Color tunable emission in Ce3+ and Tb3+ co-doped Ba2Ln(BO3)2Cl (Ln=Gd and Y) phosphors for white light-emitting diodes

Recent progress of effect of crystal structure on luminescence properties of Ce3+–Eu2+ Co-doped phosphors

Currently, the mechanism of Ce³⁺–Eu²⁺ ET is frequently used to obtain color adjustable or white phosphors. Correspondingly, the ET efficiency from Ce³⁺ to Eu²⁺ becomes an important indication of the luminescent properties of phosphors. However, the ET efficiency calculated using the formula does not always match the emission spectra; the transmission efficiency of Ce³⁺ is high, but the emission efficiency of Eu²⁺ is low, depending on our investigation results. In addition to this problem, here we mainly review, on the basis of substantial examples, how to boost the actual ET efficiency of Ce³⁺-to-Eu²⁺ and thus to improve the luminescent properties of phosphors through the rational design of layered crystal structure and the way of selective occupation of activator ions. Moreover, the possible physical mechanisms are proposed.

Effect of crystal structure on luminescence properties of Ce³⁺–Eu²⁺ co-doped phosphors.

The next generation vanadium flow batteries with high power density - a perspective

Vanadium flow batteries (VFBs) have received increasing attention due to their attractive features for large-scale energy storage applications. However, the relatively high cost and severe polarization of VFB energy storage systems at high current densities restrict their utilization in practical industrial applications. Optimization of the performance of key VFB materials, including electrodes, electrolytes and membranes, can realize simultaneous minimization of polarization and capacity decay. The power density and energy density of VFBs are thus simultaneously enhanced. Moreover, relevant theoretical mechanisms and foundations based on virtual investigations of VFB models and simulations can guide these optimizations. The improved power density and energy density can reduce the cost of VFB energy storage systems, accelerating their successful industrialization. In this perspective, modification methods to optimize the performance of key VFB materials and investigations of models and simulations of VFBs will be discussed. Therefore, the available ideas and approaches will be provided to direct further improvements in the power density and energy density of VFB systems.

Color-tunable emission and energy transfer investigation in Sr3Y(PO4)3:Ce3+,Tb3+ phosphors for white LEDs

A novel color-tunable phosphor Sr₃Y(PO₄)₃:Ce³⁺,Tb³⁺ was synthesized through solid-state reaction method. Several techniques, such as X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy, were used to investigate the obtained phosphors. Results of luminescence spectra and decay time measurements revealed that an efficient energy transfer occurred from Ce³⁺ to Tb³⁺ via a dipole-dipole mechanism, where Ce³⁺ exhibited a strong excitation band in the near-ultraviolet region. CIE chromaticity coordinates were tuned from deep blue (0.162, 0.090) to green (0.230, 0.411) by adjusting the relative concentrations between Ce³⁺ and Tb³⁺ ions. Results revealed that the as-synthesized phosphors had color-tunable characteristics and can be used as promising materials in the field of phosphor-converted white light-emitting diodes.

Synthesis, energy transfer and tunable emission properties of SrSb2O6:Eu(3+), Bi(3+) phosphor

Host SrSb2O6, SrSb2O6:Bi(3+), SrSb2O6:Eu(3+), and SrSb2O6:Eu(3+), Bi(3+) phosphors are synthesized by solid state reaction method in air. Host SrSb2O6 with excitation 254nm shows weak green-yellow emission in the range of 320-780nm due to Sb(5+)→O(2-) transition. SrSb2O6:Bi(3+) phosphor with excitation 365nm emits green light within the range 400-650nm owing to the (3)P1→(1)S0 transition of Bi(3+) ion. SrSb2O6:Eu(3+) phosphor with excitation 254nm exhibits a systematically varied hue from green to orange-red light by increasing Eu(3+) concentration from 0 to 7mol%, and that with excitation 394nm only shows orange-red light. The optimal Eu(3+) concentration is ~4mol% in SrSb2O6:Eu(3+) phosphor. SrSb2O6:Eu(3+), Bi(3+) phosphor with excitation 254 and 394nm emits orange-red light. Emission intensity of SrSb2O6:Eu(3+) phosphor may be enhanced >2 times by co-doping Bi(3+) ion because of the fluxing agent and energy transfer roles of Bi(3+) ion in SrSb2O6:Eu(3+), Bi(3+) phosphor. The luminous mechanism of SrSb2O6:Eu(3+), Bi(3+) phosphor is analyzed and explained by the simplified energy level diagrams of Sb2O6(2-) group, Bi(3+) and Eu(3+) ions, and energy transfer processes between them.

Tunable emission, energy transfer and charge compensation in Sr3(VO4)2:Sm(3+),P(5+),Na(+) phosphor

A series of Sr3(VO4)2:Sm(3+),P(5+),Na(+) phosphors are synthesized by using solid-state reaction method in air. The strongest emission band peaking at ∼600 nm is assigned to the (4)G5/2→(6)H7/2 transition of Sm(3+) ion, and the strong excitation peak at ∼402 nm due to (6)H5/2→(4)F7/2 transition indicates that these phosphors can be excited by near ultraviolet light emitting diode chip. Energy transfer (ET) between VO4(3-) group and Sm(3+) ion can be observed. Sr3(VO4)2:Sm(3+) phosphor with excitation 320 nm exhibits a systematically varied hues from green to yellow by changing Sm(3+) ion concentration from 0 to 6 mol%. The luminous mechanism of Sr3(VO4)2:Sm(3+) phosphor is explained by using the energy level diagrams of VO4(3-) group and Sm(3+) ion. The luminescence properties of Sr3(VO4)2:Sm(3+) phosphor can be improved and tuned by codoping the P(5+) and Na(+) ions due to ET and charge compensation. Lifetimes of Sr2.925Sm0.05(VO4)2, Sr2.925Sm0.05(V0.9P0.1O4)2, and Sr2.9Na0.05Sm0.05(V0.9P0.1O4)2 phosphors are 1.208, 1.219, and 0.796 ms, respectively. The experiment results are helpful to adjust the luminescence properties of Sm(3+)-doped other phosphors.

Tunable emission, energy transfer and charge compensation in SrMoO4:Sm(3+),Tb(3+),Na(+) phosphor

A series of SrMoO4:Sm(3+),Tb(3+),Na(+) phosphors was synthesized using a high-temperature solid-state reaction method in air. On excitation at 290 nm, SrMoO4:Sm(3+),Tb(3+) phosphor emitted light that varied systematically from green to reddish-orange on changing the Sm(3+) and Tb(3+) ion concentrations. The emission intensities of SrMoO4:Sm(3+) and SrMoO4:Sm(3+),Tb(3+) phosphors were increased two to four times due to charge compensation when Na(+) was added as a charge compensator. The luminescence mechanism and energy transfer could be explained using energy-level diagrams of the MoO4(2-) group, Sm(3+) and Tb(3+) ions. SrMoO4:Sm(3+),Tb(3+),Na(+) could be used as reddish-orange phosphor in white light-emitting diodes (LEDs) based on an ~ 405 nm near-UV LED chip. This research is helpful in adjusting and improving the luminescence properties of other phosphors.

Enhanced near-infrared emission by co-doping Ce3+ in Ba2Y(BO3)2Cl:Tb3+, Yb3+ phosphor

Ba₂Y(BO₃)₂Cl:Ce³⁺, Tb³⁺, Yb³⁺ with intense near-infrared emission and broad-band absorption in n-UV region is a promising down-conversion solar spectral convertor to enhance the efficiency of the silicon solar cells.

Synthesis, optical properties, and energy transfer of Ce(3+)/Tb(3+) co-doped MyGdFx (M=Li, Na, K)

Through a solid-state reaction method, the Ce(3+)/Tb(3+) co-doped MyGdFx (M=Li, Na, K; x=3, 4, 6; y=0, 1, 3) system samples have been synthesized by controlling the annealing temperatures and the ratios of raw materials. The samples were characterized by X-ray diffraction (XRD) patterns, photoluminescence (PL) excitation and emission spectra as well as luminescent dynamic decay curves. The experimental results suggest that the LiF is more difficult to react with the prepared material compared that of NaF or KF under similar reaction conditions. The samples crystallized in different crystalline phases. The energy transfer from Ce(3+) to Tb(3+) or Ce(3+) to Gd(3+) to Tb(3+) has been observed in all the samples. The Ce(3+) and Tb(3+) present different optical properties for they are sensitive to the local environment. In addition, the deduced lifetime of Tb(3+)(5)D4→(7)F5 transition decreases in the same system samples with the annealing temperature increasing. The deduced lifetime of Tb(3+)(5)D4→(7)F5 also decreases with the increase of the KF concentration in the KF system samples.

Sol-Gel Synthesis and Antioxidant Properties of Yttrium Oxide Nanocrystallites Incorporating P-123

Yttrium oxide (Y₂O₃) nanocrystallites were synthesized by mean of a sol-gel method using two different precursors. Raw materials used were yttrium nitrate and yttrium chloride, in methanol. In order to promote oxygen vacancies, P-123 poloxamer was incorporated. Synthesized systems were heat-treated at temperatures from 700 °C to 900 °C. Systems at 900 °C were prepared in the presence and absence of P-123 using different molar ratios (P-123:Y = 1:1 and 2:1). Fourier transform infrared spectroscopy (FTIR) results revealed a characteristic absorption band of Y–O vibrations typical of Y₂O₃ matrix. The structural phase was analyzed by X-ray diffraction (XRD), showing the characteristic cubic phase in all systems. The diffraction peak that presented the major intensity corresponded to the sample prepared from yttrium chloride incorporating P-123 in a molar ratio of P-123:Y = 2:1 at 900 °C. Crystallites sizes were determined by Scherrer equation as between 21 nm and 32 nm. Antioxidant properties were estimated by 2,2-diphenyl-1-picrylhydrazyl (DPPH•) assays; the results are discussed.