultraviolet (NUV) wavelength region. The PL emission spectra of the phosphors exhibited the characteristic green emissions owing to the 5D4→7F5 transition of Tb3+ located at about 547 nm. The values of energy gap Eg were calculated based on the diffuse reflection spectra (DRS). The measuring temperature-dependent PL spectra illustrated the thermal stabilities of phosphors. The Tb3+-doped Lu2Mo3O12 phosphor presented normal thermal quenching phenomena and the values of the thermal activation energy Ea were calculated based on the measuring temperature dependent PL emission spectra. The Tb3+-doped Lu2W3O12 phosphor exhibited abnormal thermal enhancing CTB excitation intensity at about 170 °C. Furthermore, the PL decay curves suggested that the lifetime corresponding to the 5D4 level of Tb3+ in the Lu2W3O12 host lattice was longer than that in the Lu2Mo3O12 host lattice. Compared the Tb3+-doped Lu2Mo3O12 phosphor, the Tb3+-doped Lu2W3O12 phosphor has shown potential as an application in temperature sensors.

Fine structure of 4f–5d absorption spectra of Me[formula omitted]-Yb[formula omitted] in the vacuum ultraviolet region under synchrotron excitation

Narrow dips were found in the excitation spectra of crystals of alkaline earth fluorides doped with ErF3 or/and YbF3. The positions of the dips are in good agreement with the positions of the narrow absorption lines Er3+, Yb3+ measured earlier. The absorption lines of the crystals were calculated from the excitation spectra. The observed dips in the excitation spectra are due to the absorption lines of 4f–5d transitions in lanthanide ions.

Photoluminescent and Photocatalytic Properties of Eu3+-Doped MgAl Oxide Coatings Formed by Plasma Electrolytic Oxidation of AZ31 Magnesium Alloy

The synthesis of Eu3+-doped MgAl oxide coatings containing MgO and MgAl2O4 was accomplished through plasma electrolytic oxidation of AZ31 magnesium alloy in aluminate electrolyte with the addition of Eu2O3 particles in various concentrations. Their morphological, structural, and above all, photoluminescent (PL) and photocatalytic activity (PA) were thoroughly investigated. PL emission spectra of MgAl oxide coatings feature characteristic emission peaks, which are ascribed to f–f transitions of Eu3+ ions from excited level 5D0 to lower levels 7FJ. The charge transfer state of Eu3+ or direct excitation of the Eu3+ ground state 7F0 into higher levels of the 4f-manifold are both attributed to the PL peaks that appear in the excitation PL spectra of the obtained coatings. The fact that the transition 5D0 → 7F2 (electrical dipole transition) in Eu3+-doped MgAl oxide coatings is considerably stronger than the transition 5D0 → 7F1 (magnetic dipole transition) indicates that Eu3+ ions occupied sites with non-inversion symmetry. Because of oxygen vacancy formation, the Eu3+-doped MgAl oxide coatings had a higher PA in the degradation of methyl orange than the pure MgAl oxide coating. The highest PA was found in Eu3+-doped MgAl oxide coating formed in an aluminate electrolyte with 4 g/L of Eu2O3 particles. The PA, morphology, and phase of Eu3+-doped MgAl oxide coatings did not change after several consecutive runs, indicating outstanding stability of these photocatalysts.

A novel red-emitting Na5W3O9F5:Eu3+ phosphor with high color purity for blue-based WLEDs

Red phosphor plays a key role in improving the lighting and display quality of phosphor-converted white light-emitting diodes (pc-WLEDs). Meanwhile, developing new luminescent matrix materials can positively contribute to the acquisition of ideal and efficient phosphors. In this work, we propose a novel red-emitting Na5W3O9F5:Eu3+ (NWOF:Eu3+) phosphor. The phase composition, morphology, electronic structure and photoluminescence properties of the NWOF:Eu3+ phosphor were systematically investigated. The EXAFS results prove that the Eu3+ dopants occupy the Na2 and Na3 sites in the NWOF host. Under 466 nm blue light excitation, NWOF:xEu3+ (0.05 ≤ x ≤ 0.25) phosphors display a dominant red emission at 607 nm and achieves a high color purity (97.44%) due to the dominant electric dipole transition (5D0→7F2) of Eu3+ ions. Impressively, this red-emitting NWOF:0.25Eu3+ phosphor exhibits relatively superior thermal stability (450 K, >50%) and excellent chromaticity stability (2.32 × 10−4 ≤ ΔE ≤ 6.23 × 10−3) from 298 K to 498 K. The activation energy for thermal quenching effect is determined to be 0.22 eV. Moreover, the pc-WLED was fabricated by coupling a 460 nm blue chip with the as-synthesized NWOF:0.25Eu3+ red phosphor and commercial YAG:Ce3+ phosphor. The optical parameters of the as-fabricated pc-WLED are also measured, and the CIE coordinates remain almost constant as the drive current increases from 20 mA to 120 mA. These results indicate that the NWOF:0.25Eu3+ red phosphors should be a suitable candidate as a red component for the preparation of pc-WLEDs.

Spectroscopic features of Tb3+ doped strontium zinc borate glasses for green laser applications

These days green laser is preferred as a flexible tool for welding direct bonded copper plates used in power electronics to improve electrification of automotive industry. As terbium is known for green emission, Tb3+ doped strontium zinc borate glasses are melt quenched. The broad hump in x-ray diffraction spectra revealed the amorphous nature. Structural modifications and stability of glasses was shown from fourier transform infrared spectra and differential thermal analysis traces. The Judd-Ofelt intensity parameters are calculated to realize the ligand environment among Tb3+ ions in host glass. The Tb3+ concentration dependent fluorescence properties in visible region and the non-radiative decay rates of 5D4→7F5 transition due to resonant energy transfer apart from intensity quenching of 5D3→7F5 transition in green region was studied. A strong peak registered at 542 nm for the transition 5D4→7F5 in the green region of emission spectra under the excitation of 378 nm. The radiative properties for the prominent luminescent transitions 4D5→7FJ (J=6,5,4,3) of Tb3+ ions are measured using Judd-Ofelt parameters. The values σe, βR,η (%), life- time decay and CIE co-ordinates for the transition 5D4→7F5 confirms that this transition is appropriate for potential green laser.

Opto-Dielectric Properties of TeO2-Li2O-LiCl-Eu2O3 Glasses

Europium oxide (Eu2O3) doped lithium tellurite glasses were prepared via melt quenching method. The effects of Eu2O3 doping at varying concentrations on the physical, electrical and optical properties of tellurite glasses were determined. The physical properties utilizing density and molar volume are determined. Electrical and dielectric constant in the 0.01–10 MHz frequency range was monitored as a function of temperature (298–398 K). At room temperature, the conductivity and activation energy increase with an increase in Eu2O3 concentration. Small polaron hopping (SPH) is used to explain the conduction mechanism. The density of the localized state is found to decrease with increasing Eu2O3 concentration in the range of 21.3 to 17.3 eV−1 cm−3. Dielectric parameters which are dielectric constant and loss tangent are found to increase with the increase in the concentration of Eu2O3. To study the spectroscopic properties of fabricated glasses, absorption and emission spectroscopy have been performed. UV–vis-NIR absorption spectra of glass samples divulged two significant peaks. Under the excitation of a 393 nm laser diode, six emission bands were observed in the Eu3+ single-doped glasses of which the peak at 613 nm corresponding to the transition 5D0 → 7F2 is highly intense for such glasses. Increasing intensity ratio ranging from 1.13 to 2.13 with increased Eu2O3 concentration is attributed to the low symmetry environment around Eu3+ ions. The findings of the current study can be used in advanced functional optoelectronic applications.

Red light component tuning by n-UV/blue light excitations in Sm3+/Eu3+ co-doped Y2O3–Al2O3–Bi2O3–B2O3–SiO2 glasses for W-LED applications

A series of single (Sm3+, Eu3+) and co-doped (Sm3+- Eu3+) Yttrium alumino bismuth borosilicate (YABiBS) glasses have been prepared by basic melting quench method and the emission properties of synthesized glasses were investigated. To analyze the optical and energy transfer mechanism of these glasses the characterizations viz, absorption and luminescence are done. The absorption spectral data is used to observe the electronic band structure by direct and indirect optical band gaps. Bonding Parameters (β‾,δ) were evaluated to explain the ionic (or) covalent nature of the metal-ligand bonds in the present glass network. Near ultraviolet (n-UV) and blue excitations such as 392 nm, 400 nm, 457 nm, and 488 nm are used to record the emissions of single (Sm3+) and co-doped (Sm3+-Eu3+) glasses to achieve the tuneable emissions. Sm3+ ions show the reddish-orange emission mainly through 4G5/2 → 6H7/2 (597 nm) and Eu3+ ions show the intense red emission of transition 5D0 → 7F2 (612 nm). For the Sm3+-Eu3+ glasses by using different excitations, we will achieve the emission changes from orange to reddish-orange and then to red. Decay curves were analysed to know the process of interaction involved in the energy transfer among co-doped RE3+ ions. CIE coordinates and CCT values for all the prepared glasses by various excitations were calculated.