3d Levels Research Articles

Enhanced photoluminescence in CaMoO4:Eu3+ by Mn2+ co-doping

Phosphors doped with rare-earth elements have been extensively employed as white light emitting diodes (wLEDs). Red component is essential in realizing the warm white light efficiently. In this work, we report enhancement in red luminescence of Eu doped phosphor by transition metal doping. Here, a series of Eu3+ doped CaMoO4 and Mn+2/Eu3+ co-doped samples are synthesized successfully by facile auto combustion method. Structural and optical analyses of all samples are studied. UV–Vis analysis of Eu3+ doped CaMoO4 samples ascertains the red-shift in the absorption peak and peak broadening in Mn+2/Eu3+ co-doped CaMoO4. PL study shows an increase in the intensity of emission peaks at 610–630 nm and at 702–711 nm wavelength range up to 4 at % Eu3+ doped CaMoO4, which indicates effective energy transfer from Mo–O charge transfer band to 5D0 level of Eu3+. Luminescence intensity is further increased by Mn+2/Eu3+ co-doping in CaMoO4. For 0.3% at Mn+2 co-doping in CaMoO4:4Eu3+, it is observed that upon 290 nm excitation there is a decrease in the emission broadband around 425 nm–575 nm and increase in intensities of peaks at 612 nm, 615 nm, 654 nm, and 702 nm. Therefore, it is concluded that with proper tuning of Mn+2/Eu3+ doping in CaMoO4, prepared phosphor might have potential application in the fields of lighting and display.

Synthesis, Structure, Morphology, and Luminescent Properties of Ba2MgWO6: Eu3+ Double Perovskite Obtained by a Novel Co-Precipitation Method.

Eu3+ doped Ba2MgWO6 (BMW) double-perovskite was successfully synthesized for the first time by the co-precipitation method. The synthesis procedure, crystal structure, as well as morphology of obtained samples are presented. Domination of the 5D0–7F1 magnetic–dipole over forced electric–dipole transitions in the emission spectra indicates that Eu3+ ions are located in the high symmetry site with inversion center. Only one emission line assigned to the 5D0–7F0 transition was observed, confirming that europium substituted for only one host cation site. The photoluminescence excitation (PLE) spectrum is dominated by a strong and broad band related to the O2− → Eu3+ and O2− → W6+ charge transfer. The decay of the emission from the 5D0 and 5D1 levels was investigated. The temperature-dependent emission spectra showed that the T0.5 is equal to 350 K. Extinguishing mechanisms of the Eu3+ luminescence in the studied host are discussed.

High density tungsten gadolinium borate glasses doped with Eu3+ ion for photonic and scintillator applications

The melt quenching technique used to prepare tungsten gadolinium borate (Eu: WGdB) glasses doped with different concentrations of Eu3+ ions. The structural and spectroscopic analysis have been carried out by density, molar volume, X-ray absorption spectroscopy (XAS), UV-VIS-NIR absorption, excitation, emission spectra and decay time measurements. The glasses containing WO3 exhibit a high density of more than 6.00 g/cm3 and performs the enhanced compaction with increment of Eu2O3 content. The average coordination number of oxygen surrounding Eu3+ is 6.000 and the average bond length between Eu3+ and oxygen is 2.3740 Å. Eu3+ in glass absorb photons in visible light and near infrared region. The strong reddish orange emission around 613 nm via 5D0→7F2 radiation transition of Eu3+ was generated under different types of excitation such as ultraviolet, visible light and X-ray. The Gd3+ - Eu3+ energy transfer has an important role for strong reddish orange emission under 275 nm excitation. The Judd-Ofelt (J-O) theory was used to predict the radiative properties for the Eu3+ ion emission levels. The decay curves of the 5D0 levels exhibit single exponential nature with a lifetime of millisecond order. The high stimulated emission cross-section and intense emission with 613 nm wavelength suggests that the present Eu-WGdB glasses could be useful for the solid-state laser, display devices and radiation detecting material applications.

Resonant electron impact excitation of highly charged Fe ions studied with a compact electron beam ion trap

AbstractWe present extreme ultraviolet spectra of 3s3p–3s3d transitions in Fe14+ observed with a compact electron beam ion trap. The contributions of indirect excitation via a metastable state and resonant excitation are studied by observing the electron energy dependence of the spectra for the energy range of 60–210 eV. The results indicate that the 3s3d 1D2 level is directly excited from the 3s2 ground state whereas the 3s3d 3D3 level has a large contribution of the indirect excitation via the 3s3p 3P2 metastable state. Comparisons with the theoretical excitation cross sections including MNn resonant excitations show good qualitative agreement with the experimental results for the electron energy dependent features.

Synthesis, crystal structure and luminescent properties of novel lanthanide complexes with CAPh type ligand diphenyl-N-benzoylamidophosphate and bidentate nitrogen donors

Herein we report the synthesis and investigations of the new lanthanide coordination compounds [LnL3bipy] (Ln1) and [LnL3phen] (Ln2) with carbacylamidophosphate type ligand diphenyl-N-benzoylamidophosphate (HL = [PhCONHPO(OPh)2]) and additional ligands 2,2′-bipyridine and 1,10-phenantroline. The obtained complexes were characterized by means of X-Ray, thermal gravimetric analysis, IR, 1H NMR, UV absorption spectroscopy and luminescence spectroscopy at 298 and 77 K. The X-ray diffraction analysis of Eu1 and Eu2 shows that the complexes crystalize in monoclinic crystal system, P 21/n space group. Efficient energy transfer from organic ligands after their excitation sensitizes the lanthanide interior emission from 5D0 or 5D4 levels of EuIII or TbIII respectively, leading to a strong metal-centered luminescence with decay time 1.5–2.0 ms. Intrinsic quantum yields (QLnLn) for europium complexes found to be equal 78 (Eu1) and 70% (Eu2). Overall QY equals 46 and 42% respectively.

Study of the Effect of Injection Currents on White Light Emission of Ce-Doped YAG Phosphor Powder Prepared by Microwave Combustion

The behaviors of yttrium aluminum garnet (YAG) phosphor powder doped by cerium (YAG:Ce3+) was studied. Here, the YAG:Ce3+ nanopowders have been synthesized using microwave combustion (MW) according to the formula, Y(3-0.04) Al5O12: 0.04Ce3+ to produce white light emitting diode (WLEDs) by conversion from blue indium gallium nitride light emitting diode (InGaN LED, 445 nm) chips; the whole process took only 20 min. Pure YAG phase was obtained after annealing at 1050 °C for 5 h with nonaggregated and spherical particles. Thermogravimetry and derivative thermogravimetry (TG/DTG), X-ray powder diffraction (XRPD), transmission electron microscope (TEM), photoluminescence (PL), electroluminescence (EL) emissions and standard CIE 1931 chromaticity diagrams have been used to characterize the samples. The highest WLEDs emission was achieved for the annealed YAG:Ce3+, together with proper color rendering index (CRI), and tunable correlated color temperature (CCT). Finally, we conclude that the decreasing EL intensity at increased injection current is caused by the thermal ionization from the 5d1 level to the conduction band.

Synthesis and luminescence properties of novel red-emitting Eu3+ ions doped silicate phosphors for photonic applications

In the present work, we report on luminescence properties of Eu3+ ions doped KBaScSi3O9 silicate phosphors (KBSS) synthesized by high temperature solid state reaction method and the prepared phosphor samples were characterized through XRD, FE-SEM, photoluminescence and decay spectral measurements. The XRD pattern confirmed that the KBSS host lattice exhibited a monoclinic crystal structure. Room temperature photoluminescence (PL) spectroscopic results reveal that, on Eu3+ ion doping in the KBSS host matrix, the magnetic dipole transition (5D0 → 7F1) at 593 nm responsible for orange light, dominates the red emission with respect to the electric dipole transition (5D0 → 7F2) at 611 nm. The Judd-Ofelt (JO) intensity parameters Ωλ (λ = 2 and 4) have been calculated from the emission spectra to understand the nature of ligand environment around the Eu3+ ions. The radiative parameters, such as transition probability (A), stimulated emission cross-section (σPE), radiative lifetime (τR) and branching ratios (βR) corresponding to the 5D0→7F0, 5D0→7F1, 5D0→7F2, 5D0→7F3 and 5D0→7F4 emission transitions have been determined by using JO parameters and the refractive indices respectively. The concentration quenching effect for Eu3+ was found at the optimum doping concentration of 7 mol %. The CIE chromaticity coordinates were calculated from the luminescence spectra to explore the dominant emission colour of the title phosphors. The experimental lifetime values of 5D0 level of the Eu3+ doped silicate phosphors have been calculated and the obtained results were discussed in detail.

Kinetic properties of YAG: Eu3+ emission upon electron beam excitation

Luminescent properties of yttrium-aluminum garnet activated by different amount of europium (YAG:Eu3+) single crystals were studied by local cathodoluminescence (CL) technique. Samples were grown by flux method. CL spectra were obtained in the range from 400 to 800 nm with spectral resolution of 0.1 nm. The rise and decay kinetics of various CL bands were investigated. The concentration dependencies of CL intensity and decay times of transitions were plotted. The concentration quenching for 5D1-7F2 Eu3+ transition was observed at about 3.5 at.% of Eu by Y, and for 5D2-7F1 and 5D3-7F3 transitions – at about 2.5–3 at.% of Eu by Y. For transition 5D0-7F1 no concentration quenching was observed. The high-energy excitation capture efficiency by different energy levels of Eu3+ in YAG was estimated based on the dependence of the CL rise rate of these levels on the electron beam current density. It was found that 5D1 energy level excitation capture efficiency is about three times higher than that of the 5D0, 5D2 and 5D3 energy levels.

Sensitivity of a solid Eu(III) complex towards acetonitrile vapor: Structural and spectroscopic characterization

The Eu(III) nitrate complex of the meso- N,N′-bis(2-pyridylmethylene)-1,2-(R,S)-cyclohexanediamine ligand was synthesized and characterized by single crystal and powder X-ray diffraction. The crystal lattice of the complex is capable of absorbing and desorbing selectively acetonitrile molecules, at 293 K upon an acetonitrile vapor pressure of ∼0.1 × 105 Pa. This process, which is partially reversible, can be easily followed by both powder X-ray diffraction (P-XRD) and Eu(III) luminescence spectroscopy. The acetonitrile molecule, located in the outer coordination sphere of the metal ion, does not affect the radiative transition probability of 5D0 level of Eu(III) and also it does not activate further non-radiative channels from this level. On the other hand, this molecule is capable of affecting the energy position and intensities of the crystal field components of the 5D0→7F2 transition. The complex in solid form can be considered a promising material for the optical sensing of acetonitrile vapors.

Optical studies on Tb3+: Dy3+ singly and doubly doped Borosilicate glasses for white light and solid state lighting applications

Host (H), Singly and co-doped Dy3+/Tb3+ ions borosilicate glasses (S1-S7) were fabricated by a traditional melt-quenching-annealing method to investigate their luminescence properties as well as their suitability for the development of SSL (solid-state lighting) and W-LEDs (white light-emitting diodes). The X-ray diffraction profile indicates the amorphous structure nature of the prepared glasses. The J-O (Judd-Ofelt) intensity parameters Ωt(t=2,4,6) are evaluated for both singly Dy3+, Tb3+ doped glasses according to their absorption spectrum. The Ω2 parameter of Dy3+ ion has higher value which indicates a higher degree of Dy3+ covalency and the neighbour ligands while Tb3+ ion in a lower degree of covalency where its Ω2 has low value. Also the radiative parameters for both singly doped ions (S1 and S2) are computed like probability of transition (AT), branching ratio (βr) and radiative lifetime (τr) for different bands. Further, both singly doped glasses reflects good properties for lasing application where the 4F9/2 manifold of S1 (0.5 mol% Dy3+) has radiative lifetime (τr) value of 1376 µs and higher value of (AT:447.02 s−1) in addition to branching ration of (βr:61.5%) for the (4F9/2→9H13/2) transition (576 nm). At the same time, S2 (0.5 mol% Tb3+) glass show a higher lifetime (τr:3753) for 5D4 level and (AT: 92.94 s−1) while the branching ratio for 5D4→7F5 band at 546 nm wavelength is (βr: 34.9%). The radiative emission properties were investigated according to the Tb3+ concentration increments. The mutual energy transfer (ET) occurrence between both ions (Dy3+, Tb3+) is demonstrated through the varying of their emission intensities. Furthermore, The chromaticity (x,y) color coordinates were evaluated according to the emission spectra of aforementioned glasses under excitation of 368 nm and 348 nm were found to be located in the white light color region of the CIE chromaticity color diagram. Also, from color-coordinated the color correlated temperature (CCT) is computed were found to be at high values (>4000). Thus, the fabricated glasses are suggested as a useful luminescence material for solid-state lightening as well as cool white light applications.

Role of modifier ion radius in luminescence enhancement from 5D4 level of Tb3+ ion doped alkali-alumino-telluroborate glasses

Alkali-alumino-telluroborate glasses with the different network modifier elements were prepared by melt–quenching method. Absorption, excitation, luminescence spectra as well as decay curves of 5D4 level were measured at room temperature. A phonon side band of 7F6 → 5D4 transition has been obtained from the excitation spectra of Tb3+ ion. The role of modifier ion radius in luminescence enhancement from 5D4 level of Tb3+ ion was discussed in detail. In prepared glasses, multiphonon relaxation rate from 5D3 level to 5D4 is enhanced in the host glasses containing modifier ions with large radius. This is main reason leading to the enhancement of luminescence from 5D4 level of Tb3+ ion in alkali-alumino-telluroborate glasses under excitation at 350 nm. Additionally, the Judd-Ofelt theory was used to estimate the features of ligand field and radiative properties of Tb3+ ion. The calculated results have shown that the 5D4→7F5 transition has potential applications for laser action and optical amplifier.

JUDD-OFELT ANALYSIS OF Tb3+ AND UPCONVERSION STUDY IN Yb3+–Tb3+ CO-DOPED CALIBO GLASSES

We report on the study of the spectroscopic properties in Ytterbium-Terbium (Yb3+-Tb3+) co-doped calcium lithium borate (CaLiBO) glasses, with the study’s focus being on the upconversion process. Intensity parameters Ωλ for CaLiBO:Tb3+ are determined by the Judd-Ofelt method to be Ω2 = 15.5 × 10-20 cm2, Ω4 = 1.90 × 10-20 cm2 and Ω6 = 3.69 × 10-20 cm2. We have also obtained electric-dipole (and magnetic-dipole) radiative transition probabilities, branching ratios, and lifetime for the Tb3+:5D4 and 5D3 levels. In addition, an evaluation of the upconversion processes by luminescence and time-resolved spectroscopy were carried out. The upconversion rise and decay times, energy transfer probability from Yb3+ to Tb3+ ions, and the efficiency of the processes that depopulate the Tb3+:5D4 level after resonantly pumping the Yb3+:2F5/2 level were estimated. Our results showed that a cooperative energy transfer (CET) from two Yb3+ ions to one Tb3+ ion is the origin of the Tb3+ upconversion luminescence in the visible region. While, CET followed of the cross relaxation or/and excited state absorption is responsible for the upconversion luminescence in the ultraviolet region.

Multi-peaked broad-band red phosphor Y3Si6N11:Pr3+ for white LEDs and temperature sensing.

The indispensable broad-band red phosphors for LED lighting generally show a long emission tail for wavelengths longer than 650 nm, which consumes excitation energy but contributes little luminance. Here, we report, for the first time, a broad red emission band with a steep falling edge at 652 nm, formed of widely distributed 1D2 → 3H4 emission lines of Pr3+ in Y3Si6N11 due to a large Stark splitting of the 3H4 (930 cm-1) and 1D2 (725 cm-1) levels. The red emission exhibits a 43 nm bandwidth, which is the widest in Pr3+-doped phosphors reported so far. The red Y3Si6N11:Pr3+ phosphor was applied for the fabrication of 310 nm UV chip-based white LEDs, and a high color rendering index of 96 at a low correlated color temperature of 4188 K was achieved. Furthermore, a temperature-sensing scheme was proposed based on the temperature-dependent intensity ratios of the emission lines from the thermally coupled and large Stark splitting levels of the 1D2 state. Relative sensitivities as a function of temperature were studied in the range of 93-473 K. The findings of this study indicate that Y3Si6N11:Pr3+ is an attractive broad-band red phosphor for both high color rendering white LEDs and temperature sensing applications.

Structural and electronic properties of NaTaO3 cubic nanowires.

Sodium tantalate nanostructures have been classified among the best materials to conduct photocatalytic reactions. Therefore, understanding the relationship between nanoscale surface phenomena and photocatalytic properties is of fundamental importance. We performed Density Functional Theory calculations to investigate how chemically different facets may affect intrinsic properties of NaTaO3 cubic nanowires. Besides half-metallicity, the NaO-terminated wire relaxes structurally, presenting unoccupied down O 2p levels located above its valence band due to severely reduced coordination of its edges, which may allow it to be applied in spintronics systems. NaTaO-terminated wires have surface TaO4 units that, upon structural reconstruction, become more planar and introduce occupied Ta 5d levels below their conduction band. The emergence of such levels is also related to the overlap of Ta dz2 orbitals from adjacent NaTaO facets. Amongst other properties discussed herein, localized levels may be relevant for photocatalysis not only in terms of intrinsic bandgap engineering but also concerning the alignment with water redox potentials.

Thermally stable Ca2Ga2SiO7:Tb3+ green emitting phosphor for tricolor w-LEDs application

A series of Tb3+ doped Ca2Ga2SiO7 were successfully prepared by conventional solid-state reaction technique and characterized via X-ray diffraction (XRD), photoluminescence excitation and emission spectra, and luminescent decay curve. XRD analysis revealed the presence of a single phase tetrahedral structure of Ca2Ga2SiO7 belonging to P4¯21 m space group. The emission spectra revealed peaks arising from both 5D3 and 5D4 level under the most intense excitation of 374 nm, and the emission color varied from blue to green via greenish-yellow by altering the Tb3+ concentrations. The energy transfer interaction between Tb3+ ions was dipole-dipole in nature, as evident from the Dexter theory and Inokuti- Hirayama model. The emission intensity remained at 95.28 % and 86.30 % of the initial value at 398 K and 498 K for the optimized sample, respectively indicating strong thermal stability. The results mentioned above indicated that Tb3+ doped thermally stable Ca2Ga2SiO7 has potential application in the w-LEDs.

Spectroscopic properties of thulium doped (Lu0.25Gd0.75)2SiO5 (LGSO) single crystals

In this work, spectroscopic properties of (Lu0.25Gd0.75)2(1-x)Tm2xSiO5 (x = 0.04 and 0.005) single crystals were investigated. The material was found to be biaxial, exhibiting strong optical anisotropy, as clearly demonstrated in polarized absorption and emission spectra. Data from room temperature polarized absorption spectra were used in calculations within the phenomenological Judd-Ofelt model. The intensity parameters Ωt were established at Ω2 = 3.24 (±0.58), Ω4 = 2.96 (±0.24) and Ω6 = 0.86 (±0.14) [10−20 cm2]. The values of fluorescence lifetimes of the 1D2 and 1G4 levels were measured and subsequently compared with those calculated using the Judd-Ofelt theory. The strong absorption bands located at wavelengths around 355, 460 and 790 nm, related to the 3H6 → 1D2, 1G4, 3H4 transitions, were found suitable for optical pumping of the investigated material. The characteristics of emission spectra recorded in the blue (ca. 455 nm) and IR (ca. 1750 nm) regions indicate that further investigations of stimulated emission within those wavelength ranges are well justified and can be considered promising.

Energy transfer investigation of Sm3+/Eu3+ CaBAl glasses

Sm3+/Eu3+ codoped CaBAl glasses were prepared by conventional melt-quenching method, and their structural and optical properties were studied. The values of volumetric density and electronic polarizability showed an increase with the addition of Sm2O3. The Fourier-transform infrared spectroscopy (FTIR) spectra indicated the existence of trigonal and tetrahedral borate groups. The N4 values revealed that Sm2O3/Eu2O3 codoping favored the conversion of structural units from BO4 to BO3. The observed absorption bands in UV/VIS spectra were attributed to Eu3+ and Sm3+ transitions, from the ground states 7F0 and 6H5/2 to the various excited states. Color coordinates at CIE diagram were studied for the codoped glasses upon exciting at 405 nm. The energy transfer from the level 4G5/2 of Sm3+ to the 5D0 level of Eu3+ was verified by means of the luminescence results. With the addition of Sm3+, emission intensity of Eu3+ has been enhanced due to migration of Sm3+ excitation energy. The mechanism for energy transfer from Sm3+ to Eu3+ was investigated by Dexter energy transfer formula and Reisfeld's theory application on photoluminescence decay curves. A decrease in the lifetime of 4G5/2 → 6H7/2 transition was observed when Sm3+ was increased, probably due to ion-ion interaction and excitation energy migration.

Study on the structure and luminescence quenching of Pr doped Na0.5Bi4.5Ti4O15 multifunctional ceramics

In this work, Pr doped Na0.5Bi4.5Ti4O15 ceramics are prepared via conventional solid reaction method. We particularly here report that the emission spectra under 451 nm excitation is dominated by green emission from 3P0,1 level over red emission from 1D2 level. The emission from 3P0,1 level is more subject to non-radiative relaxation than that from 1D2 level, however, the emission from 1D2 level is more strongly affected by concentration quenching than that from 3P0,1 level. Besides, oxygen vacancy-related luminescence quenching is also observed.

Investigation of binding tendency of Eu(III) and La(III)-Schiff base complexes to selected oxy-anions and amino acids

New Eu(III) and La(III)/Schiff base complexes have been synthesized and fully characterized from the Schiff base ligand: L, (E)-N′-(pyridin-2-ylmethylene)acetohydrazide. The simple tri-aqua complex: [EuL2(H2O)3]Cl3 (EuL) emits intense red luminescence from the 5D0 level of Eu(III). The binding tendency of EuL and LaL, was investigated in solution for oxy-anions such as acetate, perchlorate, sulphate, nitrate, carbonates, ethyl phosphonate, as well as some selected amino acids (AA) such as l-alanine (Ala), l-cysteine (Cys) and l-leucine (Leu). The anion selectivity is based on the anionic size and the coordination mode as bidentate chelaters. The ESI-MS confirmed the formation of 1:1 EuL-AA or EuL-oxy-anion chelates in solution. These chelates are responsible for the luminescence quenching from Eu(III). The amino acids exhibit smaller binding constants to EuL (log K = 4.08–4.98 M−1) than the oxy-anions (log K = 4.65–6.54 M−1), but they maintain longer luminescence lifetime from Eu(III) (0.45–0.51 ms). This work suggests that luminescence lifetime measurements of EuL may be useful in distinguishing between different types of substrates in solution.

Various strategies for optical thermometry with high sensitivities based on rare earth ions doped BaY2Si3O10 phosphors

To develop new temperature-sensing phosphors, the Eu2+, Ce3+-Tb3+ and Yb3+-Tb3+ doped BaY2Si3O10 (BYSO) samples were designed. Both downshifting and upconversion (UC) luminescence properties were evaluated. In Eu2+-activated BYSO, asymmetric emission bands appear upon 350 nm excitation due to more than one Eu2+ emission center. For the different Eu2+ centers, their fluorescent intensity ratio (FIR) exhibits a linear relationship with temperature. High sensitivities for optical thermometer were achieved. In Ce3+-Tb3+ codoped BYSO, an efficient energy transfer from Ce3+ to Tb3+ was observed by exciting at 330 nm. The FIR for Ce3+ and Tb3+ emissions shows a continuous decrease with increasing temperature, and the corresponding sensitivities were evaluated. In Yb3+-Tb3+ codoped BYSO under 980 nm excitation, the intensity of Tb3+ emission from 5D3 level shows a faster decrease rate than that from 5D4 level with rising temperature. Their FIR with temperature was studied for optical thermometry, where very high sensitivities were obtained.