Well-Performed Green Phosphor BaY4Si5O17:Ce3+,Tb3+ with High Quantum Efficiency and Thermal Stability.

For Tb3+-doped green phosphors, the energy transfer from Ce3+ to Tb3+ can largely enhance the absorption of excitation; however, obtaining phosphors that exhibit both high quantum efficiency and thermal stability continues to pose a significant challenge. Herein, we established a paradigm to achieve novel silicate BaY4Si5O17 (BYSO):Ce3+,Tb3+. The near-ultraviolet light efficiently excites the BYSO:Ce3+ material, causing it to emit light at a wavelength of 408 nm. The photoluminescence of BYSO:0.12Ce3+ exhibits a relatively small Stokes shift and a thermal stability of 89.8% of the 303 K emission intensity at 423 K (89.8%@423 K). The energy transfer (ET) from Ce3+ to Tb3+ ions can be readily constructed in BYSO:Ce3+,Tb3+ utilizing the overlap between the Ce3+ emission and the Tb3+ excitation. The ET efficiency from the Ce3+ to Tb3+ ions reached 83.8% at y = 1.2 and a maximum of 94.6%. Finally, the optimized phosphor BYSO:0.12Ce3+,1.2Tb3+ had an internal quantum efficiency of 94.4% and had excellent thermal stability (96.1%@423 K). Our work pointed out the avenue to novel green phosphors with high efficiency and thermal stability by choosing appropriate host and construct efficient ET.

Remote Control and Noninvasive Detection Enabled by a High-performance NIR pc-LED.

In an increasing manner, near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are considered to be exemplary light sources owing to their notable attributes of elevated output power, economical nature, and exceptional portability. NIR phosphors are critical components of NIR pc-LEDs. Herein, we report a novel blue light excitable NIR phosphor CaLu2ZrScAl3O12:Cr3+ (CLZSA:Cr3+) as a crucial and efficient broadband NIR emitter. The CLZSA:Cr3+ phosphor displays an intense NIR broadband emission peaking at 776 nm and with a full width at half-maximum (fwhm) of 140 nm. The designed material also exhibits superior resistance to thermal quenching, as the intensity of emission at 423 K remains at 80% of that at room temperature. The constructed NIR pc-LED device based on CLZSA:Cr3+ demonstrates a high total output power of 68.4 mW at a drive current of 100 mA, along with a high photoelectric conversion efficiency of 23.0%. Impressively, the high-power NIR pc-LEDs are utilized as light sources for remote control and non-invasive detection, resulting in the excellent performance and remarkable achievement.

Crystal Field Engineering Yields New 3D Layered Solid Solution Phosphors (Ca/Sr)4MgAl2Si3O14:Eu2+ for White-Light-Emitting Diode Full-Spectrum Lighting.

The cation-equivalent substitution strategy has the ability to manipulate the luminescence color of phosphors and enhance their overall luminescence performance. A series of novel yellow feldspar-type 3D layered phosphors (Ca1-ySry)4MgAl2Si3O14:xEu2+ were synthesized using a high-temperature solid-state reaction. The solid solution phosphors belong to a tetragonal crystal system with a space group of P4̅21m and cell parameters of a = b = 7.75407-7.91794 Å, c = 5.04299-5.22543 Å, and V = 303.166-327.602 Å3. Under near-ultraviolet (n-UV) excitation, the luminescence color of the phosphor undergoes modulation from yellow-green (530 nm) to blue (467 nm) as the Sr2+ ion substitution ratio increases. This modulation is attributed to the gradual decrease in crystal field splitting energy. Additionally, both the Stokes shift and the full width of the luminescence spectra decrease. Furthermore, there is an increase in the quantum yield (QY) from 45.50 to 60.73%. Finally, the fabricated white-light-emitting diode devices emitted warm white light and achieved high Ra (Ra = 94, 96.6, 92.7) and low correlated color temperature (CCT = 3486, 3430, 3788 K), indicating that the prepared solid solution phosphors can be used as candidate materials for WLED lighting.

Broadband Near-Infrared-Emitting Phosphors with Suppressed Concentration Quenching in a Two-Dimensional Structure.

For inorganic luminescent materials with activators, the energy yield is usually observed to decrease with an increase in activator concentration, which is known as the concentration quenching effect. To inhibit this phenomenon, a common strategy is to increase the distance between activators. Most previous reports have focused on the three-dimensional crystal lattice, and there have been few reports about two-dimensional layered structure. Herein, we synthesized a novel Cr3+-activated near-infrared (NIR) phosphor Li2Sr2Al(PO4)3 (LSAPO) with layered structure, and in such a two-dimensional structure, we proved experimentally that the concentration quenching was suppressed. Under 460 nm excitation, LSAPO:Cr3+ gave a broad NIR emission band (700-1200 nm) centered at 823 nm with a full width at half-maximum (fwhm) of 178 nm and a broad absorption band, indicating its potential application in NIR spectroscopy. Moreover, by codoping Cr3+ and Yb3+ ions, we further widened the emission bandwidth to ∼230 nm of fwhm, the internal quantum efficiency increased from 54% to 61%, and the thermal stability was improved. The fabricated NIR device with a LSAPO:Cr3+,Yb3+ phosphor coupled with blue chips can be applied in night-vision technologies and medical fields.

Double Perovskite Mn4+-Doped La2CaSnO6/La2MgSnO6 Phosphor for Near-Ultraviolet Light Excited W-LEDs and Plant Growth.

Non-rare earth doped oxide phosphors with far-red emission have become one of the hot spots of current research due to their low price and excellent physicochemical stability as the red component in white light-emitting diodes (W-LEDs) and plant growth. Herein, we report novel Mn4+-doped La2CaSnO6 and La2MgSnO6 phosphors by high-temperature solid-phase synthesis and analyzed their crystal structures by XRD and Rietveld refinement. Their excitation spectra consist of two distinct excitation bands with the dominant excitation range from 250 to 450 nm, indicating that they possess strong absorption of near-ultraviolet light. Their emission is located around 693 and 708 nm, respectively, and can be absorbed by the photosensitive pigments Pr and Pfr, proving their great potential for plant growth. Finally, the prepared samples were coated with 365 nm UV chips to fabricate far-red LEDs and W-LEDs with low correlation color temperature (CCT = 4958 K/5275 K) and high color rendering index (Ra = 96.4/96.6). Our results indicate that La2CaSnO6:Mn4+ and La2MgSnO6:Mn4+ red phosphors could be used as candidate materials for W-LED lighting and plant growth.

Synthesis, Characterization, and Catalytic Study of Amine-Bridged Bis(phenolato) Co(II) and Co(II/III)-M(I) Complexes (M = K or Na).

Co(II) complexes 1-3 bearing amine-bridged bis(phenolato) complexes have been synthesized through reactions of bis(phenols) with CoCl2 or Co(OAc)2. Oxidation of the Co(II) complex with air resulted in partial oxidation, generating mixed valence Co(II/III) complexes 4 and 5. In addition, due to the presence of alkali compounds (KOAc and NaOMe), 4 and 5 formed as Co-alkali metal heterometallic complexes, which are the first example of mixed valence Co(II/III)-M(I) (M = K or Na) complexes. Complexes 1-5 showed good activity in the cycloaddition of epoxides and CO2 under atmospheric pressure, generating cyclic carbonates in 40-99% yields. Co(II/III)-Na(I) complex 5 performed better in reactions of bulkier substrates, underlining the enhanced activity of mixed valence Co-alkali metal heterometallic complexes. On the contrary, complex 5 showed limited activity in copolymerization of epoxide and CO2.

UCNP-Bi2 Se3 Upconverting Nanohybrid for Upconversion Luminescence and CT Imaging and Photothermal Therapy.

Non-invasive theranostics that integrate the advantages of multimodality imaging and therapeutics have great potential in the field of biomedicine. Herein, a new nanohybrid based on Bi2 Se3 -conjugated upconversion nanoparticles (UCNPs) has been successfully developed through a simple in situ growth strategy. Under 808 nm near-infrared laser irradiation, the UCNPs can emit bright visible light, whereas the Bi2 Se3 nanomaterial exhibits efficient photothermal conversion capacity. Moreover, the as-synthesized UCNP-Bi2 Se3 nanohybrid exhibits efficient cell upconversion luminescence (UCL), reasonable CT imaging, and admirable cancer cell ablation capacity, further emphasizing the efficiency of this strategy for simultaneous UCL imaging and photothermal therapy. The designed theranostic strategy guided by dual-modal imaging endowed with real-time dynamic monitoring, remote controllability, and non-invasiveness makes the UCNP-Bi2 Se3 nanohybrid an ideal candidate for non-invasive multimodal imaging-guided photothermal therapy for the precise diagnosis and treatment of cancer.

ZnGa2-yAlyO4:Mn2+,Mn4+ Thermochromic Phosphors: Valence State Control and Optical Temperature Sensing.

Dual-emitting and thermochromic manganese ion single doped ZnGa2-yAlyO4 phosphors were prepared by solid-state reaction. The regulation of the valence state and the luminescent properties, especially the luminescent thermal stability of manganese ions in ZnGa2-yAlyO4, are discussed in detail. When excited by ultraviolet (UV) light, the emission spectra of ZnGa2O4:Mn2+,Mn4+ present an ultranarrow green emission band at 503 nm with a fwhm of 22 nm, which derives from the Mn2+ ions formed by the self-reduction of doped Mn4+, and a red emission band of the Mn4+ ions at 669 nm. In addition, a ZnGa2-yAlyO4:Mn2+,Mn4+ solid solution was designed and synthesized by Al3+ replacing Ga3+. The doping of Al3+ effectively inhibited the degree of Mn4+ self-reduction to Mn2+, thus realizing the regulation of valence state of manganese ions. Interestingly, the thermal stability of luminescence shows that the response of Mn2+ and Mn4+ to temperature is obviously different in ZnGa2-yAlyO4, implying the potential of the prepared phosphors as optical thermometers. Subsequently, three kinds of optical thermometers with superior color discrimination and high relative sensitivity (Sr) based on the fluorescence intensity ratio (FIR) technique were realized in 100-475 K. The Sr value of ZGO:0.005Mn/ZGA0.5O:0.005Mn/ZGAO:0.005Mn phosphors can be as high as 4.345%/4.001%/3.488% K-1 (at 350/325/400 K), reflecting the great potential of ZnGa2O4:Mn2+,Mn4+ for optical thermometry applications.

Engineered Anisotropic Fluids of Rare-Earth Nanomaterials.

The self-assembly of inorganic nanoparticles into well-ordered structures in the absence of solvents is generally hindered by van der Waals forces, leading to random aggregates between them. To address the problem, we functionalized rigid rare-earth (RE) nanoparticles with a layer of flexible polymers by electrostatic complexation. Consequently, an ordered and solvent-free liquid crystal (LC) state of RE nanoparticles was realized. The RE nanomaterials including nanospheres, nanorods, nanodiscs, microprisms, and nanowires all show a typical nematic LC phase with one-dimensional orientational order, while their microstructures strongly depend on the particles' shape and size. Interestingly, the solvent-free thermotropic LCs possess an extremely wide temperature range from -40 °C to 200 °C. The intrinsic ordering and fluidity endow anisotropic luminescence properties in the system of shearing-aligned RE LCs, offering potential applications in anisotropic optical micro-devices.

Phase-Tunable Synthesis of Monodisperse YPO4:Ln3+ (Ln = Ce, Eu, Tb) Micro/Nanocrystals via Topotactic Transformation Route with Multicolor Luminescence Properties.

A novel aqueous-based and phase-selected synthetic strategy toward YPO4:Ln3+ (Ln = Ce, Eu, Tb) micro/nanocrystals was developed by selecting specific precursors whose structure topotactically matches with the target ones. It was found that layered yttrium hydroxide (LYH) induced the formation of hexagonal-phased h-YPO4·0.8H2O with the crystalline relationship of [001]LYH//[0001]h-YPO4·0.8H2O, while the amorphous Y(OH)CO3 favored the formation of tetragonal-phased t-YPO4. We also systematically investigated the influence of Na2CO3/NaH2PO4 feeding ratio on the evolutions of morphology and size of the h-YPO4·0.8H2O sample, and we also obtained a novel mesoporous nanostructure for t-YPO4 single crystalline with closed octahedron shape for the first time. Besides, the multicolor and phase-dependent luminescence properties of the as-obtained h-YPO4·0.8H2O and t-YPO4 micro/nanocrystals were also investigated in detail. Our work may provide some new guidance in synthesis of nanocrystals with target phase structure by rational selection of precursor with topotactic structural matching.

Emission Enhancement and Color Tuning for GdVO4:Ln3+ (Ln = Dy, Eu) by Surface Modification at Single Wavelength Excitation.

The surface modification can realize systematically the emission enhancement of GdVO4:Ln3+ (Ln = Dy, Eu) microstructures and multicolor emission at single component. The structure, morphology, composition, and the surface ligands modification of as-prepared samples were studied in detail. It is found that the surface-modified ligands can act as sensitizer to improve the emission of the Eu3+ and Dy3+ ions via the energy transfer besides the VO43--Eu3+/Dy3+ process. More importantly, under a single wavelength excitation, the emission color can be effectively tuned by manipulating the doping ratio of the Eu3+ ions in the internal crystal lattice and the Tb3+ ions in the external surface ligands, simultaneously. And further, multicolor emissions are obtained under single wavelength excitation due to the high overlapping between the VO43- absorption and the π-π* electron transition of the ligands. These findings may open new avenues to design and develop new highly efficient luminescent materials.

Potential color tunable Sr3LaNa(PO4)3F:Eu2+/Tb3+/Mn2+ phosphor induced by Eu2+ → Tb3+ and Tb3+ → Mn2+ energy transfer for WLEDs.

Color tunable Sr3LaNa(PO4)3F:Eu2+,Tb3+ and Sr3LaNa(PO4)3F:Tb3+,Mn2+ phosphors were prepared by a high temperature solid state reaction. The crystal structure, luminescence properties, and energy transfer mechanism of the samples were investigated in detail. The Eu2+ doped phosphors can be efficiently excited in the range from 250 to 410 nm, which matches well with the commercial n-UV LED chips. Utilizing the energy transfer from Eu2+ to Tb3+ ions, tunable colors from blue to green were obtained under the irradiation of 405 nm. The mechanism of the Eu2+ → Tb3+ energy transfer was demonstrated to be a dipole-quadrupole interaction in terms of the experimental results and analysis of the photoluminescence spectra and decay curves of the phosphors. Moreover, the thermal stability and quantum efficiency of the Eu2+ and Tb3+ co-doped phosphors were studied. For the Sr3LaNa(PO4)3F:Tb3+,Mn2+ samples, tunable green-orange emissions were obtained by changing the relative ratio of Tb3+ and Mn2+ ions under 230 nm irradiation. The investigation results suggest that color tunable phosphors with potential for WLEDs were obtained utilizing the energy transfer process.

Novel tunable green-red-emitting oxynitride phosphors co-activated with Ce3+, Tb3+, and Eu3+: photoluminescence and energy transfer.

A series of novel Ce3+, Tb3+ and Eu3+ ion doped Y4SiAlO8N-based oxynitride phosphors were synthesized by the solid-state method and characterized by X-ray powder diffraction, scanning electron microscopy, photoluminescence, lifetimes and thermo-luminescence. The excitation of the Ce3+/Tb3+ co-doped and Ce3+/Tb3+/Eu3+ tri-doped phosphor with near-UV radiation results in strong linear Tb3+ green and Eu3+ red emission. The occurrence of Ce3+-Tb3+ and Ce3+-Tb3+-Eu3+ energy transfer processes is responsible for the bright green or red luminescence. The Tb3+ ion acting as an energy transfer bridge can alleviate MMCT quenching between the Ce3+-Eu3+ ion pairs. The lifetime measurements demonstrated that the energy-transfer mechanisms of Ce3+→ Tb3+ and Tb3+→ Eu3+ are dipole-quadrupole and quadrupole-quadrupole interactions, respectively. The temperature dependent luminescence measurements showed that as-prepared green/red phosphors have good thermal stability against temperature quenching. The obtained results indicate that these phosphors might serve as promising candidates for n-UV LEDs.

Broadband Yellowish-Green Emitting Ba4Gd3Na3(PO4)6F2:Eu(2+) Phosphor: Structure Refinement, Energy Transfer, and Thermal Stability.

A series of Ba4Gd3Na3(PO4)6F2:Eu(2+) phosphors with a broad emitting band have been synthesized by a traditional solid state reaction. The crystal structural and photoluminescence properties of Ba4Gd3Na3(PO4)6F2:Eu(2+) are investigated. The different crystallographic sites of Eu(2+) in Ba4Gd3Na3(PO4)6F2:Eu(2+) phosphors have been verified by means of their photoluminescence (PL) properties and decay times. Energy transfer between Eu(2+) ions, analyzed by excitation, emission, and PL decay behavior, has been indicated to be a dipole-dipole mechanism. Moreover, the luminescence quantum yield as well as the thermal stability of the Ba4Gd3Na3(PO4)6F2:Eu(2+) phosphor have been investigated systematically. The as-prepared Ba4Gd3Na3(PO4)6F2:Eu(2+) phosphor can act as a promising candidate for n-UV convertible white LEDs.

Topotactic Transformation Route to Monodisperse ß-NaYF4:Ln(3+) Microcrystals with Luminescence Properties.

A novel nonorganic wet route for direct synthesis of uniform hexagonal ß-NaYF4:Ln(3+) (Ln = Eu, Tb, Ce/Tb, Yb/Er, and Yb/Tm) microcrystals with various morphologies has been developed wherein the intermediate routine cubic-hexagonal (α → ß) phase transfer process was avoided. The morphology can be effectively tuned into hexagonal disc, prism, and novel hierarchical architectures by systematically fine manipulating the Na2CO3/F(-) feeding ratio. It has been found that the routine α → ß phase transfer for NaYF4 was not detected during the growth, while NaY(CO3)F2 emerged in the initial reaction stage and fast transformed into ß-NaYF4 via a novel topotactic transformation behavior. Detailed structural analysis showed that ß-NaYF4 preferred the [001] epitaxial growth direction of NaY(CO3)F2 due to the structural matching of [001]NaY(CO3)F2//[0001]ß-NaYF4. Besides, the potential application of the as-prepared products as phosphors is emphasized by demonstrating multicolor emissions including downconversion, upconversion, and energy transfer (Ce-Tb) process by lanthanides doping.

Synthesis, structure, and photoluminescence properties of novel KBaSc2 (PO4 )3 :Ce(3+) /Eu(2+) /Tb(3+) phosphors for white-light-emitting diodes.

A series of novel KBaSc2 (PO4 )3 :Ce(3+) /Eu(2+) /Tb(3+) phosphors are prepared using a solid-state reaction. X-ray diffraction analysis and Rietveld structure refinement are used to check the phase purity and crystal structure of the prepared samples. Ce(3+) - and Eu(2+) -doped phosphors both have broad excitation and emission bands, owing to the spin- and orbital-allowed electron transition between the 4f and 5d energy levels. By co-doping the KBaSc2 (PO4 )3 :Eu(2+) and KBaSc2 (PO4 )3 :Ce(3+) phosphors with Tb(3+) ions, tunable colors from blue to green can be obtained. The critical distance between the Eu(2+) and Tb(3+) ions is calculated by a concentration quenching method and the energy-transfer mechanism for Eu(2+) →Tb(3+) is studied by utilizing the Inokuti-Hirayama model. In addition, the quantum efficiencies of the prepared samples are measured. The results indicate that KBaSc2 (PO4 )3 :Eu(2+) ,Tb(3+) and KBaSc2 (PO4 )3 :Ce(3+) ,Tb(3+) phosphors might have potential applications in UV-excited white-light-emitting diodes.

Luminescence properties of Ca2 Ga2 SiO7 :RE phosphors for UV white-light-emitting diodes.

A series of Eu(2+) -, Ce(3+) -, and Tb(3+) -doped Ca2 Ga2 SiO7 phosphors is synthesized by using a high-temperature solid-state reaction. The powder X-ray diffraction and structure refinement data indicate that our prepared phosphors are single phased and the phosphor crystalizes in a tetrahedral system with the ${P\bar 42m}$ (113) space group. The Eu(2+) - and Ce(3+) -doped phosphors both have broad excitation bands, which match well with the UV light-emitting diodes chips. Under irradiation of λ=350 nm, Ca2 Ga2 SiO7 :Eu(2+) and Ca2 Ga2 SiO7 :Ce(3+) , Li(+) have green and blue emissions, respectively. Luminescence of Ca2 Ga2 SiO7 :Tb(3+) , Li(+) phosphor varies with the different Tb(3+) contents. The thermal stability and energy-migration mechanism of Ca2 Ga2 SiO7 :Eu(2+) are also studied. The investigation results indicate that the prepared Ca2 Ga2 SiO7 :Eu(2+) and Ca2 Ga2 SiO7 :Ce(3+) , Li(+) samples show potential as green and blue phosphors, respectively, for UV-excited white-light-emitting diodes.

Enhancing photoluminescence performance of SrSi2O2N2:Eu(2+) phosphors by Re (Re = La, Gd, Y, Dy, Lu, Sc) substitution and its thermal quenching behavior investigation.

Eu(2+)-doped SrSi2O2N2 has recently been identified as a viable green phosphor that in conjunction with a blue-emitting diode can be used in solid-state white-lighting sources. In this study, we attempt to improve the photoluminescence and thermal quenching behavior by codoping Re(3+) (Re = La, Gd, Y, Dy, Lu, Sc) and Li(+) instead of Sr(2+). Trivalent cation substitution at the Sr(2+) site enhances the photoluminescence intensities and also achieves better thermal stability at high temperature. The lifetime decay properties in the related substituted phosphors are investigated. Furthermore, under the 460 nm blue light irradiation, this green phosphor exhibits excellent luminescence properties with absorption and internal/external efficiencies. High-color-rendition warm-white LEDs using the phosphor have the color temperature and color rendition of 4732 K and 91.2, respectively, validating its suitability for use in solid-state white lighting.

A novel efficient Mn4+ activated Ca14Al10Zn6O35 phosphor: application in red-emitting and white LEDs.

A new, highly efficient deep red-emitting phosphor Ca14Al10Zn6O35:Mn(4+) was developed as a component of solid-state white light-emitting diodes (LEDs). The structural and optical characterization of the phosphor is described. The phosphor exhibits strong emission in the range of 650-700 nm when excited by 460 nm excitation, with a quantum efficiency approaching 50%. Concentration dependence of Mn(4+) luminescence in Ca14Al10Zn6O35:Mn(4+) is investigated. Attempts to understand the thermal stability on the basis of the thermal quenching characteristics of Ca14Al10Zn6O35:Mn(4+) is presented. The results suggest that phosphors deriving from Ca14Al10Zn6O35:Mn(4+) have potential application for white LEDs. In addition, influence of cation substitution on the luminescence intensity of these phosphors is elucidated.

Ba(1.3)Ca(0.7)SiO4:Eu(2+),Mn(2+): a promising single-phase, color-tunable phosphor for near-ultraviolet white-light-emitting diodes.

In this paper, Eu(2+)-doped and Eu(2+)/Mn(2+)-codoped Ba1.3Ca0.7SiO4 phosphors were synthesized by means of a conventional solid-state reaction process. The single-phase purity was checked by means of X-ray diffraction and the Rietveld method. Under excitation at 390 nm, the emission spectra of the Eu(2+)-doped phosphors exhibit a broad-band emission centered at 500 nm caused by the electric dipole allowed transition of the Eu(2+) ions. The emission spectra of codoped phosphors show one more broad emission centered at 600 nm attributable to the transitions from the (4)T1((4)G) → (6)A1((6)S) of Mn(2+) ions. The luminescent color of the codoped phosphors can be easily adjusted from blue to red with variation of the Mn(2+) content. The energy transfer mechanism from the Eu(2+) to Mn(2+) ions in Ba1.3Ca0.7SiO4 phosphors has been confirmed to be the resonant type via dipole-quadrupole interaction, and the critical distance has been calculated quantitatively. All these results demonstrate that the Eu(2+)/Mn(2+)-codoped Ba1.3Ca0.7SiO4 phosphors can be a promising single-phase, color-tunable phosphor for near-UV white-light-emitting diodes after a further optimization process. Additionally, a great red shift from 593 to 620 nm has been observed following the increase of Mn(2+) content, and the phenomenon has been discussed in relation to the changes in the crystal field surrounding the Mn(2+) ions and the exchange interactions caused by the formation of Mn(2+) pairs.