Sharp-Line Near-Infrared Emission from Tetrahedron-Occupied Ni2+ in Ca2GeO4.

As far as we are concerned, the phenomenon of Ni2+ luminescence in tetrahedral coordination has not been reported. For the first time, a new NIR phosphor Ca2GeO4:Ni2+ is developed in this work. It is found that the NIR emission from this phosphor is a sharp peak attributed to the unusual Ni2+-occupied GeO4 site in the lattice, instead of the conventional broadband luminescence of Ni2+ in the octahedrally coordinated site. Crystal-field analysis has been applied, and the parameters Dq, B, and Δ are calculated to reveal the relationship between the emission profile and the crystal field strength. The optimal Ni2+ doping concentration is found to be 1%. Ca2GeO4:Ni2+ provides an efficient sharp-line (fwhm = 16 nm) emission centered at 1164 nm which originates from the 1T2 → 3T1 transition with an internal quantum efficiency of 23.1% and a decay lifetime of about 300 µs. This work could provide some new insights to explore novel NIR luminescent materials based on transition-metal elements.

Achieving Ultra-Wideband NIR-II Emission in Cr3+-Doped Li(Sc,In)(Si,Ge)O4 Phosphors Based on Host Composition Engineering.

Realizing ultra-wideband and tunable near-infrared (NIR) emission remains a great challenge in NIR phosphor development. The luminescence of most reported NIR phosphors exhibits a peak wavelength shorter than 1000 nm and the corresponding FWHM is <200 nm. Here, a series of Cr3+-activated Li(Sc,In)(Si,Ge)O4 phosphors with ultra-wideband and tunable NIR-II emission are successfully developed based on the host composition engineering strategy. Significant spectral engineering in the NIR-II region is achieved with a peak wavelength changing from 1110 to 1253 nm. The olivine host structure could provide Cr3+ activator a highly distorted octahedral site with very weak crystal field strength, which results in NIR-II ultra-wideband emission with FWHM > 300 nm. A detailed discussion on the relationship between structural variation, crystal field splitting, and NIR luminescence has been applied. As far as we know, it is the first report about Cr3+ NIR luminescence engineering in such a long wavelength and wide range. The application of these NIR-II phosphors is demonstrated in intensity-based luminescent thermometry with a relative sensitivity of >2.0% K-1 in the physiological temperature range.

Ultrahigh-Energy-Transfer Efficiency and Efficient Mn2+ Red Emission Realized by Structural Confinement in Ca9LiMn(PO4)7:Eu2+,Tb3+ Phosphor.

Structural confinement on Eu2+-Mn2+ optical centers is an effective strategy to boost Mn2+ red emission. On the basis of the Ca9LiMn(PO4)7 (CLMP) host with a compact Eu2+-Mn2+ distance of ∼3.5 Å, a pure and intense Mn2+ red emission without seeing Eu2+ emission is realized, indicating that an ultrahigh energy transfer (ET) could be induced by a structural confinement effect. It is found that the Mn2+ emission intensity and quantum efficiency could be further improved by a Tb3+ bridging effect, which offers extra energy levels to reduce the energetic mismatch between the excited states of Eu2+ and Mn2+. The optimal sample CLMP:0.02Eu2+,0.90Tb3+ shows a promising performance in terms of high color purity (93.9%), high quantum efficiency (QE = 51.2%), and good thermal stability (70% of the room-temperature value at 373 K). All of the results demonstrate that CLMP:Eu2+,Tb3+ phosphor is a promising red-light-emitting-diode phosphor, and the structural confinement effect should be developed as a general strategy to enhance the ET efficiency for a pure and efficient emission.

The effects of charge compensation on photoluminescence properties of a new green-emitting ZnB2O4:Tb3+ phosphor.

Charge compensation is an effective way to eliminate charge defects and improve the luminescent intensity of phosphors. In this paper, a new green-emitting phosphor ZnB(2)O(4):Tb(3+) was prepared by solid-state reaction at 750 °C. The effects of Tb(3+) doping content and charge compensators (Li(+), Na(+) or K(+)) on photoluminescence properties of ZnB(2)O(4):Tb(3+) were investigated. X-ray powder diffraction analysis confirms the sample has cubic structure of ZnB(2)O(4). The excitation and emission spectra indicate that this phosphor can be excited by near ultraviolet light at 378 nm, and exhibits bright green emission with the highest peak at 544 nm corresponding to the (5)D4 → (7)F5 transition of Tb(3+). The critical quenching concentration of Tb(3+) in ZnB(2)O(4) host is 8 mol%. The results of charge compensation show that the emission intensity can be improved by Na(+) and K(+). Specifically, K(+) is the optimal one for ZnB(2)O(4):Tb(3+).

Wide-band excited and deep-red sensitized Mn2+ emission from an NaSrSc(BO3)2:Eu2+,Mn2+ phosphor with vanished Eu2+ emission.

It is of great importance to develop new broadband red phosphors since they have possible applications like plant cultivation, indoor lighting and non-destructive sensing. Herein, we report a series of Eu2+, Mn2+ activated NaSrSc(BO3)2 phosphors via a conventional solid-state reaction route. It has been found that both Mn2+ and Eu2+ solo-doped NaSrSc(BO3)2 show weak or no luminescence, while Eu2+, Mn2+ co-doped NaSrSc(BO3)2 exhibits wide-band absorption and intense deep-red emission at 680 nm with color purity of 89%. Analysis of the absorption, excitation and emission spectra of Eu2+, Mn2+ solo- and co-doped NaSrSc(BO3)2 indicates that this deep-red broadband emission originates from Eu2+ sensitization of the octahedron Mn2+ 4T1-6A1 transition. It was found that the photoionization process led by energetic similarity of the host band-gap and the Eu2+ lowest 5d excited state was mainly responsible for the vanished luminescence of Eu2+. The values of internal quantum efficiency (IQE) and absorption efficiency (AE) for the optimal NSSO:0.007Eu2+,0.05Mn2+ sample are 24.5% and 61.8%, respectively. This work could provide new insights into exploring novel Mn-activated deep-red luminescent materials.

Broadband-excited and green-red tunable emission in Eu2+-sensitized Ca8MnTb(PO4)7 phosphors induced by structural-confined cascade energy transfer.

Novel green-red color-tunable Ca8(Mg,Mn)Tb(PO4)7:Eu2+ phosphors have been synthesized via the traditional solid-state method. Since Tb3+/Mn2+ ions are the parent ions in the lattice, the structural confinement occurs when the sensitizer Eu2+ is introduced into the Ca8(Mg,Mn)Tb(PO4)7:Eu2+ structure. The distance from Eu2+ to Tb3+/Mn2+ is confined in the 5 Å range, which induces a highly efficient energy transfer process. At Eu2+ 350 nm excitation, Ca8MgTb(PO4)7:Eu2+ shows dominant Tb3+ green emission with almost-vanished Eu2+ emission. Red emission is clearly observed as Mn2+ ions doping into Ca8MgTb(PO4)7:Eu2+, and color-tuning from green to red is realized by varying the Mn2+ contents. Eu2+-Tb3+-Mn2+ cascade energy transfer process is in effect due to short Eu2+-Tb3+/Mn2+ and Tb3+-Mn2+ distances, which is verified by PL and decay variations. Meanwhile, the Ca8(Mg,Mn)Tb(PO4)7:Eu2+ phosphor indicates good thermal stability and maintained the 45% emission level at 150 °C, which demonstrates their potential applications in white light LEDs.

High-efficient and pH-sensitive orange luminescence from silicon-doped carbon dots for information encryption and bio-imaging.

The exploration of carbon dots (CDs) with high quantum yield, facile synthesis path and satisfying output for their multiple applications remains a challenge. Thus, a silicon-doped orange-emitting carbon dots (O-CDs) is synthesized via a one-step hydrothermal method o-phenylenediamine and ethyl orthosilicate as raw materials. The O-CDs exhibits a bright and non-excitation-dependent emission peaking at 580 nm, and the corresponding quantum yield could be greatly boosted from 39.2 % to 64.1 % by silicon doping. The obtained O-CDs possess good biocompatibility and promising luminescence stability with varying solvents, ionic concentrations and temperatures. Its bio-imaging ability is performed by incubating zebrafish embryos with O-CDs aqueous solution, and clear in-vivo fluorescent images are obtained. Furthermore, due to its high-efficient and specific pH-sensitive emission with excellent dispersibility, the O-CDs can be used as a fluorescent ink for dual-model data encry/decryption in both hand-writing and stamp printing. Therefore, the as-prepared O-CDs show the potential as promising candidate for biomedical diagnosis, data encryption, and anti-counterfeiting.

Tunable photoluminescence and energy transfer of Sr9LiMg(PO4)7: Ce3+/Tb3+/Mn2+ phosphors.

The Ce3+/Tb3+/Mn2+ activated color-tunable phosphors Sr9LiMg(PO4)7 (SLMP) were prepared by solid-state reaction with post-annealing treatment. The structural, static and time-resolved luminescent properties are studied in detail. XRD pattern showed the pure trigonal phase of Sr9LiMg(PO4)7 at an annealing temperature of 1300 °C. Ce3+-doped SLMP phosphor exhibits near-ultraviolet emission with peak-wavelength at 380 nm. Efficient Ce3+-Tb3+/Mn2+ energy transfer process is demonstrated by luminescence spectrum and luminescence lifetimes of as-prepared samples. The emitting-color of SLMP: Ce3+/Tb3+/Mn2+ was tunable through changing Ce3+/Tb3+/Mn2+ ratio. Emission peak intensity of SLMP: Ce3+, Tb3+ phosphor shows good thermal stability with rising temperature. These results suggest its great potential as luminescent materials with good performance for UV-excitable applications.

A high-sensitive ratiometric luminescent thermometer based on dual-emission of carbon dots/Rhodamine B nanocomposite.

A core-shell nanocomposite based on carbon dots (CD)/Rhodamine B (RhB) is realized by a facile method. The composite particles show spherical shape with narrow size distribution, non-agglomeration and smooth surface. The as-obtained nanocomposite shows the characteristic dual-emission of thermal-stable CD blue emission and thermal-sensitive RhB red emission at a single excitation wavelength. The fluorescence intensity ratio (FIR) is found to have a good linear relationship (R2 > 0.993) with temperature, while the corresponding maximum absolute and relative sensitivity is 2.01% K-1 and 1.39% K-1 in range of 283-373 K. The research provides a simple approach to create novel dual-emitting nanocomposites for temperature sensing application in micron-scale and biological field.

Improving moisture stability of SrLiAl3N4:Eu2+ through phosphor-in-glass approach to realize its application in plant growing LED device.

Herein, we present a simple strategy to enhance the stability of water-sensitive SrLiAl3N4:Eu2+ phosphor through embedding the phosphor particles into low-melting Sn-P-F-O glass using phosphor-in-glass (PiG) approach. After being immersed in water for 96 h, the emission intensity of the SrLiAl3N4:Eu2+-PiG sample was maintained at 80% of its pristine intensity, indicating the moisture-resistance property of SrLiAl3N4:Eu2+ was significantly enhanced. Employing the narrow-band red-emitting SrLiAl3N4:Eu2+-PiG sample and a blue COB (chip-on-board), a plant growing LED device was fabricated. The emission spectrum of the device matches well with the absorption of Chlorophyl (a and b) in plants, indicating the as-prepared SrLiAl3N4:Eu2+-PiG are suitable to be applied in plant lighting field. We believe that this simple method reported in this communication can be easily expanded to other water-sensitive luminescence materials.

Photoluminescence properties and thermal stability of blue-emitting Ba5-xCl(PO4)3:xEu2+ (0.004≤x≤0.016) phosphors.

A series of blue-emitting Ba5-xCl(PO4)3:xEu2+ (0.004≤x≤0.016) phosphors were synthesized by conventional high-temperature solid state reaction. The structure and photoluminescence (PL) properties of the phosphors were investigated. The as-prepared phosphors exhibit broad excitation band ranging from 250 to 420nm, and strong asymmetric blue emission band peaking at 436nm. The optimum concentration of Eu2+ in the Ba5Cl(PO4)3:Eu2+ phosphor is x=0.01, and the concentration quenching mechanism is verified to be the combined actions of dipole-dipole interaction and radiation re-absorption mechanism. The thermal stability of Ba5Cl(PO4)3:Eu2+ was evaluated by temperature-dependent PL spectra. Compared with that of commercial BaMgAl10O17:Eu2+ (BAM) phosphor, the Ba5-xCl(PO4)3:xEu2+ phosphors exhibit similarly excellent thermal quenching property. In addition, the CIE chromaticity coordinates of Ba5-xCl(PO4)3:xEu2+ (0.004≤x≤0.016) were calculated to evaluate the color quality. All the results indicate that Ba5Cl(PO4)3:Eu2+ is a promising candidate phosphor for near-ultraviolet (n-UV) pumped LED.

A new porous magnetic chitosan modified by melamine for fast and efficient adsorption of Cu(II) ions.

A new porous magnetic chitosan modified by melamine (MA-CS/Fe3O4) was synthesized. The compositions and surface topographies were characterized by infrared (IR) spectroscopy, X-ray diffraction (XRD) analysis, thermogravimetric (TG) analysis and scanning electron microscope (SEM), respectively. The results of adsorption kinetics showed the adsorption behavior could be better described by the pseudo-second-order equation (R>0.999). The adsorption isotherm was well fitted by the Langmuir equation (R>0.999), and the values of separation factors were in the range of 0-1.0. The maximum adsorption capacity for Cu(II) was 2.58mmolg(-1) at the optimal experimental conditions, which were pH=5.5, t=25min, C0=5.0mmolL(-1). The rate-controlling step was supposed to be chemical adsorption rather than mass transport. The adsorbent still exhibited high adsorption capacity after five regeneration cycles. The adsorption mechanism was due to coordination between Cu(II) and N atoms.

Preparation of triethylene-tetramine grafted magnetic chitosan for adsorption of Pb(II) ion from aqueous solutions.

In this paper, a novel triethylene-tetramine grafted magnetic chitosan was synthesized. The chemical structure and the percentage content of each element of chitosan and its derivatives were characterized by elemental analysis, infrared spectroscopy, solid state (13)C NMR, X-ray diffraction analysis and thermogravimetric analysis, respectively. Their surface topography was observed by the transmission electron microscope. The results of adsorption kinetics and adsorption thermodynamics showed the adsorption mechanism could be better described by the pseudo-second-order equation (R>0.999). The adsorption isotherm was well fitted by the Langmuir equation (R>0.999), and 0

Optimized photoluminescence of SrB2O4:Eu3+ red-emitting phosphor by charge compensation.

A novel red-emitting phosphor, SrB(2)O(4):Eu(3+), was synthesized by high temperature solid-state reaction and its photoluminescence properties were studied. The emission spectrum consists of four major emission bands. The emission peaks are located at 593, 612, 650 and 703nm, corresponding to the (5)D(0)→(7)F(1), (5)D(0)→(7)F(2), (5)D(0)→(7)F(3) and (5)D(0)→(7)F(4) typical transitions of Eu(3+), respectively. The effects of Eu(3+) doping content and charge compensators (Li(+), Na(+), K(+)) on photoluminescence of SrB(2)O(4):Eu(3+) phosphor were studied. The results show that the emission intensity can be affected by above factors and Na(+) is the optimal charge compensator for SrB(2)O(4):Eu(3+). The photoluminescence of NaSrB(2)O(4):Eu(3+) was compared with that of Y(2)O(2)S:Eu(3+). It implies that SrB(2)O(4):Eu(3+) is a good candidate as a red-emitting phosphor pumped by near-ultraviolet (NUV) InGaN chip for fabricating white light-emitting diodes (WLEDs).

Preparation, characterization and photoluminescence properties of BaB2O4: Eu3+ red phosphor.

A new red emitting BaB2O4: Eu3+ phosphor was synthesized by solid-state reaction method. X-ray powder diffraction (XRD) analysis confirmed the monoclinic formation of BaB2O4. Field-emission scanning electron-microscopy (FE-SEM) observation indicated that the microstructure of the phosphor consisted of irregular grains with heavy agglomerate phenomena. Upon excitation with 394 nm light, the BaB2O4: Eu3+ phosphor shows bright red emissions with the highest photoluminescence (PL) intensity at 611 nm due to 5D0→7F2 transitions of Eu3+ ions. The CIE chromaticity coordinates are calculated from the emission spectrum to be x=0.64, y=0.35. The effects of the Eu3+ concentration on the PL were investigated. The results showed that the optimum concentration of Eu3+ in BaB2O4 host is 6 mol% and the dipole-dipole interaction plays the major role in the mechanism of concentration quenching of Eu3+ in BaB2O4: Eu3+ phosphor. The effect of charge compensation on the emission intensity was also studied. The charge compensations of Li+, Na+ and K+ anions all increased the luminescent intensity of BaB2O4: Eu3+. K+ anion gave the best improvement to enhance the intensity of the emission, indicating K+ is the optimal charge compensator. All properties show that this phosphor could serve as a potential candidate for application as a red phosphor for NUV chip LED.