Red emitting MTiO3 (M = Ca or Sr) phosphors doped with Eu3+ or Pr3+ with some cations as co-dopants

Ca (or Sr)TiO₃:Eu³⁺, M (Li⁺ or Na⁺ or K⁺) and CaTiO₃:Pr³⁺, M (Li⁺ or Na⁺ or Ag⁺ or K⁺ or Gd³⁺ or La³⁺) powders were prepared by combustion synthesis method and the samples were further heated to ～1000 °C to improve the crystallinity. The structure and morphology of materials were examined by X-ray diffraction (XRD) and a scanning electron microscopy (SEM). The morphologies of SrTiO₃:Eu³⁺, CaTiO₃:Eu³⁺ or CaTiO₃:Pr³⁺ powders co-doped with other metal ions were very similar. Small and coagulated particles of nearly cubical shapes with small size distribution having smooth and regular surface were formed. Photo-luminescence spectra of CaTiO₃:Pr³⁺ and co-doped either with Li⁺, Na⁺, K⁺, Ag⁺, La³⁺ or Gd³⁺ ions showed red emissions at 613 nm due to the ¹D₂ → ³H₄ transition of Pr³⁺. The variation of intensity of emission peak with different co-doping follows the order: K⁺ > Ag⁺ > Na⁺ > Li⁺ > La³⁺ > Gd³⁺. The characteristic emissions of CaTiO₃:Eu³⁺ lattices had strong emission at 614 and 620 nm for ⁵D₀ → ⁷F₂ with other weak transitions observed at 580, 592, 654, 705 nm for ⁵D₀ → ⁷F_n transitions where n = 0, 1, 3, 4 respectively in all host lattices. Photoluminescence intensity in SrTiO₃:Eu³⁺ is more than CaTiO₃:Eu³⁺ lattices. A remarkable increase of photoluminescence intensity (in ⁵D₀ → ⁷F₂ transition) was observed if co-doped with Li⁺ ions in CaTiO₃:Eu³⁺ and SrTiO3:Eu³⁺.     

Investigation on luminescence of Na3Ca6(PO4)5:Eu2+ phosphor for LEDs

In this paper, a series of Na₃Ca_6(1−x)(PO₄)₅:xEu²⁺ (NCP:xEu²⁺, 0 ≤ x ≤ 4%) phosphors were prepared by conventional solid-state reaction method, and their photoluminescence properties were studied. Upon 365 nm excitation, the typical NCP:2%Eu²⁺ phosphor shows an asymmetric bluish green emission band with the dominant peak at 498 nm which could be attributed to the 4f⁶5d¹-4f⁷ transition of Eu²⁺. By measuring the time-resolved photoluminescence spectra, it reveals more than one Eu²⁺ emission center in the Eu²⁺-activated NCP phosphors. By monitoring 498 nm, the excitation spectrum of NCP:2%Eu²⁺ demonstrates a broad excitation band ranging from 240 to 450 nm, which can match well with the emission wavelength of the NUV LED chip. The SEM image shows that the average particle size of NCP:2%Eu²⁺ is about 19.4 µm. The above results imply that the NCP:Eu²⁺ phosphor could have potential application in LEDs.     

Influences of substituting Na+ ions in Eu2+, Mn2+ doped Ba9Y2Si6O24 phosphors

Near-ultraviolet (NUV)-excitable phosphors composed of Ba_8.9-(1/2)pNa_pEu_0.1Y₂Si₆O₂₄ (p = 0–0.8) and Ba_8.7-qNa_0.4Eu_0.1Mn_qY₂Si₆O₂₄ (q = 0–0.4) were prepared via a solid-state reaction in a reducing atmosphere. The X-ray diffraction patterns of the obtained phosphors were examined to index the peak positions. After Na⁺ substitution for Ba²⁺ in the Ba_8.9Eu_0.1Y₂Si₆O₂₄ host lattice, the clear shift from green to yellow emission was observed. The Gaussian components of Ba_8.9-(1/2)pNa_pEu_0.1Y₂Si₆O₂₄ (p = 0, 0.4, and 0.8) phosphors were exploited by using the three different Eu²⁺ ion sites in the host lattice. The dependence of the luminescent intensity of the Mn²⁺ co-doped (q = 0–0.4) host lattices on the fixed Na⁺ and Eu²⁺ contents was also investigated. Co-doping Na⁺ with Mn²⁺ and Eu²⁺ emitters in the host structure enabled efficient energy transfer from Eu²⁺ to Mn²⁺. The mechanism underlying this energy transfer was also discussed. The Commission Internationale de I’Eclairage (CIE) coordinates near the yellow and red regions of the obtained phosphors were observed. Each of Ba_8.9Eu_0.1Y₂Si₆O₂₄, Ba_8.7Na_0.4Eu_0.1Y₂Si₆O₂₄, and Ba_8.6Na_0.4Eu_0.1Mn_0.1Y₂Si₆O₂₄ phosphors with a 405 nm LED chip was fabricated. The color rendering index (CRI, R_a) at correlated color temperature (CCT) with the CIE coordinates was exhibited for the LEDs. The thermal quenching and activation energy for the Ba_8.7Na_0.4Eu_0.1Y₂Si₆O₂₄ and Ba_8.6Na_0.4Eu_0.1Mn_0.1Y₂Si₆O₂₄ phosphors were measured.     

Single-phase Ce3+–Mn2+–Tb3+ tri–codoped barium–yttrium–silicate phosphors

Ce³⁺–Mn²⁺–Tb³⁺ cooperative barium–yttrium-orthosilicate phosphors composed of Ba_{9-3m/2-n-3p/2}Ce_mMn_nTb_pY₂Si₆O₂₄ (m = 0.005–0.4, n = 0–0.5, p = 0–0.5) were prepared using a solid-state reaction. The X-ray diffraction patterns of the resultant phosphors were examined to index the peak positions. The photoluminescence (PL) excitation and emission spectra of the Ce³⁺–Mn²⁺–Tb³⁺ activated phosphors were clearly monitored. The dependence of the luminescent intensity of the Mn²⁺–Tb³⁺ co-doped Ba_9-3m/2Ce_mY₂Si₆O₂₄ host lattices on Ce³⁺ content (m = 0.025, 0.1) was also investigated. Co-doping Mn²⁺ into the Ce³⁺–Tb³⁺ co-doped host structure enabled energy transfer from Ce³⁺ to Mn²⁺; this energy transfer mechanism is discussed. The phosphors of Ce³⁺–Mn²⁺–Tb³⁺ doped Ba₉Y₂Si₆O₂₄ host lattice were prepared for efficient white-light emission under NUV excitation. With these phosphors, the desired CIE values including white region of the emission spectra were achieved.     

Cooperative downconversion in Y3Al5O12 : RE3+,Yb3+ (RE = Tb,Tm, and Pr) nanophosphors

Abstract— Efficient near‐infrared (NIR) quantum cutting (QC) through cooperative downconversion in Y₃Al₅O₁₂ : RE³⁺,Yb³⁺ (RE = Tb, Tm, and Pr) nanophosphors has been demonstrated, which involves the conversion of the visible photon from RE³⁺ into the NIR emission of Yb³⁺ with the optimal quantum efficiency approaching 200%. The authors have analyzed the measured luminescence spectra and decay lifetimes and propose a mechanism to rationalize the NIR QC effect. The results indicate the potential of developing RE³⁺‐Yb³ dual‐ion‐based nanophosphors for the downconversion of high‐energy photons to multiple photons with an energy greater than the bandgap of silicon‐based‐photonics display devices.     

Spectroscopic and photoluminescence properties of MgO:Cr3+ nanosheets for WLEDs

This work explores the synthesis of nanocrystalline MgO:Cr³⁺ (1–9 mol%) nanophosphors via solution combustion route at 400 °C. The nanophosphors were well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra-Red (FTIR) spectroscopy. PXRD results confirm cubic phase and SEM micrographs indicate that the particles are highly porous and agglomerated. The TEM images show that the powder consists of spherical particles of size ∼5–15 nm. Upon 356 nm excitation the emission profile of MgO:Cr³⁺ exhibits an emission peak at 677 nm due to ²E_g → ⁴A_2g transition. It was observed that PL intensity increases with increase in Cr³⁺ concentration and highest PL intensity was observed for 3 mol% doped sample and afterward it decreases, attributed to concentration quenching. The resultant CIE chromaticity co-ordinates in the white region make the present phosphor highly useful for display applications and also for white light-emitting diodes (WLEDs).     

Synthesis of Sm3+ and Dy3+ doped LaBWO6 for evaluation as potential materials in luminescent display applications

A series of Sm³⁺ and Dy³⁺ doped LaBWO₆ phosphors were synthesized by high temperature solid state reaction. Recorded XRD patterns proved that the titled compound in a single phase has been obtained. Sm³⁺ and Dy³⁺ doped LaBWO₆ could emit orange and white light, respectively. The optimal doping concentration of Sm³⁺ or Dy³⁺ was experimentally ascertained to be 6 mol%. The critical distance of energy transfer for Sm³⁺ or Dy³⁺ doped sample is 1.540 nm. In addition, there is no cross energy transfer between the Sm³⁺ and Dy³⁺ ions in the co-doped samples. The results indicated that the electric dipole–dipole interaction is predominant energy transfer mechanism for concentration quenching of Sm³⁺ or Dy³⁺ doped LaBWO₆ phosphor. The charge transfer band was observed in the excitation spectra of Sm³⁺ or Dy³⁺ doped LaBWO₆ phosphors. Present investigation indicated that Sm³⁺ and Dy³⁺ doped LaBWO₆ can be applied in solid state lighting and LaBWO₆ is a promising host for display applications.     

Enhancement of red fluorescence and afterglow in CaWO4:Eu3+ by addition of MoO3

In this study, Eu³⁺ doped Ca(WO₄)_1?x(MoO₄)_x phosphors were synthesized via high temperature solid-state reaction. Compared with the Eu³⁺ activated CaWO₄ sample, an increment of MoO₃ doping concentration could improve the emission intensity. Improved red afterglow originating from the ⁵D₀ to ⁷F_J (J = 0, 1, 2, 3, 4) transitions of Eu³⁺ was observed after appropriate amount of MoO₃ was added, and the optimal MoO₃ doping concentration was experimentally determined to be 0.02. The proposed explanation for the afterglow property was also discussed.     

Design and characterization of new lanthanide fluorides and their optical properties

Three kinds of lanthanide phosphors (La_xLu_1−xF₃: Eu³⁺, LaF₃–CaF₂:Eu³⁺ and LaF₃: Eu³⁺) have been successfully synthesized based on three different ways such as molten salts, co-precipitation, supersonic and microwave irradiations. The as-prepared powder materials all exhibited red luminescence. Their crystal structures or morphologies were studied by means of X-ray powder diffraction and scanning electronic microscope. Eu³⁺-doped LaF₃–CaF₂ phosphor can be emissive under excitation at longer wavelengths (466 and 533 nm) excitations. Supersonic and microwave irradiations have shortened the reaction time of LaF₃: Eu³⁺ crystals in 40 min under very low temperature (50 °C).     

Facile synthesis of lanthanide vanadates and their luminescent properties

GdVO₄:Eu³⁺, Bi³⁺ with tetragonal phase has been successfully synthesized by employing efficient irradiations. The assembly of composites with fine grains based on acoustic energy and microwave radiation requires low temperature (90 °C) and short reaction time (60 min). All the compounds exhibited red emissions and they can be sensitized through the doped Bi³⁺ ions. The dependence of pH changes and doping concentration on the fluorescence features has been discussed. The photoluminescence measurements show that the optical properties achieved the best results at pH = 9 for GdVO₄:Eu³⁺(5 mol%), Bi³⁺(1 mol%) or pH = 7 for GdVO₄:Eu³⁺.     

White and tunable light emission of Ho3+ and Pr3+ ions co-doped phosphate glasses

The Ho³⁺ and Pr³⁺ ions co-doped phosphate glasses were prepared by melt quenching procedure with the various composition of (70-x-y)P₂O₅ + 20SiO₂ + 10CaO + xHo₂O₃ + yPr₂O₃ (x = 0.4, 0.6, 0.8, 1.0 mol%, y = 0.6, 0.8, 1.0 mol%). The structural investigation (based on X-ray diffraction analysis) confirmed amorphous character of these glass materials. The optical properties were studied. The glass samples have strong absorption at 360 nm, and the excitation light at 360 nm can excite Ho³⁺ and Pr³⁺ ions very well, causing them to produce synergistic luminescence. The glass sample 68.8P₂O₅ + 20SiO₂ + 10CaO + 0.4Ho₂O₃ + 0.8Pr₂O₃ emits strong white light under 360 nm excitation. The chromaticity coordinate values are x = 0.3378, y = 0.3472 in white light region, and it has a moderate correlated color temperature (CCT) of 5277 K. Decay time data reveals that there is energy transfer from Pr³⁺ to Ho³⁺ ions. This glass will be a good material for white light and tunable light emitting.     

Cationic P⋯N interaction in XH3P+⋯NCY complexes (X = H,F, CN,NH2, OH; Y = H,Li, F,Cl) and its cooperativity with hydrogen/lithium/halogen bond

The geometries, interaction energies and bonding properties of cationic pnicogen bond (CPB) interactions are studied in binary XH₃P⁺⋯NCY (X = H, F, CN, NH₂, OH; Y = H, Li, F, Cl) complexes by means of MP2/aug-cc-pVTZ calculations. Interaction energies of these binary complexes span a large range, from −16.36 kcal/mol in (NH₂)H₃P⁺⋯NCF to −71.36 kcal/mol in FH₃P⁺⋯NCLi complex. The spin–spin coupling constant across P⋯N interaction depends considerably on the nature of X and Y substituents. The characteristic of CPB interactions is analyzed in terms of parameters derived from quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. The charge transfer from the nitrogen base to the cationic acid stabilizes these pnicogen–bonded complexes. For a given XH₃P⁺, the net charge transfer value increases as the interaction energy of the complex becomes more negative, i.e., NCLi > NCCl > NCH > NCF. Moreover, mutual influence between the CPB and hydrogen/halogen/lithium bond is studied in the ternary XH₃P⁺⋯NCY⋯NCH complexes. The results indicate that the formation of a Y⋯N interaction tends to strengthen CPB in the ternary systems.     

Phase equilibria in Fe–Sn–Ti ternary system at 1073 K and 1273 K

Phase equilibria in the Fe–Sn–Ti ternary system at 1073 and 1273 K were experimentally investigated through alloy sampling approach facilitated with electron probe micro-analyzer and X-ray diffraction. Two ternary compounds TiFe₂Sn and Ti₂FeSn were detected. Ten 3-phase equilibria at 1073 K, including β(Ti)+Ti₃Sn+FeTi, Ti₃Sn+FeTi+Ti₅Sn₃, FeTi+Ti₅Sn₃+Ti₂FeSn, Ti₂FeSn+Fe₂Ti+TiFe₂Sn, Ti₂FeSn+Ti₅Sn₃+Ti₆Sn₅, FeTi+Fe₂Ti+Ti₂FeSn, Ti₂FeSn+Ti₆Sn₅+TiFe₂Sn, TiFe₂Sn+Ti₆Sn₅+Liquid, TiFe₂Sn+Fe₅Sn₃+Liquid and α(Fe)+Fe₂Ti+TiFe₂Sn, and seven 3-phase equilibria including β(Ti)+Ti₃Sn+FeTi, Ti₃Sn+FeTi+Ti₅Sn₃, Ti₃Sn+Ti₂Sn+Ti₅Sn₃, FeTi+Fe₂Ti+Ti₅Sn₃, Fe₂Ti+Ti₂FeSn+Ti₅Sn₃, Ti₂FeSn+Fe₂Ti+TiFe₂Sn and Ti₂FeSn+Ti₆Sn₅+TiFe₂Sn at 1273 K were experimentally confirmed. At 1073 K, the homogeneity ranges of Ti₂FeSn were 45.5–51.4 at% Ti and 24–27.7 at.% Sn while TiFe₂Sn exhibited a large homogeneity range of 46.9–66.4 at% Fe and 22.7–26.4 at% Sn, the solubility of Sn in Fe₂Ti,Fe in Ti₅Sn₃, Ti in Fe₅Sn₃ and Fe in Ti₆Sn₅ can be up to 4.6 at.%, 10.2 at%, 3.7 at% and 21 at%, respectively, while at 1273 K, Solubility of Sn in Fe₂Ti considerably increased to 10.8 at%, Fe in Ti₅Sn₃ changes little. According to the measured phase relations, an invariant reaction was further deduced, which was Fe₂Ti+Ti₅Sn₃↔FeTi+Ti₂FeSn occurring between 1073 K and 1123 K.     

The enhancing effect of a cation-π interaction on the cooperativity of halogen bonds: A computational study

In this work, we investigate the effect of a cation-π interaction on the cooperativity of X⋯N halogen bonds in PhX⋯NCX⋯NH₃ complexes, where Ph = phenyl and X = Cl, Br, I. Molecular geometries and interaction energies of the resulting complexes are studied at the MP2/aug-cc-pVDZ(-PP) computational level. The mechanism of the cooperativity between halogen bonds is analyzed using parameters derived from the noncovalent index, quantum theory of atoms in molecules and natural bond orbital methodologies. It is found that the divalent cations (Be²⁺, Mg²⁺) have a larger influence on the cooperativity of halogen bonds than monovalent ones (Li⁺, Na⁺). The formation of a cation-π interaction leads to strengthening of the halogen bonds, hence increases their cooperativity.     

Investigation of spectroscopic properties of Sm-Eu codoped phosphate glasses

Phosphate glasses with chemical compositions of 74.5NaH₂PO₄–20ZnO–5Li₂O–0.5Sm₂O₃ and 74NaH₂PO₄–20ZnO–5Li₂O–0.5Sm₂O₃–0.5Eu₂O₃ were synthetized by melt quenching method. We investigated the influence of Sm³⁺/Eu³⁺ doping on the optical properties of phosphate glasses. X-ray Diffraction indicates that the samples have an amorphous structure. DSC measurements show a good thermal stability of phosphate glasses. Using the absorption spectra, Judd–Ofelt analysis was applied to absorption bands of Sm³⁺ (4f⁵) to carry out the three phenomenological parameters of Judd–Ofelt (JO). According to the obtained values of Ω₂, Ω₄ and Ω₆, some radiative properties were theoretically determined. We report both the photoluminescence (PL) and the PL lifetime measurements of a prominent emission transition ⁴G_5/2 → ⁶H_5/2 (604 nm) of Sm³⁺ both in absence and in presence of Eu³⁺. It is shown that Eu³⁺ ions act as sensitizers for Sm³⁺ ions and contribute largely to the improvement of the radiative properties of phosphate glasses. An improvement of the PL lifetime value after adding Eu³⁺ ions (4.58 ms) is reported. The predicted lifetime (τ_rad) calculated by Judd–Ofelt theory and the experimental lifetime (τ_meas) for the prepared phosphate glasses were compared with those of other works. Photoluminescence (PL) intensity of ⁴G_5/2 → ⁶H_5/2 (604 nm), ⁴G_5/2 → ⁶H_7/2 (567 nm), ⁴G_5/2 → ⁶H_9/2 (650 nm) and ⁴G_5/2 → ⁶H_11/2 (706 nm) and the quantum efficiency (η) for the excited ⁴G_5/2 level were enhanced after adding Eu³⁺. The radiative properties obtained for (Sm, Eu) codoped phosphate glasses suggest that the present material can be a potential candidate for the development of color display devices.     

Red phosphor Li2Mg2(WO4)3: Eu3+ with lyonsite structure for near ultraviolet light-emitting diodes

A series of Eu³⁺-activated Li₂Mg₂(WO₄)₃ (LMW) materials were synthesized by high temperature solid state reactions. The phosphor can be effectively excited by 394 nm near ultraviolet light and emit intense red light with high color purity. Prepared phosphors can be indexed to LMW with particular lyonsite structure. The occupation of Eu³⁺ in LMW is selective. Most of Eu³⁺ comes into ¹A sites without inversion symmetry. The present research suggests that LMW is a suitable host for luminescence applications and Eu³⁺-activated LMW is a promising phosphor for phosphor-converted white light-emitting diodes.     

A molecular dynamic study on the dissociation mechanism of SI methane hydrate in inorganic salt aqueous solutions

Gas hydrate is not only a potential energy resource, but also almost the biggest challenge in oil/gas flow assurance. Inorganic salts such as NaCl, KCl and CaCl₂ are widely used as the thermodynamic inhibitor to reduce the risk caused by hydrate formation. However, the inhibition mechanism is still unclear. Therefore, molecular dynamic (MD) simulation was performed to study the dissociation of structure I (SI) methane hydrate in existence of inorganic salt aqueous solution on a micro-scale. The simulation results showed that, the dissociation became stagnant due to the presence of liquid film formed by the decomposed water molecules, and more inorganic ions could shorten the stagnation-time. The diffusion coefficients of ions and water molecules were the largest in KCl system. The structures of ion/H₂O and H₂O/H₂O were the most compact in hydrate/NaCl system. The ionic ability to decompose hydrate cells followed the sequence of: Ca²⁺ > 2K⁺ > 2Cl⁻ > 2Na⁺.     

Evolution of structure,stability, and nonlinear optical properties of the heterodinuclear CNLin (n = 1–10) clusters

The lowest-energy structures and stabilities of the heterodinuclear clusters, CNLi_n (n = 1–10) and relevant CNLi_n⁺ (n = 1–10) cations, are studied using the density functional theory with the 6-311 + G(3df) basis set. The CNLi₆ and CNLi₅⁺ clusters are the first three-dimensional ones in the CNLi_n^0/+ series, respectively, and the CN group always caps the Li_n^0/+ moiety in the CNLi_n^0/+ (n = 1–9) configurations. The CN triple bond is found to be completely cleaved in the CNLi₁₀^0/+ clusters where the C and N atoms are bridged by two Li atoms. The CNLi_n (n = 2–10) clusters are hyperlithiated molecules with delocalized valence electrons and consequently possess low VIP values of 3.780–5.674 eV. Especially, the CNLi₈ and CNLi₁₀ molecules exhibit lower VIPs than that of Cs atom and can be regarded as heterobinuclear superalkali species. Furthermore, these two superalkali clusters show extraordinarily large first hyperpolarizabilities of 19,423 and 42,658 au, respectively. For the CNLi_n⁺ cationic species, the evolution of the energetic and electronic properties with the cluster size shows a special stability for CNLi₂⁺.     

A new red colour emitting phosphor – ZnS:Mn co-doped with Ba for electroluminescent (EL) displays

A new Mn activated Ba co-doped ZnS phosphor shows an interesting shift in the spectral emission from amber-yellow (570 nm) to red (620 nm) colour. To realize the phosphor material physics, attempts were made to fine tune the band gap of ZnS by co-doping Ba within the concentration range 2.50–10 mol%. Ba co-doping in ZnS host was achieved by sintering BaSO₄ with ZnS at 900 °C by carbothermal reduction method. Measurement of the CIE (Commission International deEchairge) chromaticity colour coordinates (x, y) of Zn_0.99S:Mn_0.01 and Ba_0.10Zn_0.89S:Mn_0.01 phosphors shown to be (0.53, 0.47) and (0.65, 0.32), respectively.     

Dysprosium doped di-strontium magnesium di-silicate white light emitting phosphor by solid state reaction method

Dysprosium doped di-strontium magnesium di-silicate namely Sr₂MgSi₂O₇:Dy³⁺ phosphor was prepared by the solid state reaction method. The phase structure, surface morphology, particle size, elemental analysis was analyzed by using XRD, TEM, EDX and FTIR techniques. The EDX and FTIR spectra confirm the present elements in Sr₂MgSi₂O₇:Dy³⁺ phosphor. The optical properties of Sr₂MgSi₂O₇:Dy³⁺ phosphor was investigated utilizing thermoluminescence (TL), photoluminescence (PL), long lasting phosphorescence and mechanoluminescence (ML). Under the ultraviolet excitation, the emission spectra of Sr₂MgSi₂O₇:Dy³⁺ phosphor are composed of a broad band and the characteristic emission of Dy³⁺ peaking at 470 nm (blue), 575 nm (yellow) and 678 nm (red), originating from the transitions of ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → ⁶H_11/2. CIE color coordinates of Sr₂MgSi₂O₇:Dy³⁺ are suitable as white light emitting phosphor. Decay graph indicate that this phosphor also contains fast decay and slow decay process. The peak of ML intensity increases linearly with increasing impact velocity of the moving piston. The possible mechanism of this white light emitting long lasting phosphor is also investigated.