Search

Lanthanide luminescence is characterised by "forbidden" 4f–4f transitions and a complicated electronic structure. Our understanding of trivalent lanthanide(III) ion luminescence is centered on Eu3+ because absorbing and emitting transitions in Eu3+ occur from a single electronic energy level. In Sm3+ both absorbing and emitting multiplets have a larger multiplicity. A band arising in transitions from the first emitting state multiplet to the ground state multiplet will have nine lines for a Sm3+ complex. In this study, high-resolution emission and excitation spectra were used to determine the electronic energy levels for the lowest multiplet and first emitting multiplet in four Sm3+ compounds with either tricapped trigonal prismatic TTP or capped square antiprismatic cSAP coordination polyhedra but different site symmetry. This was achieved by the use of Boltzmann distribution population analysis and experimentally determined transition probabilities from emission and excitation spectra. Using this analysis it was possible to show the effect of changing three oxygen atoms with three nitrogen atoms in the donor set for two compounds with the same coordination polyhedra and site symmetry. This work celebrates the 40th anniversary of Kirby and Richardson's first report of [Eu(ODA)3]3− luminescence. [ABSTRACT FROM AUTHOR]

Nine lanthanide-organic frameworks [Ln(L)1.5(H2O)3] (1-Ce, 2-Dy, 3-Eu, 4-Gd, 5-Ho, 6-Nd, 7-Pr, 8-Sm, and 9-Tb; H2L = 4,4'-(1,2-dihydroxyethane-1,2-diyl)dibenzoic acid) have been synthesized under solvothermal conditions. Single-crystal X-ray diffraction analyses show that compounds 1-9 are isomorphic, in which each Ln atom is linked by L ligands to form a 3D framework with an unprecedented 4,4,6-connected topology. All these compounds have excellent solvent stability and can remain stable in boiling water for up to a week. Moreover, these compounds exhibit metal-dependent luminescence and magnetic properties. 3-Eu and 9-Tb exhibit relatively good fluorescence properties, 4-Gd shows ferromagnetic coupling, and the other compounds present antiferromagnetic coupling. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) emissive probes are becoming increasingly popular in biological sensing and imaging due to the advantages of non-invasiveness and deep tissue-penetrating ability. Herein, a series of complexes of trivalent lanthanide ions (Ln = Yb, Er, and Gd) with the commercially available azo dye chromophore 2R (Na2H2C2R) as ligand and featuring respectively H2O and dimethylsulfoxide (DMSO) as ancillary ligands have been prepared. Formulated as [Ln2(HC2R)2(H2O)10]·8H2O (1-3, Ln = Yb, Er, Gd) and [Ln2(HC2R)2(DMSO)10]·2DMSO (4-6, Ln = Yb, Er, Gd), their structures have been determined by singlecrystal X-ray diffraction studies. Photophysical property studies revealed NIR emissions of the DMSO complexes characteristic of Yb(III) and Er(III), effectively sensitized by the dye ligand arising mainly from the π-π* transition of the chromophore. The long-wavelength excitation of the complexes, covering the whole visible-light range and extending into the NIR region, portends the potential applications of such complexes for flexible bioimaging and sensing. [ABSTRACT FROM AUTHOR]

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are considered as next-generation of NIR light sources for spectroscopy. However, it is still a challenge to develop an inexpensive broadband NIR phosphor with relatively long-wavelength (λem > 800 nm) emission. In this work, an octahedral Al3+-containing pyrophosphate Al0.5Ta0.5P2O7 with a cubic structure was chosen as a host for Cr3+. Synthesizing this material indicates that this phosphor exhibits a broadband NIR emission peaking at 850 nm with a full width at half maximum (FWHM) of 155 nm under 465 nm excitation. The crystal structure, morphology, local structure, and photoluminescence properties of this material were investigated in detail. The results revealed a full understanding of this new material. A NIR pc-LED device fabricated by using this material combined with a 450 nm LED chip generates a NIR output power of 10.7 mW and a NIR photoelectric conversion efficiency of 3.4% under a 100 mA driving current, which shows the possibility of this material to be utilized in NIR pc-LED applications. Moreover, this material exhibits a linear relationship between emission intensity, decay time and temperature in a wide temperature range, implying that excellent multi-model temperature sensing applications can be expected. [ABSTRACT FROM AUTHOR]

Multi-band emission characteristics open up more possibilities for the application of phosphors in LEDs. In this work, a novel Bi3+-activated Sr3NaSbO6 phosphor is developed. The Bi3+ occupation, luminescence properties and application in LEDs of the phosphor are investigated and discussed. There are Sr and Na sites in the crystal structure for Bi3+ substitution, corresponding to two different luminescence centers, which can be excited by commercial UV chips. By changing the excitation wavelength, Bi3+ in the two lattice sites can be excited separately, and a switchable multi-band emission can be obtained accordingly. The blue emission peaks at 450 nm, and the other emission has an ultra-wide full-width at half-maximum of 206 nm, which can cover a wider visible spectrum. All the results show that the phosphor has application prospects in LEDs. [ABSTRACT FROM AUTHOR]

The discovery of phosphors with highly efficient broadband near-infrared emission is urgent for constructing NIR sources for various applications. Herein, we synthesized a series of near-infrared emitting garnet-type (A3B2C3O12) Lu2−xCaAl3.99Cr0.01SiO12:xGd/La and Lu2CaAl3.99−yCr0.01SiO12:ySc/Ga phosphors and systematically investigated the effect of A/B-site substitution on the crystal structure and luminescence properties. Structural and optical analyses revealed that the A/B-site substitution weakened the crystal field strength, further enhancing the broadband emission of the allowed 4T2 → 4A2transition and diminishing the narrow-peak emission of the forbidden 2E → 4A2 transition. As expected, NIR phosphors, exemplified by Lu1.7CaAl3.99Cr0.01SiO12:0.3Gd and Lu2CaAl3.49Cr0.01SiO12:0.5Sc, showed outstanding thermal stabilities at 423 K (150 °C) registering values of 103.02% and 94.91%, with high quantum efficiencies of 80.48% and 85.01%, respectively. In addition, pc-LEDs with broadband NIR output and good optoelectronic properties have been realized, demonstrating the great potential of broadband NIR pc-LEDs for applications. This work not only provides a series of high-efficiency phosphors for NIR pc-LED applications, but also provides a systematic idea and an efficient method to improve the luminescence performance of garnet-type phosphors. [ABSTRACT FROM AUTHOR]

Despite extensive research on the photoluminescence properties of Bi3+ ions, the origins of their emission and excitation bands remain elusive. Herein, we present a comprehensive analysis of the photoluminescence properties of Bi3+-activated LuXnGaO4 (Xn = Mg, Zn), elucidating the underlying factors governing the intra-ionic and extra-ionic electronic transitions. By integrating crystal structure data and spectroscopic data analyses with semi-empirical formula calculations, the origins of excitation and emission states were elucidated. Moreover, the impact of alterations in chemical surroundings on the luminescence of Bi3+ was investigated. Both LuXnGaO4:Bi3+ phosphors exhibit three excitation peaks in the near ultraviolet region and display a broadband yellow emission. However, the luminous behavior of LuMgGaO4:Bi3+ and LuZnGaO4:Bi3+ differs due to variations in the band gap, bond length and neighboring atoms. It is anticipated that the investigation of Bi3+-activated gallates presents a promising avenue for advancing wide-band and long-wavelength emitting phosphors. [ABSTRACT FROM AUTHOR]

The development of novel phosphors with excellent luminescence properties for white light-emitting diodes (WLEDs) is always a formidable task. Compared with the traditional laborious and aimless "trial and error" experiments, a mineral-inspired prototype strategy can provide an efficient and accurate method. Herein, for the first time, a novel yellow-emitting phosphor NaBaY2(PO4)3:Eu2+ was discovered using the mineral-inspired prototype strategy and cation substitution method. The phosphor was prepared via the high-temperature solid-state reaction method, and its crystal structure, luminescence properties and potential application for WLEDs were systematically investigated. The NaBaY2(PO4)3 phase was derived from the K2Mg2(SO4)3-type mineral structure and a photoluminescence study revealed that the phosphor can emit bright yellow light with a maximum at 545 nm upon excitation at 351 nm. A WLED lamp was fabricated by the use of a blend of commercial blue-emitting BaMgAl10O17:Eu2+, yellow-emitting NaBaY2(PO4)3:Eu2+ and red-emitting (Ca, Sr)AlSiN3:Eu2+ phosphors with a 380 nm LED chip. The CIE, CCT, Ra and efficiency of the as-fabricated LEDs were measured to be equal to (0.366, 0.365), 4327 K, 91.2 and 40.8 lm W−1, respectively. These results suggest that NaBaY2(PO4)3:Eu2+ could be a promising candidate for n-UV WLEDs. [ABSTRACT FROM AUTHOR]

The reaction among [Au2Ag2(C6F5)4(OEt2)2]n, PbCl2 and terpyridine leads to the polymeric complex [{Au(C6F5)2}2{Pb(terpy)}]n (1). Its crystal structure reveals potential voids close to the lead centres large enough to hold different molecules. The availability of these free sites allows complex 1 to act as a VOC sensor. Thus, when 1 is exposed to different solvent vapours such as acetonitrile, toluene or THF, variations in its solid appearance and its photophysical properties are observed as a consequence of the formation of the new polymorphs [{Au(C6F5)2}2{Pb(terpy)(CH3CN)2}]n (2), [{Au(C6F5)2}2{Pb(terpy)}]n·Tol (3) and [{Au(C6F5)2}2{Pb(terpy)(THF)}]n·THF (4). Each polymorph displays a different emission energy depending on its structure and the presence of metallophilic interactions. In addition, the reversible solvent molecule exchange allows the tuning of the luminescence emissions in the greenish yellow–red range. DFT and TD-DFT calculations were performed to explain the origin of the luminescence of all these complexes. [ABSTRACT FROM AUTHOR]

In recent years, the research and development of new white LEDs have attracted extensive attention. Whether the new LEDs have a higher color rendering index and can simulate natural sunlight without damaging human health is the issue of concern. Therefore, we introduce in detail the ultraviolet (UV) excited luminescence characteristics of Eu ions, Ce ions, and other ions in different host lattice (aluminate, silicate, phosphate, and borate) matrices. This paper summarizes the introduction and application of rare-earth ions as activation center phosphors and expounds on the application potential of cyan and blue phosphors in many fields such as display technology from the aspects of excitation and emission characteristics, lifetime, color purity, and thermal stability. Finally, we put forward our views on improving the thermal stability of phosphors and selecting crystals with suitable structures as the host for the preparation of phosphors. [ABSTRACT FROM AUTHOR]

Luminescent materials used in solid-state lighting usually face the challenge of the adjustment of luminescence properties. The coordinated luminescence of two activators in luminescent materials is a good method. Herein, CaAl2Si2O8:Dy3+, CaAl2Si2O8:Eu3+, and CaAl2Si2O8:Dy3+, Eu3+ with a pure phase (CaAl2Si2O8) were synthesized in air. The X-ray diffraction patterns of the samples were measured and their crystal structures were elucidated. Under excitation at 350 nm, the yellow emission of CaAl2Si2O8:Dy3+ in the spectral range of 525–800 nm was observed due to the 4F9/2 → 6H15/2, 6H13/2, 6H11/2, and 6H9/2 transitions of Dy3+ ions. CaAl2Si2O8:Eu3+ showed red emission in the range of 550–720 nm because of the transitions 5D0 → 7F1, 7F2, 7F3, and 7F4 of Eu3+ ions when it was excited by 394 nm light. A tunable color emission of CaAl2Si2O8:Dy3+, Eu3+ from yellow to red was found when the ratio between Dy3+ and Eu3+ ions was changed. We investigated the concentration-dependent spectra and ensured the optimal Dy3+ and Eu3+ concentrations in host CaAl2Si2O8. The spectra of the samples manifested the energy transfer from Dy3+ to Eu3+ ions. The energy-level diagrams of Dy3+ and Eu3+ ions were used to analyze the luminous mechanism of the samples. The research results are beneficial to the development of other Dy3+ and Eu3+ co-doped luminescence materials. [ABSTRACT FROM AUTHOR]

Recently, great advances have been made in the mechanochromic luminescence (MCL) of organic crystals that can switch their emission colors upon exposure to mechanical stimuli. Although several polymorphic crystals and solvates have exhibited multicolor MCL properties, a further deep understanding of the relationship between crystal structures and stimuli-responsive properties is required for rationally generating multicolor-emissive polymorphic crystals and solvates from a single luminescent compound. Herein, multicolor luminescence switching has been achieved for solvates of a phenanthroimidazolylbenzothiadiazole derivative with dianisyl groups. Four types of solvates with different luminescence properties changed their emission colors upon amorphization induced by mechanical stimuli. The amorphous state was recrystallized into solvates when exposed to solvent vapors. Furthermore, the solvate containing pyridine molecules showed a bathochromic shift in emission wavelength upon exposure to acid vapor. Typical acid-responsive luminescence switching is characterized by the protonation of the basic moiety of luminescent molecules, whereas in this study, the change in luminescence color could be induced by protonating non-luminescent pyridine molecules in the solvate. The present study potentially provides useful insights for the development of smart luminescent sensors. [ABSTRACT FROM AUTHOR]

The majority of the fabrication procedures of lanthanide-doped materials involve thermal treatment that often results in crystallite regrowth, stabilizing the specific crystal structure and resulting in luminescence enhancement. The efficiency and intensity of up-conversion luminescence are closely related to the structure and synthesis process of the materials. Herein, well-crystallized and pure tetragonal NaY(MoO4)2 microcrystals with a uniform octahedral shape have been successfully synthesized via an environmentally friendly hydrothermal method, followed by annealing treatment. The phases, structures, morphologies, and compositions of the synthesized products annealed at 500–1000 °C remain unchanged, indicating high thermal stability. Furthermore, the NaY(MoO4)2:Yb3+/Er3+ microcrystals exhibit strong green emission when irradiated using infrared (980 nm) or ultraviolet (378 nm) wavelengths. Upon 980 nm excitation, up to 37-fold luminescence enhancement is achieved when the samples are annealed at about 700 °C. Interestingly, the high colour purity of the strong green emission is not only independent of the dopant concentration and heat treatment temperature, but it is also independent of the excitation conditions, including power and wavelength, and this makes it particularly suitable as a green safety signal light and luminescent security ink in paintings. As-prepared safety inks with NaY(MoO4)2:Yb3+/Er3+ microcrystals were used for visual fingerprint recognition printed on A4 paper with three-level fingerprint security features, significantly increasing the difficulty of illegal imitation and enhancing the levels of anti-counterfeiting. [ABSTRACT FROM AUTHOR]

The compound Li3SiNO2:Eu2+ was synthesized in high temperature solid-state reactions in weld shut tantalum ampules and the crystal structure of Li3SiNO2 has been determined by single-crystal X-ray diffraction. It crystallizes in the monoclinic space group C2/c (no. 15) with the lattice parameters a = 1049.01(3), b = 1103.42(3), c = 511.86(2) pm, β = 116.14(1)°, and a volume of V = 0.53187(2) nm3. This compound is built up from two different layers, which are arranged alternately along the crystallographic a-axis. The results from single-crystal diffraction were confirmed by the Rietveld analysis of bulk samples. Moreover, Li3SiNO2 could be successfully doped with the activator ion Eu2+ and the luminescence spectroscopy of single-crystals revealed broad band emission at λmax = 601 nm (fwhm = 90 nm). [ABSTRACT FROM AUTHOR]

In this work, a series of Cr3+-doped A2NaYF6 (denoted as ANYF:Cr; A = K, Rb, and Cs) fluoroyttrate double-perovskites with broad blue excitation and near-infrared (NIR) emission bands were prepared using a high-temperature solid-state reaction method. The physicochemical and spectroscopic properties of the as-prepared products, including crystal structure, bandgap, morphology, luminescence behaviour and optical performance, were studied in detail. The results show that the Cr3+ activators undergo a decreasing crystal field in ANYF in the direction from K to Cs, yielding a red shift of the emission peak position from 758 to 786 nm, whilst the full-width-at-half-maximum (FWHM) expands from 98 to 104 nm. By virtue of the broadband NIR emission, clear structural images of the tangerine section, mini LED flashlight and circuit board were obtained by merging the optimal RNYF:Cr phosphor on a blue InGaN chip, implying its potential use in light-emitting diodes for non-destructive testing. [ABSTRACT FROM AUTHOR]

Two new alkali-earth and rare-earth metal borates, Sr2Tb3B27−δO46 and Ba2Eu3B27−δO46 (δ = 2/3), have been prepared by high-temperature solution reactions at 950 °C. The single-crystal XRD analysis showed that the borates crystallize in the rhombohedral space group R3 with the cell parameters a = 7.7468(1) Å, c = 46.3657(5) Å, V = 2409.75(3) Å3, Z = 3 and a = 7.7964(1) Å, c = 46.5086(6) Å, V = 2448.23(7) Å3, Z = 3, respectively, which further confirms that "LnMB9O16" has the right formula of M2Ln3B27−δO46 (δ = 2/3). Their crystal structures consist of 3D networks constructed by Tb(Eu)O6 trigonal prisms, BO3 planar triangles, and BO4 tetrahedra, with large cavities accommodating Sr2+ (Ba2+) cations. Furthermore, the phase composition, morphology, IR, Raman, and XPS spectra as well as photoluminescence properties of these two compounds were studied. Upon excitation by ultraviolet radiation, Sr2Tb3B27−δO46 exhibits the characteristic emission lines originating from Tb3+ corresponding to 5D4–7F6,5,4,3,2,1,0 transitions, whereas Ba2Eu3B27−δO46 displays bright red emission from Eu3+ with four groups of emission bands associated with 5D0 → 7F1,2,3,4 transitions. Both phosphors show stable luminescence and color purity at elevated temperatures. As it may be expected, Sr2Tb3B27−δO46 and Ba2Eu3B27−δO46 (δ = 2/3) are promising green (Tb) and red (Eu) components for use in WLEDs. [ABSTRACT FROM AUTHOR]

Exploring new visible laser crystals is of great significance to the development of diode pumped all-solid-state visible lasers and solid-state lighting. In this work, a high concentration (10 at%) Er3+ ion singly doped GdTaO4 single crystal with high quality as a promising visible laser crystal was grown successfully by the Czochralski method. The structure of the crystal was determined to be a monoclinic structure with the space group C2/c by powder and single-crystal X-ray diffraction characterization techniques. The absorption and blue and violet light excited emission spectra of the crystal were obtained and analyzed. A strong emission band centered at 555 nm was observed under excitation at both 450 nm and 377 nm. The absorption cross-section at 450 nm and emission cross-section at 555 nm were calculated to be 4.60 × 10−21 and 4.57 × 10−21 cm2, respectively, which are comparable to those of other promising InGaN diode pumped visible laser crystals doped with rare earth ions (Er3+, Dy3+ and Pr3+). Under 450 nm or 355 nm laser excitation, the crystal emits strong green fluorescence. A 380 nm LED chip pumped prototype device was fabricated using the crystal, which exhibited green light under the driving current. Besides, the green and red upconversion luminescence of Er3+ in the GdTaO4 single crystal was found to be a two-photon process under the excitation of a 980 nm laser. All these results strongly recommend that the 10 at% Er3+ ion doped GdTaO4 crystal is very promising for diode pumped green lasers and probably useful for solid-state lighting. [ABSTRACT FROM AUTHOR]

A series of solid-solution phosphate germanates Ca8+0.5xZnEu(PO4)7−x(GeO4)x (x = 0, 0.2, 0, 4, 0.6, 0.8, 1) with the β-Ca3(PO4)2-type structure were synthesized by solid-state reactions. The limit of existence of a single-phase solid solution was determined by X-ray diffraction patterns and it was found at x = 0.8. The heterovalent tetrahedral [PO4]3− → [GeO4]4− substitution requires a charge compensation according to the scheme: [PO4]3− + ½ □ → [GeO4]4− + ½ Ca2+. The additional amount of Ca2+ ions in the crystal structure was detected at the M4 site during Rietveld refinement. It was shown that in β-Ca3(PO4)2-type compounds, charge balancing is not provided by the randomly distributed oxygen vacancies but only by the partial occupancy of the M4 site. The presence of Ca2+ at the M4 site leads to a polar structure with the space group R3c which was confirmed by an SHG test for all single-phase samples. It was shown that the Ge4+ ions preferably occupy the T3 site in the structure, which is connected through common oxygen with the cationic M1–M5 sites. The analysis of the similarity of the previously reported Ca9La(GeO4)0.75(PO4)6 compound reveals an unexpectedly high value. The same structural similarity evaluation of the studied compound Ca8.1EuZn(PO4)6.8(GeO4)0.2 in the present work with the initial model gives a very small value, which indicates a good match between the initial and under-consideration structures. The luminescence properties of Eu3+ were investigated from the point of view of crystal structures and anionic substitutions. The integral intensity increased linearly with the [PO4]3− → [GeO4]4− substitution. It can be concluded that the anionic substitution on Ge4+ can improve the luminescence characteristics. The present study includes new data on the anionic substitution based on accurate crystal structure refinement. [ABSTRACT FROM AUTHOR]

Mn4+-activated oxide red phosphors are always a hot topic in the luminescent material field to solve the lack of red light components in white-light-emitting diodes (WLEDs). Herein, a series of novel deep red-emitting CaAl12−mPmO19+m:0.01Mn4+,0.2Mg2+ (m = 0–0.15) phosphors were synthesized and their crystal structure, luminescence properties and thermal stability were investigated in detail. The high-valence P5+ is used to replace low-valence Al3+ in the luminescent host CaAl12O19 to improve the photoluminescence quantum yield (PLQY) of phosphors. The doping of P5+ does not change the crystal phase structure of phosphors, and the luminescence intensity and PLQY are significantly enhanced. The analysis of the photocurrent and fluorescence lifetime shows that an electron trap with a quantum-confinement structure is formed in the phosphor host, which plays a key role in buffering photogenerated electrons. Therefore, the PLQY of the P5+-doped CaAl11.90P0.1O19.10:0.01Mn4+,0.2Mg2+ phosphor increased from 9.8% (P5+-undoped) to 70.2%, and the mechanism of PLQY enhancement is proposed based on the analysis of the crystal structure. Furthermore, the phosphor has superior thermal stability and color purity (96.8%). Overall, this work provides new insights and ideas on quantum confinement effects for improving the quantum yield of Mn4+-activated luminescent materials. [ABSTRACT FROM AUTHOR]

The past decade has witnessed rapid advances in the development of organic crystals that exhibit mechanochromic luminescence (MCL), i.e., the reversible color change of photoluminescence induced by mechanical force. However, a greater understanding of the correlation between the MCL properties and the molecular structures in the crystalline state is still necessary to rationally control the photophysical and mechanical properties of organic crystals. Herein, a thienyl-substituted benzothiadiazole derivative is described as a new donor–acceptor-type MCL dye that crystallizes in three polymorphic forms. Both bicolor and tricolor MCL have been realized by the single donor–acceptor-type dye. The green-emissive polymorph exhibits typical bicolor MCL between green and orange based on crystal-to-amorphous phase transitions. Meanwhile, the yellow and yellow-orange-emissive crystals show tricolor emission-color switching. Specifically, the emission color of the yellow-emissive crystals changed to yellowish orange and orange in response to thermal and mechanical stimuli, respectively. The yellow-orange-emissive crystals display bicolor MCL between yellow-orange and orange emission. The single-crystal X-ray diffraction analyses of the polymorphic crystals indicated that the emission color of these crystals should be determined by the dihedral angle between benzothiadiazole and thiophene rings as well as the mode of packing structures. This study reinforces the understanding of the MCL of polymorphic crystals, which should help to advance the possible applications of MCL crystals in multi-color mechanosensing systems. [ABSTRACT FROM AUTHOR]

In this work, we present a brand-new narrowband red-emitting fluoroperovskite via the introduction of Mn4+ into NaZnF3 through a facile co-precipitation method at room temperature. The physicochemical properties of the fluoroperovskite such as crystal and electronic structures, morphology, and elemental composition, as well as its spectroscopic properties such as luminescence behaviours and optical performance were characterized and investigated in detail. Evidence shows that NaZnF3:Mn4+ exhibits a uniform particulate shape with single-phase crystallinity. By virtue of the non-equivalent substitution and the [MnF6] octahedral distortion in the fluoride host, sharp red emissions of phonon sidebands and the zero-phonon line upon blue light excitation are identified. Benefiting from the unique spectral feature, a wide colour gamut of 104.1% NTSC is achieved by coating β-SiAlON:Eu2+ and NaZnF3:Mn4+ on an InGaN chip, indicating the potential use of the Mn4+ fluoroperovskite as a colour converter for display backlight application. [ABSTRACT FROM AUTHOR]

Three bismuth(III) bromide hybrids based on 2,2′-bipyridyl-1,1′-dioxide (bp2do) were obtained by a solvothermal method, namely Bi2Br6(bp2do)2 (1), Bi2Br6(bp2do)2·0.5CH3CN (2), and [PP14][BiBr4(bp2do)] (3, PP14 = 1-butyl-1-methylpiperidinium). 1 features a centrosymmetric [Bi2Br6O4] dimer, in which two identical [BiBr4O2] octahedra edge-share two Br atoms; 2 contains a [Bi2Br6O4] dinuclear unit with a unique configuration, in which a [BiBr4O2] octahedron face-shares one Br and two O atoms with a [BiBr3O4] pentagonal-bipyramid. Moreover, the metal–ligand linking mode adopted in 2 has not been reported before. The choice of organic solvents could induce different Bi–Br–bp2do geometries with a dimer in 1 and a dinuclear unit in 2. Introduction of ionic liquid cations resulted in the ionic compound 3 featuring a mononuclear [BiBr4(bp2do)] unit. A more rigid environment with more hydrogen bonds leads to visible green phosphorescence with long lifetime for 3 under UV light. The three compounds possess similar phosphorescence peaks at 77 K, which originates from inorganic-to-organic charge transfer (IOCT) as confirmed by density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

Five new salts of the 3,4-dicyano-2-(dicyanomethylene)-5-methyl-6-phenyl-2H-pyridin-1-ide anion (TCPy−) with lithium, sodium, potassium, rubidium and cesium cations were synthesized and structurally characterized by a single-crystal X-ray diffraction method. The solid state photoluminescence characteristics of the prepared salts were studied. The crystallographic features of the crystal packing which are responsible for the emission band position were investigated. Quantum-chemical calculations were carried out to explain the correlation between emission maxima and the crystal structure. [ABSTRACT FROM AUTHOR]

A hexagonal prismatic Cu6S6 cluster exhibits excellent near-infrared fluorescence properties due to its short Cu–Cu bonds, however, the construction of Cu6S6 cluster-based compounds with extended structures is still a challenge. Here, four new Cu6S6 cluster-based coordination compounds, formulated as Cu3(pymt)3 (1), {(CuCN)2[Cu3(mpymt)3]}n (2), {(CuSCN)[Cu3(mpymt)3]}n (3) and {(CuCN)2[Cu3(dmpymt)3]·CH3CN}n (4) (Hpymt = pyrimidine-2-thiolate, Hmpymt = 4-methyl-pyrimidine-2-thione and Hdmpymt = 4,6-dimethylpyrimidine-2-thione), have been synthesized through the reactions of mercaptopyrimidine derivatives and CuCN or CuSCN under solvo-thermal conditions and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, IR spectroscopy, elemental analysis, and thermal gravimetric analysis. Single-crystal X-ray diffraction analysis reveals that compound 1 is a zero-dimensional Cu6(pymt)6 molecule containing a distorted pseudo-hexagonal prismatic Cu6S6 core. Compounds 2 and 4 with isomorphic frameworks but different organic linkers show a rare three-dimensional framework with nor topology constructed from Cu6(mpymt)6 units and one-dimensional chiral [Cu(CN)]n chains; compared with compound 2, a more hydrophobic one-dimensional channel in compound 4 is observed due to the increase of the methyl groups on the pyrimidine ligand, in which acetonitrile molecules are filled in the channels of compound 4. Compound 3 shows a rare two-dimensional layer constructed from Cu6(mpymt)6 units and one-dimensional puckered (CuSCN)n chains. For the first time, Cu6S6 clusters are connected to one-dimensional inorganic CuCN (or CuSCN) chains through mercaptopyrimidine derivatives to obtain extended arrays in compounds 2–4. The crystals of compounds 1–4 in the solid state all show apparent red light emission. Compound 4 shows sensitive luminescence quenching response to nitrobenzene (NB), and the corresponding quenching constant (Ksv) and detection limit are 2.06 × 103 M−1 and 9.27 ppm, respectively. This study provides a new strategy to construct Cu6S6 cluster-based coordination polymers that have great potential in various applications such as luminescence sensing. [ABSTRACT FROM AUTHOR]

Mg–CaCO3:Eu3+ phosphors with various initial magnesium ion concentrations were successfully synthesized by a simple carbonation method without using any surfactant, catalyst, or template. It was shown that the different contents of magnesium ions in calcite play a crucial role in the morphology, structure, and luminescence properties. The morphologies of Mg–CaCO3:Eu3+ phosphors could be varied from spindle, dendritic, coral-like, and micron-flower-like to finally club-like by adjusting the initial magnesium ion mole percentage. The modified titration experiment indicated that not all magnesium ions had lattice substitutions. In addition, the photoluminescent properties and lifetimes of Eu3+ ions changed with the morphological and structural changes of the Mg–CaCO3:Eu3+ crystal, which was analyzed by Judd–Ofelt theory. Furthermore, temperature was also found to be a significant factor in the variation of the properties of Mg–CaCO3:Eu3+ phosphors. Finally, a crystal structure ball-and-stick model of Mg–CaCO3:Eu3+ phosphors was built and the possible mechanism of action was analyzed. This study provides an idea for the preparation of new hetero-ion phosphors. [ABSTRACT FROM AUTHOR]

By employing a triazole–pyridine-containing ligand, two novel coordination polymers with Ag(I) clusters exhibiting different architectures have been successfully constructed. Structural analysis indicates that diverse coordination modes of the N-donor linker are responsible for the network difference for these two compounds, affording an isolated cluster for 1 and a 2D framework for 2, respectively. Compound 1 features a butterfly-shaped [Ag8(bptp)4(H2O)2] cluster wherein strong argentophilic interactions could be observed. The linkage of Ag(I) with N and I centers gives rise to a tetranuclear building unit [Ag4(bptp)3I] in 2, which is further extended to a 2D network with the assistance of the N-donor linkers. The syntheses and crystal structures have been investigated. Solid-state photoluminescence emissions as well as luminescence lifetimes of 1 and 2 have also been studied. Moreover, temperature-dependent luminescence tests show that an excellent linear relationship between temperature and emission intensity in the ranges of 77–298 K and 77–200 K could be observed for compounds 1 and 2, respectively. The wide temperature sensing range especially for 1 implies that they could act as promising ratiometric fluorescence molecular thermometers. [ABSTRACT FROM AUTHOR]

A series of 12 new metal–organic frameworks based on lanthanide cations (Ln = Nd, Sm–Dy), octahedral cluster anions [Re6S8(CN)6]4− or [Re6Se8(CN)6]4− and adipamide (adp) were synthesized under mild conditions in aqueous ethanol solutions. Compounds of the general composition Cs[Ln(adp)2{Re6Q8(CN)6}]·3H2O (Ln = Nd, Sm–Dy; Q = S or Se) crystallize in the hexagonal space group P6422. Despite the presence of solvate H2O molecules in structure cavities, the crystal structures revealed that the coordination environment of lanthanide cations in these 3D polymers did not contain H2O ligands. This rare feature is attributed to the combination of a bulk cluster anion and flexible adp molecules, which occupy the lanthanide coordination sphere to yield a stable lanthanide-based building block. This assumption was confirmed by synthesis of a second crystalline modification of the compound Cs[Nd(adp)2{Re6S8(CN)6}]·3H2O (orthorhombic space group Cccm). Luminescence studies evidence the presence of the typical red luminescence of hexarhenium cluster complexes and the absence of observable luminescence of lanthanide cations for all the compounds except the Nd derivatives. Magnetic data indicate very weak antiferromagnetic exchange interactions between paramagnetic Ln3+ centers. [ABSTRACT FROM AUTHOR]

The development of novel white-light-emission phosphors is of great importance for applications in lighting and display fields. Trivalent Dy3+ is widely used as a potential luminescence center for white-light emission. However, Dy3+-doped phosphors often suffer a poor yellow to blue ratio due to the deficiency of its 4F9/2 → 6H15/2 transition, low luminescence efficiency, and unsatisfactory thermal stability. The importance of the present research work is that we have achieved a tunable white light in a single phased stannate phosphor Sr3Al10SnO20:Dy3+ with robust thermal stability. The crystal structure, phase purity, and chemical composition were investigated via X-ray diffraction Rietveld structure refinement, scanning electron microscopy, and energy dispersive spectrometry. The luminescence spectra indicated that Sr3Al10SnO20:Dy3+ not only exhibited characteristic 4F9/2 → 6HJ/2 (J=11, 13, and 15) inherent transition emissions of Dy3+, but also showed an abnormal blue band emission, which was identified through X-ray photoelectric spectroscopy as the T1 → S0 transitions of Sn2+, resulting from the valence variation of Sn4+. The efficient energy transfer from Sn2+ to Dy3+ was also confirmed and the transfer efficiency was calculated. Owing to the valence-variation-induced emission of Sn2+, a tunable white light could be realized from a cool to warm white light region, with Commission Internationale de l'Eclairage coordinates and a correlative color temperature varying from (0.277, 0.333) and 8634 K to (0.353, 0.404) and 4913 K, respectively. The luminescent and defects formation mechanism as well as the luminescence kinetics were further investigated. Moreover, Sr3Al10SnO20:Dy3+ had a high quantum efficiency (∼34.6%) and a super-stable thermal stability behavior (82.5% at 240 °C of the initial integral emission intensity at 30 °C) with a large activation energy (ΔE ∼ 0.1654 eV). Finally, a charge-compensation test was performed to further verify the effect of defects on the luminescence property and the related mechanism was discussed. The current work provides a novel method to achieve tunable white-light emission in Dy3+ single-doped phosphors and the related mechanism is effectual for other rare earths for potential applications in lighting and display fields. [ABSTRACT FROM AUTHOR]

A new series of BaY2−xEuxGe3O10 (x = 0.1–0.8) trigermanates has been synthesized using the solid-state reaction method. A powder XRD study has revealed that the compounds crystallize in the monoclinic system, space group P21/m, Z = 2. The crystal lattice consists of distorted Y/EuO6 octahedra, trigermanate [Ge3O10]8− groups and Ba atoms located in eight-fold coordinated irregular sites. Under UV and 465 nm light excitation, the samples exhibit reddish-orange emission corresponding to the characteristic 5D0 → 7FJ transitions in Eu3+ ions. Concentration dependence study has shown that the powders with europium content x = 0.4–0.6 possess the highest luminescence intensity under 393 nm and 465 nm excitation. It has also been revealed that the predominant mechanism causing concentration quenching in the BaY2−xEuxGe3O10 series is due to multipolar interactions. The investigations on colour characteristics, quantum efficiency and thermal stability performance of BaY2−xEuxGe3O10 phosphors were carried out for the feasibility study of their practical application. The results indicate that BaY2−xEuxGe3O10 can be considered as a promising material for blue-excited phosphor-converted LEDs. [ABSTRACT FROM AUTHOR]

Three lanthanide polymers {[Ln(TMCA)(DEF)(H2O)]·(CH3CN)}n (Ln = Eu 1; Tb 2; Gd 3; H3TMCA = 4′,4′,4′-[(trimethylamino)]-tris[(1,1′-biphenyl)-2-carboxylic acid]) were synthesized under solvothermal conditions. The coordination polymers were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis and single-crystal X-ray diffraction. Single crystal X-ray diffraction analyses showed that the complexes 1, 2 and 3 are isostructural 2D coordination networks with a point symbol of {44·62}. Complexes 1 and 2 exhibit red and green emission, assigned to the 5D0 → 7FJ (J = 0–4) transitions of the Eu3+ ion and 5D4 → 7FJ (J = 6–2) transitions of the Tb3+ ion, respectively. The luminescence explorations reveal that the Eu-MOF possesses favorable selectivity and sensitivity for testing Fe3+ in CH3OH solutions. Additionally, color tuning was easily achieved by varying the europium : terbium metal ratios in the reaction mixtures. [ABSTRACT FROM AUTHOR]

Four novel coordination polymers (CPs), {[Zn2(tbta)(phen)(OH)]·4H2O}n (1), {[Zn4(tbta)2(bpy)(OH)2(H2O)2]·7H2O}n (2), {[Cu2(tbta)(phen)(OH)]·4H2O}n (3) and [Cu2(tbta)(phen)2(OH)]n (4) (H3tbta = 1-(triazol-1-yl)-2,4,6-benzene tricarboxylic acid; bpy = 4,4′-bipyridine; phen = 1,10-phenanthroline), were synthesized and characterized by elemental analyses, FT-IR spectroscopy, and single-crystal X-ray diffraction analyses. CP 1 shows a 2D bilayer network structure based on binuclear ZnII units and (tbta)3− ligands, which are arranged in an [ABAB⋯] alternation to form 3D supramolecular structures through π⋯π stacking interactions and hydrogen bonding interactions. Noticeably, CP 2 forms a 3D network structure based on binuclear ZnII units and (tbta)3− and bpy ligands. Interestingly, the lattice H2O molecules are joined by strong hydrogen bond interactions generating (H2O)10 clusters, which make contact with the 2D network to form a 3D supramolecular structure. CPs 3 and 4 have a 2D network structure. In particular, the (tbta)3− ligands in 1–4 adopt four different coordination modes. The thermal stabilities, XRD, UV, and photoluminescence properties of CPs 1–4 were also studied. Remarkably, CP 1 is a highly selective and sensitive bifunctional luminescent sensor towards Cu2+ and Cr2O72− ions. Moreover, CPs 3 and 4 exhibit photocatalytic activities for degradation of dyes (MB/MO) under UV light irradiation. [ABSTRACT FROM AUTHOR]

The lanthanide binding ability of a macrocyclic ligand H6L2 comprising two bis(iminomethyl)phenol and two calix[4]arene units has been studied. H6L2 is a ditopic ligand which provides dinuclear neutral complexes of composition [Ln2(L2)(MeOH)2] (Ln = La (1), Eu (2), Tb (3), and Yb (4)) in very good yield. X-ray crystal structure analyses for 2 and 3 show that (L2)6− accommodates two seven coordinated lanthanide ions in a distorted monocapped trigonal prismatic/octahedral coordination environment. UV-vis spectroscopic titrations performed with La3+, Eu3+, Tb3+ and Yb3+ ions in mixed MeOH/CH2Cl2 solution (I = 0.01 M NBu4PF6) reveal that a 2 : 1 (metal : ligand) stoichiometry is present in solution, with log K11 and K21 values ranging from 5.25 to 6.64. The ratio α = K11/K21 of the stepwise formation constants for the mononuclear (L2 + M = ML2, log K11) and the dinuclear complexes (ML2 + M = M2L2, log K21) was found to be invariably smaller than unity indicating that the binding of the first Ln3+ ion augments the binding of the second Ln3+ ion. The present complexes are less luminescent than other seven-coordinated Eu and Tb complexes, which can be traced to vibrational relaxation of excited EuIII and TbIII states by the coligated MeOH and H2O molecules and/or low-lying ligand-to-metal charge-transfer (LMCT) states. [ABSTRACT FROM AUTHOR]

To explore different photoluminescence phenomenon of Ti4+ ions, a rare-earth-free self-activated phosphor Li2TiSiO5 was synthesized and studied in detail. The crystal structure, photoluminescence properties and thermal quenching of Li2TiSiO5 were discussed. The crystal structure has been investigated by Rietveld refinement, and this indicates that there is a special kind of TiO5 square pyramids in this structure. Under 245 nm excitation, Li2TiSiO5 emits white light ranging from 400 to 780 nm with CIE coordinates of (0.388, 0.441), which is due to the existence of isolated TiO5 square pyramids and TiO6 octahedra in the disordered non-crystalline powder, which is also proved by the time-resolved photoluminescence. The abnormal serious thermal quenching is ascribed to thermal ionization. The study of Li2TiSiO5 broadens the research of rare-earth-free Ti-doped oxides due to its self-activated luminescence and the realization of white light emission in a single host. [ABSTRACT FROM AUTHOR]

Four D–A type Zn(II) coordination complexes, [Zn(C29H29N3O2)·(CH3OH)]·(CH3OH) (1), Zn2(C74H90N6O4)·(CH3OH) (2), [Zn(C30H28N4O2)·(CH3OH)]·(CH3OH) (3) and [Zn(C38H44N4O2)·(C2H5OH)]·(C2H5OH) (4), were designed, synthesized, and studied. Their fluorescence properties in the solid state and in THF solution were comprehensively analysed based on their single-crystal structures. The results showed that the red-shift of fluorescence emission from complexes 1 to 4 was successfully achieved via the strategy of enhancing intramolecular charge transfer (ICT) effects by increasing the number of electron-pulling and pushing groups gradually. Meanwhile, because of the fluorescence recognition abilities of these four complexes towards iodide anions in THF, they could be regarded as potential fluorescent sensors for I− in this organic solution in the future. [ABSTRACT FROM AUTHOR]

Four coordination polymers, namely, {[Co(cpnc)(bpbenz)]}n (1), {[Co(cpnc)(bide)2]}n (2), {[Co(cpnc)(bide) (H2O)1/2]·H2O}n (3), and {[Cd(cpnc)(bib)1/2(H2O)2]}n (4) (H2cpnc = 6-(4-carboxyphenyl)nicotinic acid, bpbenz = 1,4-bis(4-pyridyl)benzene, bide = 4,4′-bis(imidazolyl)diphenyl ether, and bib = 1,4-bis(1-imidazoly)benzene) have been solvothermally synthesized and characterized by powder X-ray diffraction, elemental analysis, and infrared spectroscopy. Structural analysis reveals that compound 1 consists of a 3D 3-fold interpenetrated framework with pcu topology. Compounds 2 and 3 have been synthesized by one-pot reactions. Compound 2 comprises 2D layers, while compound 3 comprises 1D chains. Compound 4 consists of 2D layers constructed from mixed ligands. In addition, the photocatalytic activities of 1–3 under UV light toward methyl orange (MO), rhodamine B (RB), methyl blue (MB), neutral red (NR), methylene blue (MEB), and safranine T (ST) with H2O2 are investigated in aqueous solutions. The results suggested that the photocatalytic efficiency of 1 for MO was 100% in one hour and that of 2 for ST was 90% in two hours; furthermore, the photocatalytic efficiencies of 3 for MO and ST were found to be 100% and 92% in one hour, respectively. The photoluminescence titration experiments demonstrate that 4 is an excellent multifunctional probe for metal ions (Fe3+ and Cu2+) and anions (Cr2O72− and CO32−). [ABSTRACT FROM AUTHOR]

Red emitters based on CaAl12O19:Mn4+ have been attracting extensive attention due to their advantages of being rare-earth-free and chemically stable. However, their relatively low luminescence efficiencies will seriously hinder their application in light-emitting diodes (LEDs). In this regard, the promising red phosphors of CaAl12O19:Mn4+ were synthesized with enhanced luminous efficiency by introducing the coexisting phase of MgAl2O4. Importantly, an approximately 5 times enhancement of integrated intensity in the emission spectrum was observed for the phosphor with the coexisting phase compared to that with a single phase. Their crystal structures, morphologies and photoluminescence properties and the mechanism of improved luminescence were systematically investigated. Upon exciting them by using near-ultraviolet or blue LEDs, an efficient red emission was achieved with a maximum peak at ∼658 nm. In order to evaluate their potential application, a warm white LED and a plant growth LED were fabricated by using the prepared phosphors in combination with YAG:Ce3+ and InGaN-based blue chips. [ABSTRACT FROM AUTHOR]

Room temperature phosphorescence by metal-free chromophores is quite a rare phenomenon. Hexasulfurated benzene-cored molecules with phenyl substituents, hereafter named asterisks, display bright green phosphorescence in the solid state at room temperature, while they are not luminescent in solution, because of fast non-radiative decay of the lowest excited state. Some of these asterisks are also among the most phosphorescent compounds. Following a search for structure–property relationships, we report here the synthesis, characterization, crystal structure and optical properties of three pentasulfurated benzene-cored asterisks, carrying at the sixth position of the benzene core a cyano (A5CN), a carboxaldehyde (A5CHO), or a vinyl group (A5CC). The most luminescent compound is A5CN, displaying an intense orange phosphorescence in the solid state. Our actual aim is to try and correlate the optical properties with the crystal structure in this series of compounds. [ABSTRACT FROM AUTHOR]

Using a mixed ligand synthesis strategy involving semi-rigid 4-(4-carboxyphenoxy)-isophthalic acid (cphtH3), oxalate (ox) as a mixed linker and 1,10-phenanthroline (phen) as an ancillary terminal ligand, a series of highly stable metal coordination frameworks, Ln-MOFs, [Ln(cphtH)phen(ox)0.5]n·mH2O (Ln = Sm 1, Eu 2, Gd 3, Tb 4 and Dy 5), were synthesized. They are isostructural 3D coordination networks of interlinked left- and right-handed helices based on [LnO7N2] connections. The Brunauer–Emmett–Teller (BET) surface area was 3.3020 m2 g−1 (Langmuir surface area: 3.6940 m2 g−1). They are chemically stable in common solvents and are stable in aqueous solutions from pH = 4 to 9. Complexes 1 and 5 are dual-emissive materials exhibiting a broad emission band from the π*–π transition of the organic linker and narrow emission peaks, the 4G5/2 → 6HJ (J = 5/2, 7/2, and 9/2) transitions of the Sm3+ ion for 1 and 4F9/2 → 6HJ (J = 15/2 and 13/2) transitions of the Dy3+ ion for 5. Complexes 2 and 4 exhibit red and green emission, assigned to the 5D0 → 7FJ (J = 1–2) transitions of the Eu3+ ion and 5D4 → 7FJ (J = 6–3) transitions of the Tb3+ ion, respectively. The maximum excitation wavelengths are 356, 358, 360 and 350 nm for 1, 2, 3 and 4, respectively, which are in the near-visible radiation region (350 nm < λex < 420 nm). The Sm-MOF (1) displays a single component white light based on its dual-emission. The primary focus of this study is to examine the fluorescence properties of Eu-MOF (2) as it showed excellent luminescence in solvent as well as aqueous solutions over a wide pH range (pH = 4–9). Based on the luminescence quenching of the Eu-MOF, the detection of quercetin in water and Fe3+ ions in several solvent systems was realized at a long maximum excitation wavelength of 358 nm. [ABSTRACT FROM AUTHOR]

White light-emitting diodes (WLEDs) have been considered as the next generation lighting technology due to their advantages such as high efficiency and environmental friendliness. However, current mainstream WLEDs, which are based on blue chips and the Y3Al5O12:Ce3+ yellow phosphor, suffer from the problem of low color rendering index (CRI). To solve this problem, a yellowish-green phosphor Ca1.5Y1.5Al3.5Si1.5O12:Ce3+ (CYAS:Ce3+) based on the garnet structure has been designed in this study. Its crystal structure, band structure, and luminescence properties have been investigated in detail. CYAS:Ce3+ exhibits efficient and thermal-stable yellowish-green emission. The 5d centroid shift and crystal splitting of the Ce3+ ion in CYAS have been analyzed together with the structure. Moreover, good warm white light with a low correlated color temperature (3210 K), high color rendering index (85.1) and luminous efficacy (88.5 lm W−1) has been obtained by combining CYAS:Ce3+ and the red phosphor CaAlSiN3:Eu2+ with a blue LED chip. [ABSTRACT FROM AUTHOR]

Structures of three polymorphs of 1-acetylpyrene were determined using single-crystal X-ray diffraction and their solid state luminescence was investigated. While the formerly known 1AP-α polymorph, with its herringbone packing motif, is proved to be non-luminescent, the newly discovered polymorphs β and γ, with crystal structures based on π⋯π-dimers, luminesce intensely in blue and green accordingly. This discovery contradicts a possibility of systematic control over the packing of pyrene units in crystals by progressive addition of acetyl groups, formerly claimed for n-acetyl-pyrenes. [ABSTRACT FROM AUTHOR]

Novel three dimensional (3D) isostructural lead(II) halide coordination polymers [Pb(INO)X]n (X = Cl (1), Br (2), I (3); INO = isonicotinic acid N-oxide) have been synthesized via a branched-tube method. The compounds have been characterized by IR spectroscopy and powder X-ray diffraction (PXRD) analysis and their crystalline structures have been determined by single-crystal X-ray diffraction. Isostructural compounds 1–3 crystallize in the orthorhombic crystal system with the Pbcn space group. Two N-oxide groups of INO anions connect to a pair of adjacent Pb(II) ions to create a one-dimensional (1D) infinite zigzag chain and carboxylate groups connect the lead(II) ions resulting in [Pb2O2] units. Nanoplates of compounds 1–3 have also been synthesized under ultrasonic irradiation and characterized by IR spectroscopy, SEM and PXRD. Moreover, compounds 1–3 exhibited reversible solid-state crystal-to-crystal transformation under mechanochemical reactions. The thermal stability of these crystalline materials has been presented. The fluorescence features of these compounds have also been studied in solution for bulk and nanostructures at ambient temperature. [ABSTRACT FROM AUTHOR]

Finding new luminescent materials is always a meaningful goal in the field of photoelectricity studies. Herein, a new diphosphate compound Ba2LiGa(P2O7)2 (BLGP) was prepared using a high-temperature flux method. It displays an anionic chain structure of [LiGa(P2O7)2]∞, constructed from P2O7, LiO5 and GaO6 polyhedra. The Ba2+ ions are distributed in the voids between the [LiGa(P2O7)2]∞ chains, bonding them and maintaining charge balance. To test its potential as a luminescent host, Eu3+ doped phosphors BLGP:xEu3+ (x = 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) were synthesized and studied in detail. Upon 394 nm light irradiation, BLGP:xEu3+ showed bright orange emission with a dominant peak at 595 nm due to the 5D0 → 7F1 transition of Eu3+. The optimal doping amount of Eu3+ is 0.20, and the internal quantum efficiency of the phosphor B1.8LGP:0.2Eu3+ was determined to be 67%. The temperature quenching behavior of B1.8LGP:0.2Eu3+ was studied, suggesting that the photoluminescence (PL) intensity decreased to about 50% at 450 K due to thermal quenching. All these features show that this compound is a good luminescent host material for Eu3+ activators. [ABSTRACT FROM AUTHOR]

Reactions of bis[5-(2-pyridyl)-1,2,4-triazol-3-yl]alkanes (alkane spacers = –CH2– in L2, –C3H6– in L3, –C4H8– in L4) with M(ii)A2 salts (M = Ni, Co, Fe) resulted in the preparation of five series of mononuclear ([M(L2)(H2O)2]2+, 1a–c) or binuclear ([M2(L3)2(H2O)4]4+, 2a–c; ([M2(L4)2(H2O)4]4+, 3a–c, [M2(L3)2(μ-ox)]2+, 4a–c; [M2(L4)2(μ-ox)]2+, 5a–c) complexes. The crystal structures of ten complexes were determined by single-crystal X-ray crystallography. Magnetic properties of the compounds were characterized by SQUID magnetometry and were analyzed by fitting on a spin Hamiltonian model. It was revealed that Fe(ii) and Co(ii) compounds exhibit non-negligible anisotropy and in the case of 2a–c and 3a–c complexes weak ferromagnetic interactions between the metal centers were observed. In the case of complexes containing an {M2(μ-ox)}2+ core strong antiferromagnetic interactions were observed within the dimer. Remarkably, solid state luminescence of Co(ii) and Fe(ii) complexes (1b, 2b, 3b and 1c, 2c, 3c) was observed. [ABSTRACT FROM AUTHOR]

A novel silicate-based phosphor Ba5SiO4Cl6:Eu2+ (BSOC:Eu2+) was successfully designed and investigated through the solid-state method. The crystal structure, band structure, photoluminescence and cathodoluminescence characteristics were investigated in detail. Under excitation at 345 nm, a narrow blue emission band with a peak at 440 nm (FWHM ∼ 32 nm) could be observed. Moreover, BSOC:Eu2+ showed higher color purity when compared with a commercial BAM phosphor. Under sustained low-voltage electron-beam excitation, the BSOC:Eu2+ phosphor exhibited blue emission with distinguished degradation resistance and perfect colour stability. By combining the BSOC:Eu2+ blue phosphor with green and red phosphors and an n-UV chip, a pc-WLED with a high color rendering index and low correlated color temperature was obtained. The results show that the BSOC:Eu2+ phosphor has wide application prospects in n-UV LED applications and FED devices. [ABSTRACT FROM AUTHOR]

Yb3+–Er3+ and Yb3+–Ho3+ co-doped Ba3Lu2Zn5O11 phosphors were successfully obtained. The structure of the as-synthesized phosphor was determined by Rietveld refinement. The up-conversion (UC) spectra of Ba3Lu2Zn5O11:Yb3+,Er3+ exhibits two prominent emission bands centered at 560 and 663 nm, which originate from the 2H11/2/4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3+, respectively. Ba3Lu2Zn5O11:Yb3+,Ho3+ revealed a bright green emission at around 553 nm and negligible red emission peaking at 660 nm, which were assigned to the 5F4/5S2→5I8 and 5F5→5I8 transitions of Ho3+, respectively. The up-conversion luminescence of the samples was studied as a function of the concentration of the dopants. The origin of the UC mechanism is discussed in detail by analyzing energy-level diagrams, the dependence of the UC emission intensity on pump power, and the lifetimes. The results indicate that the Ba3Lu2Zn5O11:Yb3+,Er3+/Ho3+ phosphors are excellent up-conversion emitters and have potential applications in display and illumination technologies. [ABSTRACT FROM AUTHOR]

New composite functional crystals of Tm3+:Ca3NbGa3Si2O14 (Tm3+:CNGS) were successfully grown by the Czochralski (CZ) method. The structural, thermal and spectral properties of Tm3+:CNGS crystals were investigated. The laser output of a Tm3+:CNGS crystal in the 2 μm band was studied for the first time. The results showed that Tm3+:CNGS achieved a maximum output of 740 mW at a pump power of 5 W, and the slope efficiency and light-to-light conversion efficiency reached 17.07% and 14%, respectively. The thermal properties are presented, and the coefficient of linear thermal expansion of Tm3+:CNGS increased with respect to that of a pure CNGS crystal in the Z-axis direction, which may have been due to a change in the bulk density of the oxygen dodecahedron in the X-axis direction after partial replacement of the rare earth ions. In addition, the specific heat, thermal diffusivity, and thermal conductivity of Tm3+:CNGS slightly increased in comparison with those of the undoped CNGS crystal. The absorption spectra of Tm3+:CNGS had a strong peak at 793 nm, and its absorption cross-section was 5.01 × 10−21 cm2. The fluorescence spectra at room temperature had a full width at half maximum (FWHM) of 164 nm and a peak wavelength of 1888 nm, and the lifetime of the 3F4 upper energy level of the laser was 2.345 ms. Its good thermal properties, large emission linewidth, and ease of growth indicate that a Tm3+:CNGS single crystal could have the potential to be a good laser gain medium. [ABSTRACT FROM AUTHOR]

In this study, two metal–viologen complexes, formulated as [Cd1.5(H2L)0.5(Cl)3(CH3OH)]n (1) and [Eu2(L)(NO3)4(HOCH2CH2OH)2]n (2), were constructed by a tetracarboxylate anchored bipyridinium-based ligand 1,1′-bis(3,5-dicarboxybenzyl)-4,4′-bipyridinium dichloride (H4L·Cl2). Single-crystal X-ray analyses revealed that complex 1 featured a 2D-layered structure, while complex 2 showed a 1D “ladder-like” chain structure. The difference in the central metal ions, anions, solvent molecules, deprotonation degree of the tetracarboxylate ligand, coordination modes and conformations of the ligand have a great influence on the final structure. As expected, incorporation of the viologen moiety to the frameworks led to the predefined photochromism: when samples 1 and 2 were exposed to UV-visible light, a reversible color change from light yellow to blue/dark blue occurred. Moreover, complex 2 exhibited the characteristic emission of Eu(iii) ion in the visible region, and it also displayed an interesting reversible tunable photo-induced luminescence switching behavior: under the irradiation of UV-vis light, the luminescence emission intensity of complex 2 gradually decreased and reached 15% of the starting value after 8 min. These results may not only help to further understand the structure–photoresponse relationships of viologen-based MOFs, but also help to guide the design and synthesis of luminescent materials with photo-modulated switching ability. [ABSTRACT FROM AUTHOR]

In this work, in order to meet the application of near-infrared phosphor-converted light emitting diodes (pc-LEDs), an ultra-broadband emission phosphor, LiScGeO4:Cr, was synthesized. Its FWHM reaches 335 nm, and its emission spectrum ranges from 800 nm to 1650 nm, which almost covers the entire near-infrared second window (NIR-II). The broadband emission is thought to be caused by the 4T2 → 4A2 transition of the Cr3+ ion. This transition occurs due to the olivine structure of the crystal, which causes the Cr3+ ions to inhabit a low-symmetric crystal field, and the crystal field strength is very weak. NIR pc-LEDs were fabricated by combining a 460 nm blue LED with this phosphor, which penetrates 4 cm thick beef. The results indicate that there may be a potential application for this phosphor in the field of biological tissue penetration and non-destructive testing. [ABSTRACT FROM AUTHOR]

A novel green-yellow emitting Ca1.5Mg0.5Si1−xLixO4−δ:Ce3+ phosphor with high quantum efficiency and thermal stability was discovered for applications in near ultraviolet pumped white light-emitting diodes. Its crystal structure was determined with a single-particle diagnosis approach. The Si sites in the SiO4 tetrahedra are reported for the first time to accommodate Li+ ions. This substitution, confirmed by 6Li solid-state NMR and T.O.F. neutron powder diffraction, causes a disordered occupation of Ca/Mg in the Ca3MgSi2O8 host and favors a phase transformation at ∼330 °C, which results in the formation of the novel phosphor. The produced phosphor was efficiently excited by near UV light peaking at 365 and 410 nm and produced broad green-yellow emission with peaks at 500 and 560 nm, respectively. Its quantum efficiency reached 88.4% (internal) and 55.7% (external) under excitation at 365 nm, and 80.5% (internal) and 42.7% (external) under excitation at 410 nm, while the decrease of luminescence intensity at 200 °C was small (∼26%). A WLED lamp with a high color rendering index of Ra = 92.8 was produced with the combination of a 365 nm emitting chip with blue emitting BaMgAl10O17:Eu2+, green-yellow emitting CMSL:0.01Ce, and red emitting Sr2Si5N8:Eu2+ phosphors. [ABSTRACT FROM AUTHOR]

Two 12-metal Zn–Ln nanoclusters [Zn8Ln4L8(OAc)8](OH)4 (Ln = Sm (1) and Nd (2)) were prepared using a long-chain Schiff base ligand with a flexible (CH2)3O(CH2)2O(CH2)3 backbone. These two Zn–Ln clusters possess interesting rectangular structures. The long-chain Schiff base ligand adopts a “linear” configuration in the structures, resulting in the large sizes of 1 and 2 (about 9 × 19 × 28 Å). Chromogenic Zn/L components in the clusters can act as efficient sensitizers for lanthanide luminescence, and 1 and 2 exhibit emission from Sm3+ and Nd3+, respectively. Their visible and NIR luminescence properties were investigated. [ABSTRACT FROM AUTHOR]