Single-nodal linking for Zn2 +-Nd3 +-containing metallopolymer with efficient near-infrared (NIR) luminescence

Through the single-nodal copolymerization of MMA (methyl methacrylate) and a vinyl-containing complex monomer [Zn(L)(4-vinyl-Py)Nd(NO₃)₃] (2; H₂L = N,N′-bis(3-methoxy-salicylidene)ethylene-1,2-diamine; 4-vinyl-Py = 4-vinyl-pyridine) with the both ¹π-π* and ³π-π* sensitizing approach to Nd^3 + ion, the Zn^2 +-Nd^3 +-containing metallopolymer Poly(MMA-co-2) exhibits good physical properties including an attractive Nd^3 +-centered NIR sensitization efficiency (Φ^L_Nd = 1.22% and η = Φ^L_Nd/Φ^Nd_Nd = 82%).     

Site construction of Eu2+ and sensitized luminescence of Eu3+ in LaF3:Eu nanophosphor

LaF₃:Eu nanophosphors were prepared by a traditional hydrothermal method with citric acid as a reducing agent. X-ray diffraction, scanning electronic microscopy, and luminescence spectroscopy were used to study the nanophosphors. The formation of three different luminescence centers of Eu²⁺ and two different luminescence centers of Eu³⁺ is attributed to the existence of abundant surface defects in this nanophosphor. Eu³⁺ is effectively excited by energy transfer from Eu²⁺ to Eu³⁺. The excitation wavelength of Eu³⁺ covers a broad spectral range from 250 to 480 nm. The nanophosphor shows a tunable luminescence color varying from blue to white and then to red, which is explained from three aspects of Eu concentration, energy transfer, and concentration quenching. Utilizing the surface defect of nanoparticles to control the reduction of Eu³⁺ is considered a promising strategy for exploring Eu²⁺ and Eu³⁺ codoped phosphor suitable for the lighting and display application.     

SrLaNaTeO6:Eu3+ red-emitting phosphors with high luminescence efficiency and high thermal stability for high CRI white LEDs

A novel single-phase trivalent europium activated red-emitting SrLaNaTeO₆ phosphor was first synthesized in a process of traditional high-temperature solid-state. The phase purity, morphology, and spectroscopy of the prepared phosphor were analyzed. Under 395 nm excitation, the photoluminescence (PL) spectra of the SrLaNaTeO₆:Eu³⁺ products mainly contained five dominant sharp peaks. The intense red emission peak at 615 nm was the typical ⁵D₀→⁷F₂ electric dipole transition of Eu³⁺. The optimum product of high quenching concentration was the SrLaNaTeO₆:0.90Eu³⁺, which reached a high internal quantum efficiency (IQE) of 90.6%. The SrLaNaTeO₆:0.90Eu³⁺ was estimated to have R_c of 6.57 Å and possessed high color purity of 100.0%. The phosphors exhibited excellent thermal stability and high activation energy (E_a = 0.29 eV). The prepared white light-emitting diode (WLED) had a high color rendering index (CRI) R_a of 92 and a low correlated color temperature (CCT) of 5008 K. In conclusion, the phosphors have potential as red components for WLEDs.     

Uniform colloidal spheres for RE3BO6 (RE = Eu-Yb,Y) and excitation-dependent luminescence of Y3BO6:Eu3+ red phosphor

Phosphor particles of spherical shape and uniform size are desired for high-definition displays to improve the resolution and the overall luminescent performance. However, the synthesis of RE₃BO₆ spherical particles is a considerable challenge in materials science. Here, uniform spheres of RE₃BO₆ (RE = Eu–Yb, Y) have been converted from their colloidal precursor spheres synthesized via homogeneous precipitation. The amorphous precursor spheres are solid particles with decreased boron going from the surfaces to the cores. Smaller particles were observed at decreased ionic radius from Eu³⁺ to Ho³⁺ (including Y³⁺), but particles with nearly unvaried sizes were observed by further decreasing the ionic radius from Ho³⁺ to Yb³⁺. They crystallized in monoclinic RE₃BO₆ at 900°C, with maintaining the spherical shape of precursors. However, the crystal growth and the densification toward the particle surfaces resulted in the formation of hollow spheres for smaller particles and core-shell structured spheres for larger particles. The parameters, a, b, and c, increase nearly monotonically with increasing the radius of rare earth ions. The uniform spheres of Y₃BO₆:Eu³⁺ exhibited a typical red emission at ~613 nm (⁵D₀ → ⁷F₂ electric dipole transition of Eu³⁺), with an intensity ratio I(⁵D₀ → ⁷F₂)/I(⁵D₀ → ⁷F₁) of ~3.5. The luminescence behavior of Y₃BO₆:Eu³⁺ phosphor is dependent on the excitation wavelength, which is closely related to the Eu³⁺ ions at different coordination sites. Driven by a 460-nm blue-LED chip, the Y₃BO₆:Eu³⁺ spheres exhibited a red emission with the CIE coordinates of (~0.65, ~0.35), indicating that they are an excellent red-emitting phosphor candidate for application in white-LEDs.     

Pure white-light and color-tuning of PMMA-supported hybrid materials doped with (TTA)3-Zn2 +-Eu3 + and (BA)3-Zn2 +-Tb3 + complexes

Based on the doping of red-light-emitting 2 ([Zn(L)(4-vinyl-Py)Eu(TTA)₃]; H₂L = N,N′-bis(salicylidene)cyclohexane-1,2-diamine, 4-vinyl-Py = 4-vinyl-pyridine, HTTA = 2-thenoyltrifluoroacetonate) and cyan-light-emitting 4 ([Zn(L)(4-vinyl-Py)Tb(BA)₃]; HBA = 1-phenyl-1,3-butanedione) in PMMA, hybrid materials of 2@4@PMMA with improved physical properties including color-tunable for white-light (CIE coordinate 0.373, 0.319) were obtained.     

Lanthanide coordination polymers for multi-color luminescence and sensing of Fe3 +

Luminescent lanthanide coordination polymers [H₂NMe₂]₃[Ln(DPA)₃] (Ln = Eu, Tb, Sm, Dy; [H₂NMe₂]⁺ = dimethyl amino cation; H₂DPA = 2,6-dipicolinic acid) are synthesized, whose multi-color can be tuned and even white color luminescence can be integrated. Besides, the fluorescent sensing property of the [H₂NMe₂]₃[Tb(DPA)₃] system is checked, which shows selective fluorescent quenching effect for Fe^3 +.     

Luminescent Eu3+-doped transparent alumina ceramics with high hardness

The Eu³⁺-doped transparent aluminas were prepared by wet shaping technique followed by pressure-less sintering and hot isostatic pressing. The effect of dopant amount on microstructure, real in-line transmission (RIT), photoluminescence (PL) properties, hardness and fracture behaviour was studied. The RIT decreased with increasing amount of the dopant. The PL emission spectra of Al₂O₃:Eu³⁺ ceramics exhibited predominant red light emission with the highest intensity (under 394 nm excitation) for material containing 0.125 at.% of Eu³⁺ and colour coordinates (0.645, 0.355) comparable with commercial red phosphors. The doping resulted in hardness increase from 26.1 GPa for undoped alumina to 27.6 GPa for Eu-doped sample. The study of fracture surfaces showed predominantly intergranular crack propagation micro-mechanism.     

Effective sensitization of Eu3+ ions on Eu3+/Nd3+ co-doped multicomponent borosilicate glasses for visible and NIR luminescence applications

Eu³⁺/Nd³⁺ co-doped multicomponent borosilicate glasses (ND1E: 10BaO +10ZnF₂+10K₂O +20SiO₂+(49-x) B₂O₃+1Nd₂O₃+xEu₂O₃) were prepared by conventional melting and rapid quench technique to evaluate the effect of Eu³⁺ ions in the Nd³⁺ doped glasses. Thermal stability, structural and spectroscopic characteristics of the ND1E glasses were investigated by using DSC, XRD, FTIR, Optical absorption, excitation and emission measurements. The Judd – Ofelt (JO) analysis is implemented to the absorption spectrum of the prepared glassy matrix in order to identify their potential applicability in lasing devices. Enhancement of ⁷F₀ → ⁵L₆ band (394 nm) with the increasing concentration of Eu³⁺ ion in the Nd³⁺ excitation spectra (λ_emi = 1060 nm) reveals the possibility of obtaining the characteristic fluorescence spectra of Nd³⁺ ion with the typical excitation wavelengths (Nd³⁺ = 584 nm and Eu³⁺ = 394 nm) of both rare earth ions and it is further verified from the emission spectrum. This interesting luminescence effect of showing excellent visible and NIR emission under 394 nm excitation mainly attributes the energy transfer mechanism between the RE³⁺ ions and the reason underlying this effect is discussed in detail with the help of partial energy level diagram. Energy transfer efficiency between the Eu³⁺ and Nd³⁺ ions were evaluated by using the radiative lifetimes of the prepared glasses. Also, a comparison of radiative properties and lasing characteristics of Eu³⁺/Nd³⁺ co-doped glasses with other Nd³⁺ glasses are reported. The emission intensities were characterized using CIE chromaticity diagram and the observed CIE coordinates shows a shift towards reddish – orange region with the increase in Eu³⁺ concentration. The quantum efficiency of the prepared glasses was determined experimentally. The obtained results suggest that the ND1E glassy system can be considered as a potential candidate for visible and NIR luminescence applications.     

Fabrication and characterizations of Eu2+-Dy3+ co-doped SrAl2O4 ceramics with persistent luminescence

(Sr_0.97Eu_0.01Dy_0.02)Al₂O₄ persistent luminescence (PersL) ceramics were fabricated by solid-state reactive sintering in vacuum combined with hot isostatic pressing (HIP) using H₃BO₃ as a sintering additive. The phase composition, microstructure, luminescence properties, trap state, and PersL performance of HIP post-treated (Sr_0.97Eu_0.01Dy_0.02)Al₂O₄ PersL ceramics were discussed. For the (Sr_0.97Eu_0.01Dy_0.02)Al₂O₄ PersL ceramics after HIP post-treatment, the initial luminescence intensity of the ceramics reached over 6400 mcd/m² with simulated daylight irradiation of 1000 lx for 5 min, and the persistent emission decay time > 17 h. This is much better than the SrAl₂O₄:Eu²⁺,Dy³⁺ PersL powders and the other luminescent ceramics. In addition, this method is a solid-state reactive sintering method for synthesizing ceramics, which has the advantages of low cost and simple operation, and is suitable for large-scale, high-volume industrial production.     

Enhanced luminescence properties of Eu3+ in La2MoO6 by nonsensitization of Bi3+

It was unusual for Bi³⁺ ions to enhance the emission intensity of phosphors via nonsensitization. Here, La₂MoO₆:Eu³⁺, Bi³⁺ phosphors were successfully synthesized by a high temperature solid-state reaction method in air atmosphere. As the increase of doping concentration of Bi³⁺, the emission spectra of La₂MoO₆:Eu³⁺, Bi³⁺ phosphors had obvious shifts, splits and the enhancement of intensities, which indicated that the characteristics of the phosphors were modified. To analyze these phenomena, the crystal structure refinements, spectral characteristic analyze and Judd-Ofelt theoretical calculation were mainly performed. Bi³⁺ ions played the role of the nonsensitizer and affected the distortion of the crystal, the sites of Eu³⁺ ions, the field splitting energy and the internal quantum yield. Moreover the nephelauxetic effects of Bi³⁺ ions and the ET process caused synergistically the life times of La₂MoO₆:Eu³⁺, Bi³⁺ phosphors to increase and then gradually decrease. The CIE coordinates of phosphors changed within a small range. This study might be instrumental in promoting the further application of Bi³⁺ ions in rare earth luminescent materials.     

Synthesis and luminescence properties of color-tunable Dy3+/Eu3+: CeAlON phosphors

Color-tunable Dy³⁺/Eu³⁺ co-doped in Ce₂AlO₃N phosphors were synthesized via a simple conventional solid state reaction. The as-prepared samples were characterized by XRD, TEM and photoluminescence spectra. Results show that the concentrations of Eu³⁺ ions can affect the blue and yellow emission intensities of Dy³⁺, and tunable emission color can be obtained by adjusting the doping concentrations of Eu³⁺. Based on the energy levers of Eu³⁺and Dy³⁺, the mechanism of tunable color has been presented in detail. The thermal stability of Dy³⁺/Eu³⁺: Ce₂AlO₃N has also been discussed.     

A novel scheelite-type LiCaGd(WO4)3:Eu3+ red phosphors with prominent thermal stability and high quantum efficiency

A series of LiCaGd(WO4)3 : xEu³⁺ (0 ≤ x ≤ 1.0) red phosphors with tetragonal scheelite structure were synthesized via the conventional solid-state reaction. Their crystal structure, photoluminescence excitation (PLE), and photoluminescence (PL) spectra, thermal stability and quantum efficiency were investigated. The phosphors exhibit a typical red light upon 395 nm near ultraviolet excitation, and the strongest emission peak at 617 nm is dominated by the ⁵D₀→⁷F₂ transition of Eu³⁺ ions. The PL intensity of the phosphors gradually increases with the increase of Eu³⁺ doping concentration, and the concentration quenching phenomenon is hardly observed. The quantum efficiency and the color purity of the phosphor reach maximum values of about 94.2 and 96.6% at x = 1.0, respectively. More importantly, LiCaGd(WO₄)₃:xEu³⁺ phosphors have prominent thermal stability. The temperature-dependent PL intensity of the phosphors at 423 K is only reduced to 89.1% of the PL intensity at 303 K, which is superior to that of commercial red phosphors Y₂O₃:Eu³⁺. Finally, LiCaGd(WO₄)₃:Eu³⁺ phosphor is packaged with near ultraviolet InGaN chips to fabricate white light emitting diodes, which has a low color temperature (CCT = 4622 K) and a high color rendering index (CRI= 89.6).     

Synthesis,structure and luminescence properties of a novel red fluorescent material Ba2MgB2O6:Eu3+

The crystal structure of Ba_2-xMgB₂O₆:xEu³⁺ phosphors, synthesized using a solid-state reaction, have been confirmed by X-ray diffraction analysis. This study focuses on the site occupancy preference of Eu³⁺ ions within the matrix, which was determined using bond energy theory, fluorescent spectra, and a consideration of energy transport and decay curves. The impact of Eu³⁺ ion concentration on luminescence has been assessed, and an optimal concentration (x = 0.22) identified. The critical distance, R_c was 9.6 Å, with a calculated θ value of 19.67, indicating that quadrupole-quadrupole interaction plays a critical role in the quenching Ba_2-xMgB₂O₆:xEu³⁺ phosphors. The Ba_2-xMgB₂O₆:xEu³⁺ phosphors exhibited a color purity of 99.26%, and a quantum efficiency of 49.68%. The activation energy Ea was determined to equal 0.2987 eV. The results have established Ba_1.78MgB₂O₆:0.22Eu³⁺ as a red fluorescent powder with high quantum efficiency and a millisecond fluorescence lifetime.     

One-step synthesis of Sc2W3O12:Eu3+ phosphors with tunable luminescence for WLED

Sc₂W₃O₁₂ is an important host matrix for rare-earth doped luminescence. However, the conventional method to prepare the material is solid-state reaction, which results into coarse and irregular morphologies. In this work, Eu³⁺ doped Sc₂W₃O₁₂ phosphors with high crystallinity and pure phase were successfully synthesized via one-step hydrothermal method. It was found that the crystalline phase changed from Sc₂W₃O₁₂ phase to Na₄Sc₂(WO₄)₅ phase when the molar ratio between Sc(NO₃)₃ and Na₂WO₄ decreased. The temperature-dependent X-ray diffraction analysis was performed to prove the negative thermal expansion property of Sc₂W₃O₁₂. A systematic study on the effect of reaction time, temperature and Eu³⁺ doping concentration was explored. It was also found that the as-prepared samples displayed tunable emission colors, ranging from blueish white to orange red. Particularly, the white light emission with the chromaticity coordinate of (0.3395, 0.3289) can be realized in Sc₂W₃O₁₂: 5% Eu³⁺. What's more, the photoluminescence properties of the samples were investigated under different ambient temperatures between 97 and 280?K. The result clearly showed energy transfer between Eu³⁺ and WO₄^2?. The above results suggested that Sc₂W₃O₁₂:Eu³⁺ can be excellent candidate for solid-state lasing, panel display and WLEDs.     

A novel strategy to achieve NaGdF4:Eu3+ nanofibers with color‐tailorable luminescence and paramagnetic performance

Luminescent‐magnetic bifunctional NaGdF₄:Eu³⁺ nanofibers were fabricated through the bond of electrospinning followed by calcination with fluorination technology for the first time. The structure, morphologies, luminescence, and magnetism of nanofibers have been characterized using various techniques. X‐ray diffraction measurement indicates that NaGdF₄:Eu³⁺ nanofibers are hexagonal phase. Scanning electron microscope measurement shows that the mean diameters of electrospinning‐made polyvinyl pyrrolidone/[NaNO₃+Gd(NO₃)₃+Eu(NO₃)₃] composite nanofibers and NaGdF₄:Eu³⁺ nanofibers are, respectively, 428±4 and 231±4 nm under the confidence level of 95%. Under 274‐nm ultraviolet light excitation, NaGdF₄:Eu³⁺ nanofibers exhibit characteristic ⁵D_3,2,1,0→⁷F_J emissions of Eu³⁺ and the tendency of color tones of samples varies from blue, cold white, warm white to red via varying Eu³⁺ content. In addition, samples exhibit paramagnetic features and the magnetic properties of NaGdF₄:Eu³⁺ nanofibers are tailorable by modulating the doping concentration of Eu³⁺. More importantly, the color‐tailorable luminescence and paramagnetic properties are simultaneously realized in single‐phase NaGdF₄:Eu³⁺ nanofibers, which ideally suit to apply in many fields such as lighting and color displays, bioimaging, and magnetic resonance imaging. This design conception and construction strategy may provide some new guidance for synthesizing other rare‐earth fluorides nanomaterials of multifarious morphologies.     

Toward tunable and bright deep‐red persistent luminescence of Cr3+ in garnets

Garnet structure (A₃B₂C₃O₁₂) with three different cation sites is a very flexible host material widely used for w‐LEDs, solid‐state lasers, scintillators, and so on. In this work, we have successfully developed six different Cr³⁺‐doped garnets: Y₃Ga_4.99Cr_0.01O₁₂ (YGG:Cr), Gd₃Ga_4.99Cr_0.01O₁₂ (GGG:Cr), Lu₃Ga_4.99Cr_0.01O₁₂ (LuGG:Cr), Y₃Sc_1.99Cr_0.01Ga₃O₁₂ (YSGG:Cr), Gd₃Sc_1.99Cr_0.01Ga₃O₁₂ (GSGG:Cr), and Lu₃Sc_1.99Cr_0.01Ga₃O₁₂ (LuSGG:Cr), which exhibit persistent luminescence (PersL) due to Cr³⁺ emission matching well with both the response curve of the Si detector and the wavelength region of the first biological window (NIR‐I, 650‐950 nm). The main emission band of Cr³⁺ in these garnets can be easily tunable from the sharp R‐line emission due to the ²E (²G)→⁴A₂ (⁴F) transition in the strong crystal field to the broad band emission due to the ⁴T₂ (⁴F)→⁴A₂ (⁴F) transition in the weak one when Lu³⁺ in the A site and Ga³⁺ in the B site are, respectively, replaced by larger cations, Y³⁺/Gd³⁺ and Sc³⁺. Furthermore, based on the knowledge of 4f energy levels of 15 lanthanide ions in the host‐referred binding energy (HRBE) diagram, we took the GSGG host as a typical example to discuss the feasibility of four trivalent lanthanides (Sm³⁺, Eu³⁺, Tm³⁺, Yb³⁺) as potential sensitizers for enhancing Cr³⁺ PersL.     

Eu3+ luminescence in novel garnet-type Li5La3Nb2O12 ceramics

A novel Li₅La₃Nb₂O₁₂:Eu³⁺ phosphor was synthesized by the solid-state reaction at high temperature. The phase purity of products was checked by XRD. The emission spectrum is independent of the excitation wavelength and the ⁵D₀–⁷F₂ transition is the dominant one. In the excitation spectrum, there are some sharp peaks originating from the f–f transitions of Eu³⁺ and a broad band peaking at about 280 nm. The concentration dependence of emission intensity and decay curves of ⁵D₀–⁷F₂ transition were investigated. The temperature dependence of emission intensity and decay curves were also investigated in detail.     

Controllable synthesis of bifunctional material Ca2Ti2O6:Eu3+ and its comparative study on luminescence and photocatalytic properties with CaTiO3:Eu3+

Pure pyrochlore Ca₂Ti₂O₆, perovskite CaTiO₃, and their mixed crystalline phases with different proportions were controllably synthesized via a solvothermal method, followed by a subsequent calcination process. RIR (reference intensity ratio) data of Ca₂Ti₂O₆ were first obtained by X-ray diffraction (XRD), which can be used to quantitatively analyze the phase composition. When Eu³⁺ is doped into these calcium titanium oxides, they can be used as luminescent and photocatalytic materials. The structure, luminescence, and photocatalytic properties of pure pyrochlore Ca₂Ti₂O₆:Eu³⁺ and perovskite CaTiO₃:Eu³⁺ were comparatively studied in detail. The relative intensities of the excitation peaks and the emission peaks in Ca₂Ti₂O₆:Eu³⁺ and CaTiO₃:Eu³⁺ are different, which is attributed to the different symmetries of Eu³⁺ inhabiting the two kinds of lattices. In addition, although the luminescence intensity of CaTiO₃:3%Eu³⁺ is higher than that of Ca₂Ti₂O₆:3%Eu³⁺ under excitation at 394 nm, the luminescence intensity of Ca₂Ti₂O₆:3%Eu³⁺ is superior to that of CaTiO₃:3%Eu³⁺ under excitation at 464 nm and 533 nm. Photocatalytic experiments show that Ca₂Ti₂O₆:3%Eu³⁺ has better photocatalytic performance than CaTiO₃:3%Eu³⁺, which is mainly due to its smaller crystallite size, higher specific surface area and pyrochlore structure. In addition, biphase (Ca₂Ti₂O₆–CaTiO₃):3%Eu³⁺ has the best photocatalytic activity compared with the single phase Ca₂Ti₂O₆:3%Eu³⁺ and CaTiO₃:3%Eu³⁺, owing to the presence of heterojunctions that significantly reduced the band gap. It is anticipated that the discovery of this bifunctional Ca₂Ti₂O₆:Eu³⁺ would expand the application of rare earth-doped calcium titanium oxide materials.     

Structural and luminescence properties of silica powders and transparent glass‐ceramics containing LaF3:Eu3+ nanocrystals

In this work, silica powders and transparent glass‐ceramic materials containing LaF₃:Eu³⁺ nanocrystals were synthesized using the low‐temperature sol‐gel technique. Prepared samples were characterized by TG/DSC analysis as well as X‐ray diffraction and IR spectroscopy. The transformation from liquid sols toward bulk powders and xerogels was also examined and analyzed. The optical behavior of prepared Eu³⁺‐doped sol‐gel samples were evaluated based on photoluminescence excitation (PLE: λ_em = 611 nm) and emission (PL: λ_exc = 393 nm, λ_exc = 397 nm) spectra as well as luminescence decay analysis. The series of luminescence lines located within reddish‐orange spectral scope were registered and identified as the intra‐configurational 4f⁶‐4f⁶ transitions originated from Eu³⁺ optically active ions (⁵D₀ → ⁷F_J, J = 0‐4). Moreover, the R/O‐ratio was also calculated to estimate the symmetry in local framework around Eu³⁺ ions. The luminescence spectra and double‐exponential character of decay curves recorded for fabricated nanocrystalline sol‐gel samples (τ₁(⁵D₀) = 2.07 ms, τ₂(⁵D₀) = 8.07 ms and τ₁(⁵D₀) = 0.79 ms, τ₂(⁵D₀) = 9.76 ms for powders and glass‐ceramics, respectively) indicated the successful migration of optically active Eu³⁺ ions from amorphous silica framework to low phonon energy LaF₃ nanocrystal phase.