Broad Charge Transfer Band Research Articles

Phosphorus(V) Tetraazaporphyrin with an Intense, Broad CT Band in the Near-IR Region.

In phosphorus tetraazaporphyrins (PTAPs), the Q- and charge-transfer (CT) bands appear as a result of configuration interaction between their excited states. On the basis of this concept, a PTAP with an intense, broad CT band in the near-IR region has been rationally designed and realized by introducing eight diphenylaminophenyl (dPAP) groups. The order of the CT and Q-bands in ascending energy was supported by magnetic circular dichroism (MCD) spectroscopy and theoretical calculations. An intense two-photon absorption was also found in the deep near-IR region.

Luminescence investigations of hydrothermally synthesized terbium doped zirconium tungstate nanorods

Rare-earth based phosphors play a key role in enhancing the quality of the phosphor converted LEDs (pc-LEDs). But the creation of phosphors with high thermal stability is still a task. This work aims to investigate the luminescence properties of ZrW2O8, which is known to have a negative or almost zero coefficient of thermal expansion. ZrW2O8 doped with Tb3+ is optimized by the conventional hydrothermal method in acidic medium. The PXRD analysis confirms the crystallization of the material into high purity cubic phase to the P213 space group. The tungstate group's distinctive vibrational modes were identified by FTIR analysis. TGA analysis demonstrates the remarkable thermal stability of the material over a wide temperature range. The preferential growth along one direction to form distinct nanorods was investigated using TEM. The optical band gap is found to increase after doping. The high and broad charge transfer band at 284 nm in the excitation spectra is an indication of the efficient energy transfer from the host to Tb3+ ions and the possibility of NUV excitation. The characteristic green emission peak of the Tb3+ at 543 nm and the values of the CCT and CP obtained using the colorimetry study suggest that the obtained material can be used as a green component to produce cold white LEDs.

Study of photoluminescence behaviors and Judd-Ofelt analysis of Eu3+ doped double perovskite Ba2GdSbO6 phosphor for highly pure and strong red-light generation

An array of Eu3+ doped Ba2GdSbO6 luminescent materials have been synthesized by the conventional solid-state (high temperature) reaction route. Surface morphology has been studied via Field Emission Scanning Electron Microscopy. The structural and optical behaviors have been studied using X-Ray Diffraction (XRD), FTIR, Raman spectroscopy, Diffuse reflectance spectroscopy, Photoluminescence excitation (PLE), and Photoluminescence emission (PL) spectra. FTIR and Raman's spectra provided the chemical functional group and different vibrational levels within the samples. The calculated optical band gap was 4.40 eV and 4.47eV for pure and optimized samples respectively. Photoluminescence emission curves have been recorded for 245 nm of excitation wavelength and the highest emission peak was focused at 595 nm corresponding to 5D0 → 7F1. Similarly, the Photoluminescence excitation curves were monitored at the emission wavelength of 595 nm and a broad charge transfer band (CTB) was observed from 230 to 285 nm. The emission spectra show the concentration quenching effect beyond the 2 mol% Eu3+ concentration. The corresponding transitions of Eu3+ were further utilized to obtain the Judd-Ofelt (J-O) transition intensity parameters Ωλ (λ = 2, 4) for each sample. Additionally, by studying decay kinetics, the average lifetime of the red emission of the samples has been evaluated, which was 4.622 ms. The photometric study also reveals the CIE coordinates, color purity and CCT values of the proposed phosphor material. Thus, the results obtained from these characterizations, suggest that the prepared sample may behave as a potential candidate in the case of UV-excited red light-emitting phosphor material for light-emitting diodes and field emission devices.

Asymmetrically Coordinated Heterodimetallic Ir–Ru System: Synthesis, Computational, and Anticancer Aspects

Herein, we present an unprecedented formation of a heterodinuclear complex [{(ppy)2IrIII}(μ-phpy){RuII(tpy)}](ClO4)2 {[1](ClO4)2} using terpyridyl/phenylpyridine as ancillary ligands and asymmetric phpy as a bridging ligand. The asymmetric binding mode (N∧N-∩-N∧N∧C-) of the phpy ligand in {[1](ClO4)2} is confirmed by 1H, 13C, 1H-1H correlated spectroscopy (COSY), high-resolution mass spectrum (HRMS), single-crystal X-ray crystallography techniques, and solution conductivity measurements. Theoretical investigation suggests that the highest occupied molecular orbital (HOMO) and the least unoccupied molecular orbital (LUMO) of [1]2+ are located on iridium/ppy and phpy, respectively. The complex displays a broad low energy charge transfer (CT) band within 450-575 nm. The time-dependent density functional theory (TDDFT) analysis suggests this as a mixture of metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT), where both ruthenium, iridium, and ligands are involved. Complex {[1](ClO4)2} exhibits RuIIIrIII/RuIIIIrIII- and RuIIIIrIII/RuIIIIrIV-based oxidative couples at 0.83 and 1.39 V, respectively. The complex shows anticancer activity and selectivity toward human breast cancer cells (IC50; MCF-7: 9.3 ± 1.2 μM, and MDA-MB-231: 8.6 ± 1.2 μM) over normal breast cells (MCF 10A: IC50 ≈ 21 ± 1.3 μM). The Western blot analysis and fluorescence microscopy images suggest that combined apoptosis and autophagy are responsible for cancer cell death.

Synthesis of Liquid crystals with terminal polar groups and study their mesomorphic and spectroscopic properties

Synthesis new Schiffs bases substituted with polar groups CI . Br , F , N02, CH3 , OCH3 , COCH3 in para position or aniline moiety, and derived Cu ( II ) complex from the Schiff base which substituted with COCH3. The Schiffs bases substituent with CH3 , OCH3 exhibited Nematic phase but the other Schiff bases and Cu ( II ) complex exhibited Smectic phase ( Sc ) only. Molecular complexes of Cu (II) complex
 with various nitrogen bases were studied spectrophotometrically in benzene solvent at
 different temperatures. These entire complex show a new broad charge transfer band in the visible region of the electromagnetic spectrum.
 All the donors are known to form I: I complex with the acceptor and their
 stoichiometry was unaffected by the variation of temperature over a small interval. The thermodynamic and spectroscopic parameters were evaluated. The order of donor strength followed the sequence: 
 Butyl amine> 4 - methyl pyridine > N,N –
 dimethyl aniline.

Exploring the potential of Eu3+ and Mn4+ activated LaAlO3 phosphors as red and far-red emitters for horticulture lighting.

The development of efficient red and far-red emitters, for efficient plant absorption in the Photosynthetically Active Radiation (PAR) region, holds significance in contemporary plant growth control. This study focuses on the synthesis and characterization of LaAlO3 as a host material, doped with Eu3+ and Mn4+ ions, using a solid-state reaction method. The investigation encompasses the creation and analysis of both single-doped and co-doped samples, employing techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. XRD analysis consistently confirmed the perovskite-like structure of all samples, devoid of detectable impurities or major structural changes due to doping. SEM images revealed a uniform distribution of regularly shaped particles for the co-doped sample. The PL spectroscopy showed that the doping led to strong photoluminescence, with the co-doped sample exhibiting the intensity of each of the ions independently neither exhibiting quenching nor energy transfer mechanisms. The excitation spectrum of Eu3+ exhibited a broad charge transfer band at approximately 328 nm, coupled with characteristic f-f excitation bands. On the other hand, the Mn4+ ion's excitation spectrum featured transitions from ground state (4A2g) electrons excited to higher excited states (4T1g, 2T2g, and 4T2g) centered at 350 nm and within the region 250-550 nm. The co-doped sample was excited at a common excitation wavelength of 460 nm and underwent an in-depth examination of its photoluminescent properties, including decay curves analysis and time dependence also. The results from this study suggest that the synthesized phosphor materials exhibit substantial potential for diverse applications, including but not limited to solid-state lighting for efficient plant growth.

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.

C–H⋯S Hydrogen Bond Assisted Supramolecular Encapsulation of Fullerenes with Nanobelts

C–H⋯S Hydrogen Bond Assisted Supramolecular Encapsulation of Fullerenes with Nanobelts

Photoluminescence of β-Ba2ScAlO5: Eu3+ red emitting phosphors effectively activated by UV light

Increasing the absorption capacity of trivalent rare-earth metal ions doped phosphors excited by ultraviolet (UV) light is a hot topic. Herein, a novel β-Ba2ScAlO5:Eu3+ red-emitting phosphor with strong absorption in the UV region was reported. The photoluminescence spectra show that β-Ba2ScAlO5:Eu3+ phosphor exhibited a broad charge transfer band ranging from 220 nm to 350 nm, and it can transfer the excited electrons to Eu3+ ions. A strong red emission peak of Eu3+ ions centered at 613 nm (5D0 → 7F2 transition) was observed under 300 nm excitation. The Judd-Ofelt intensity parameters Ω2 and Ω4 were calculated as 1.37 × 10−20 cm−2 and 0.14 × 10−20 cm−2, which indicates a higher asymmetry environment around Eu3+ ions. All experimental results suggest that β-Ba2ScAlO5: Eu3+ materials as red phosphors own potential for application in light-emitting diodes and optical temperature sensors.

Synthesis and characterization of wide band excited yellow phosphor LaNb2VO9:Dy3+ and application in potential fingerprint and lip print detection

LaNb2VO9:Dy3+ yellow phosphors were synthesized by high-temperature solid-state method. The luminescent properties, structure, and color purity of the products were studied systematically. LaNb2VO9:Dy3+ phosphors can be effectively excited by two broad charge transfer bands (CTB) under 307 nm excitation. The strong yellow light at 570 nm was caused by the 4F9/2 → 6H13/2 energy level transition of Dy3+. The optimum doping concentration of LaNb2VO9:xDy3+ phosphor was x = 0.10 mol, and the dominant factor of concentration quenching effect is the nearest-neighbor ions interaction. The chromaticity coordinates of International Committee LaNb2VO9:Dy3+ were located in the yellow color area. In addition, LaNb2VO9:0.1Dy3+ phosphor can well visualize the latent fingerprint (LFP) image and lip print image. The levels 1–3 features of fingerprint and groove pattern of lip print can be easily recognized, with high resolution and contrast. The experimental results showed LaNb2VO9:Dy3+ can be well applied to LFP and lip print detection.

Synthesis, Optical Properties, and Electrochemical Behavior of 5,10,15,20-Tetraaryl-5,15-diazaporphyrin-Amine Hybrids.

This work reports a series of covalently linked hybrids comprising 5,10,15,20-tetraaryl-5,15-diazaporphyrinoids (M-TADAP; M = Ni, Zn, Cu) and amines. M-TADAP-amine hybrids were prepared via the metal-templated cyclization of the corresponding metal(II)-dipyrrin complexes and redox reactions on the DAP unit. In the UV/vis/near-IR absorption spectra of the hybrids containing an 18π-electron DAP ring, broad charge-transfer bands were observed, reflecting the electron-donating property of the para-aminophenyl groups and the electron-accepting property of the 18π TADAP dication. The electrochemical behavior of the M-TADAP-amine hybrids was strongly dependent on the structure of the peripheral amine units. Further electrochemical oxidation of the hybrids bearing N-Ph groups conceivably generated amine-centered radicals, which sequentially underwent irreversible coupling to form benzidine-linked M-TADAP polymer films. The Ni-TADAP-benzidine polymer exhibited the electric conductivity of 1×10-3 S m-1 .

Preparation and luminescence properties of ZnWO4 :Eu3+ ,Tb3+ phosphors.

A series of ZnWO4 :Eu3+ ,Tb3+ phosphors was prepared using a co-precipitation method at room temperature. The structures and luminescence properties of the materials were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and UV-vis light, differential thermal analysis-thermogravimetric analysis, fluorescence spectra and the calculated Commission Internationale de l'Éclairage (CIE) coordinates. The results showed that the material had a monoclinic structure and the P2/c group was determined using XRD. FTIR spectroscopy confirmed the existence of W-O, Zn-O bonds, and Zn-O-W groups in WO6 and ZnO6 octahedra. In the excitation spectrum, there was an overlap of the broad band charge transfer bands belonging to O2- →W6+ and O2- →Eu3+ or O2- →Tb3+ transitions in the range 200-325 nm, and excitation bands between 350 and 500 nm belonged to the characteristic absorption bands for Eu3+ and Tb3+ . Therefore, the phosphor can be used as a single component tunable phosphor in light-emitting diodes.

High purity blue photoluminescence in thulium activated α-Na3Y(VO4)2 nanocrystals via host sensitization

A novel blue emitting glaserite type α-Na3Y(VO4)2 nanocrystals substituted with the trivalent thulium ions were synthesized for the first time via citrate based solution combustion method. The monoclinic structure and well dispersed spherical morphology of the synthesized nanocrystals were confirmed by XRD, TEM, HRTEM and SAED analysis. Host lattice emits broad band blue color and it originates from the VO43−. The presence of a very intense and broad charge transfer band in excitation spectra of α-Na3Y(VO4)2:Tm3+ monitored under 474 nm demonstrates the efficient energy transfer from VO43− to Tm3+ in α-Na3Y(VO4)2:Tm3+. Photoluminescence studies of Tm3+ activated α-Na3Y(VO4)2 samples show blue emission under excitation wavelength 310 nm. The optimal doping concentration of Tm3+ ions in α-Na3Y(VO4)2 phosphors is found to be around 1.5 mol % and the major mechanism for concentration quenching is the dipole - dipole interaction. The quantum yield for the sample with optimum concentration is measured to be 18.16%. The CIE chromaticity color coordinates were calculated and it is very much closer to the NTSC standards with high color purity. The lifetime of the thulium characteristic blue emission is found to be in the order of 0.1 ms. All the results clearly indicate that pure α-Na3Y(VO4)2 as well as rare earth Tm3+ activated α-Na3Y(VO4)2 nanocrystals can be used as potential candidates in the field of optoelectronics, especially for the fabrication of near-UV based white LEDs, bio-imaging and labeling etc.

Unusual dual-emissive heteroleptic iridium complexes incorporating TADF cyclometalating ligands.

Five new neutral heteroleptic iridium(iii) complexes IrL2(pic) (2-6) based on the archetypical blue emitter FIrpic have been synthesised. The cyclometallating ligands L are derived from 2-(2,6-F2-3-pyridyl)-4-mesitylpyridine (7), 2-(3-cyano-2,6-F2-phenyl)-4-mesitylpyridine (8), 2-(2,6-F2-phenyl)-4-[2,7-(HexO)2-9H-carbazol-9-yl]pyridine (9), 2-(2,6-F2-3-pyridyl)-4-[2,7-(HexO)2-9H-carbazol-9-yl]pyridine (10) and 2-(3-cyano-2,6-F2-phenyl)-4-[2,7-(HexO)2-9H-carbazol-9-yl]pyridine (11) for complexes 2, 3, 4, 5 and 6, respectively. The carbazole-functionalised ligands 9-11 show weak thermally activated delayed fluorescence (TADF) in solution. Complexes 5 and 6 reveal dual emission in polar solvents. A broad charge transfer (CT) band appears and increases in intensity relative to the higher energy emission band as solvent polarity is increased. The dual emission occurs when the energy of the ligand 3CT state is comparable to that of the 3MLCT state of the complex, resulting in fast interconversion between the two. Assignment of the ligand TADF and dual emission properties is supported by hybrid density functional theory (DFT) and time dependent DFT (TD-DFT) calculations. Phosphorescent organic light emitting devices (PhOLEDs) have been fabricated using these complexes as sky-blue emitters, and their performance is compared to devices using FIrpic and the previously reported complex IrL2(pic) 1 (L from the 2-(2,6-F2-phenyl)-4-mesitylpyridine ligand). For identical device structures, the device containing the carbazole complex 4 performs best out of the seven complexes. The dual emission observed in solution for complexes 5 and 6 is not observed in their devices.

Impact of Eu3+ concentration on the fluorescence properties of the LiGd(W0.5Mo0.5O4)2 novel red phosphors

Novel red emitting Eu3+ (y = 0.0–1.0) activated LiGd1-y(W0.5Mo05O4)2 phosphors were synthesized via polymeric complex sol-gel method. Powder X-ray diffraction (XRD) results and scanning electron microscope (SEM) micrographs of the phosphors reveal tetragonal crystalline structure and irregular sphere-like morphology for the particles with average size of 1–3 μm. Broad charge transfer band (CTB) in UV region and bright red emission for the electric dipole 5D0 → 7F2 transition at 615 nm was observed for Eu3+ activated tungsto-molybdate phosphors from the fluorescence excitation and emission results. These phosphors promote strong energy transfer from the (MoO4)2-/(WO4)2- groups to Eu3+ ions and lead to the strong enhancement in the intensity of red emission under 395 nm (near UV) excitation. Effect of Eu3+ activator concentration on the luminescence nature of the tungsto-molybdate solid solution and the critical concentration of activator Eu3+ for maximum red emission were investigated. Asymmetric ratio and the critical distance between the Eu3+ activator were calculated and decay scheme for the phosphors were determined. The conditions for intense red emission of the LiGd(W0·5Mo0·5O4)2:Eu3+ phosphors were optimized.

Novel orange–red emitting phosphor Ba2ScNbO6:Eu3+ for WLEDs: synthesis and luminescence properties

A novel perovskite type orange–red emitting phosphor Ba2ScNbO6:xEu3+ (BSN:xEu3+) was designed and synthesized by solid-state route. The X-ray diffraction, luminescent properties, fluorescent decay times and thermal stability were utilized to characterize the as-prepared samples. The X-ray diffraction confirmed BSN:xEu3+ had a cubic structure with the space group of Pm-3m (221). Photoluminescence (PL) excitation spectra consisted of a broad charge-transfer band and the f–f transition of Eu3+ ions in the violet and blue wavelength regions. The PL spectra displayed orange–red emitting luminescence with the strongest 5D0 → 7F1 transition at 595 nm. The mechanism of energy transfer between Eu3+ ions in BSN has been confirmed to be resonant type via dipole–dipole interaction. Besides, BSN:xEu3+ phosphors exhibit distinct thermal quenching properties, whose emission intensity at 423 K still exceed 71% of the initial value at room temperature. And the CIE coordinate of BSN:0.18Eu3+ phosphor is closed to the Nichia Corporation developed Amber LED NSPAR70BS. All results indicate that BSN:xEu3+ could be a promising phosphors for near-ultraviolet-based white light-emitting diodes.

Enhancement of near-infrared up-conversion and blue down-conversion luminescence in LuNbO4 :Yb3+ ,Tm3+ with Ga3+ and Ta5+ substitutions.

Under a 980-nm excitation, the up-conversion (UC) spectra of LuNbO4 :Yb3+ ,Tm3+ powders exhibited predominantly near-infrared bands (~805nm) of Tm3+ through an energy transfer process from Yb3+ to Tm3+ . Regarding the down-conversion (DC) luminescence of the powders, the photoluminescence excitation spectra consisted of a broad charge transfer band (270nm) due to [NbO4 ]3- and sharp band (360nm) of Tm3+ , while the corresponding emission spectra exhibited a blue emission at 458nm. Upon substitution of Ga3+ and Ta5+ for Lu3+ and Nb5+ , respectively, both UC and DC luminescence properties were significantly enhanced. For the Ga3+ substitution, the increased emission intensity could be explained by the crystal field asymmetry surrounding the Tm3+ ions induced by the large difference in ionic radius between Ga3+ and Lu3+ . For the Ta5+ substitution, we believe that an M'-LuTaO4 substructure was formed in the host, which led to the formation of a TaO6 octahedral coordination instead of a NbO4 tetrahedral coordination. Consequently, the crystal symmetry of the local structure was modified, and thus the UC and DC luminescence properties were enhanced. The dual-mode (UC and DC) luminescence demonstrates that LuNbO4 :Yb3+ ,Tm3+ has a great potential in the fields of temperature sensing probes, anti-counterfeiting, and bioapplications.

Sm3+ doped tetragonal lanthanum molybdate: A novel host sensitized reddish orange emitting nanophosphor

Abstract A series of trivalent samarium doped lanthanum molybdate nanophosphors were prepared by co-precipitation route. The formation of highly crystalline tetragonal nanocrystals with space group I41/a is identified from powder X-ray diffractogram. The morphology and the oriented attachment mediated growth mechanism of the nanocrystals were recognized from TEM analysis. The strong and broad charge transfer band in the near ultra violet region favours excellent excitation of the nanophosphors and the energy transfer from host matrix to Sm3+ ions is established on account of the characteristic emissions of trivalent samarium ions upon host sensitization. The Judd-Ofelt (JO) theoretical analysis was carried out to have an insight into the spectroscopic characteristics of La2-xSmx(MoO4)3 nanophosphors. The relatively higher value of Ω2 predicts more asymmetric environment of Sm3+ sites in the host lattice, favouring the dominance of electric dipole transitions and the various radiative parameters are evaluated. In spite of the excitation channel, the 4G5/2 → 6H9/2 transition of Sm3+ observed at 645 nm is the most prominent emission transition. The maximum emission intensity is observed for La1.98Sm0.02(MoO4)3 nanophosphors and as the doping concentration exceeds this limit, there will be fall in emission intensity due to concentration quenching effect. A detailed investigation on the decay behaviour of host sensitized and direct excited emission of samarium ions was conducted and the average lifetime values are calculated. The CIE chromaticity co-ordinates calculated for different excitation routes fall in the reddish orange region of CIE diagram and the same for La1.98Sm0.02(MoO4)3 nanophosphors are found to be (0.601, 0.394) with a colour purity of 97.21% which disclosed the relevance of La2−xSmx (MoO4)3 as a potential red phosphor material.

Synthesis and Photoluminescence Properties of BaWO4:RE3+ (RE = Eu or Sm) Phosphors

BaWO4:RE3+ (RE = Eu or Sm) phosphor powders were prepared with different doping concentrations of the activator ion by using the conventional solid-state reaction method. The dependences in the crystal structure, luminescence intensity, and morphology on the Eu3+ and the Sm3+ concentrations in BaWO4 were investigated using X-ray diffraction (XRD), photoluminescence spectrophotometry, and scanning electron microscopy (SEM), respectively. XRD analysis showed tetragonal BaWO4 structures for all the phosphors synthesized, regardless of the type and the doping concentration of the activator ion. SEM images indicated that as the concentration of activator ions was increased, the crystalline particles showed an increasing tendency to agglomerate irregularly. The room temperature excitation spectra of Eu3+- or Sm3+-doped BaWO4 phosphors consisted of a broad charge transfer band in the ultraviolet region and several sharp 4f-4f transitions. When Eu3+-doped BaWO4 phosphors were excited at 274 nm, the emission spectra exhibited sharp bands due to inner shell transitions occurring from the excited energy state 5D0 to the lower energy levels 7F J (J = 1, 2, 3, and 4). For Sm3+-doped BaWO4 phosphors, three intense emission peaks at 568, 603, and 649 nm and a very weak line at 712 nm were observed. The highest asymmetry ratio-the intensity ratio of the 4G5/2 → 6H9/2 electric dipole to the 4G5/2 → 6H5/2 magnetic dipole transitions-was obtained for 1 mol% doping of Sm3+, indicating that the Sm3+ ions occupied the non-inversion symmetry sites.

Structural and photoluminescence characteristics of Sm3+ activated RE2Ti2O7 (RE = Gd, La) as orange-red emitting phosphors

A series of solid solutions with the general formula (Gd1−xSmx)2Ti2O7 (0 ≤ x ≤ 1) and (La1−xSmx)2Ti2O7 (x = 0 and 0.5) were prepared by traditional solid state method at 1200°C under air atmosphere. The X-ray powder diffraction, scanning electron microscopy (SEM) and Raman spectroscopy analysis were performed to confirm the phase purity and to characterize the structure of the as-synthesized materials. Rietveld refinement of XRD showed that (Gd1−xSmx)2Ti2O7 solid solutions crystallize in the pyrochlore structure (Fd3m, Z = 8) while (La1−xSmx)2Ti2O7 (x = 0 and 0.5) oxides adopt the layered-perovskite one (P21, Z = 4). The photoluminescence excitation, the emission spectra and the concentration effect were investigated. The excitation spectra of the phosphors show a broad charge-transfer band in the short wavelength region and several sharp lines in the longer wavelength region originated from Sm3+, which indicates that these phosphors can be effectively excited by UV chips. The Gd1.20Sm0.80Ti2O7 phosphor exhibits the strongest emission among (Gd1−xSmx)2Ti2O7 (0 ≤ x ≤ 0.50) solid solutions after the excitation at 292nm and could be useful for developing new luminescent materials. On the basis of PL spectroscopy, it was inferred that the Sm3+ ion stabilizes at Gd3+ site with inversion symmetry in the first luminescent material Gd1.20Sm0.80Ti2O7, whereas most of Sm3+ ion occupies La3+ site without inversion symmetry in the second luminescent material LaSmTi2O7. The energy bands gap were also determined using UV–visible diffuse reflectance spectroscopy. Both Gd1.20Sm0.80Ti2O7 and LaSmTi2O7 phosphors show a strong orange-red emission in the visible range, which may be useful for display technologies and LED applications.