Elevating photoluminescence properties of Y3MgAl3SiO12:Ce3+ transparent ceramics for high-power white lighting

Compared with Y₃Al₅O₁₂:Ce³⁺,Y₃MgAl₃SiO₁₂:Ce³⁺(YMASG:Ce³⁺) reveals great potential for highpower white lighting with red-shift spectrum.Herein,YMASG:Ce³⁺ transparent ceramics were explored to be synthesized in the air following hot isostatic pressure(HIP) treatment to obtain tunable and optimized optical properties.Then phase purity,microstructure,transmittance,and photoluminescence of YM...     

Mechanical properties,thermophysical properties and electronic structure of Yb3+ or Ce4+-doped La2Zr2O7-based TBCs

First-principles calculations based on density functional theory were performed to investigate the cohesive energies, elastic modulus, Debye temperatures, thermal conductivities and density of states of La_2−xYb_xZr₂O₇, La₂Zr_2−xCe_xO₇ and La_2−xYb_xZr_2−xCe_xO₇ (x = 0.00, 0.25, 0.50, 0.75, 1.00) ceramics. The results show that doping Yb³⁺ or Ce⁴⁺ into La₂Zr₂O₇ reduces its elastic modulus, thermal conductivity and Debye temperature. Compared with La_2−xYb_xZr₂O₇ (x ≠ 0.00), La₂Zr_2−xCe_xO₇ compounds have better ductility and lower Debye temperature. The Debye temperature values of La₂Zr_2−xCe_xO₇ (x ≠ 0.00) compounds are in the range of 485.0–511.5 K. Among all components, the fluorite-type La_2−xYb_xZr_2−xCe_xO₇ (x = 0.75, 1.00) compounds exhibit better mechanical and thermophysical properties, and their thermal conductivity values are only 1.213–1.246 W/(m∙K) (1073 K), which are 14.5%–16.7% lower than that of the pure La₂Zr₂O₇. Thus, our findings open an entirely new avenue for TBCs.     

Energy transfer and luminescent properties of Tb3+ and Tb3+, Yb3+ doped CNGG phosphors

In this work,calcium niobium gallium garnet(Ca₃ Nb_1.6875Ga_3.1875O₁₂-CNGG) ceramic samples singledoped with Tb³⁺ and co-doped with Tb³⁺ and Yb³⁺ ions were sintered by the solid-state reaction method.The structural characterization of the samples was carried out by X-ray diffraction measurements.The optimal concentration of Tb³⁺ ions corresponding to the maximum luminescence in the green spectral range in CNGG:...     

Luminescence properties of a single-host phosphor Bal.8-wSrwLi0.4SiO4： cea＋,Eu2＋,Mn2＋ for WLED

In order to obtain a single-host-white-light phosphor,a series of Ba1.8-w-x-y-zSrwLi0.4-xCexEuyMnzSiO4(BSLS:Ce3+,Eu2+,Mn2+)powder samples were synthesized via high temperature solid-state reaction.The structure and photoluminescence properties were investigated.Under ultraviolet excitation,the emission spectra contained three bands:the 370-470 nm blue band,the 470-570 nm green band and the 570-700 nm red band,which arose from the 5d→4f transitions of Ce3+ and Eu2+,and the 4T1→6A1 transition of Mn2+,respectively.The excitation spectra of the emissions of Ce3+ and Mn2+ ions showed the energy transfer from Ce3+ to Mn2+.White light emission was obtained from the tri-doped samples of appropriate doping concentration under 310-360 nm excitation.     

Influence of A-site doping barium on structure,magnetic and microwave absorption properties of LaFeO3 ceramics powders

In this paper, the effect of Ba²⁺ ions A-site doping LaFeO₃ on structure, magnetic properties and microwave absorption properties was investigated by the sol–gel method. According to the TEM and FullProf refinement results, the structure of LaFeO₃ changes from orthogonal (SG: Pnma) to cubic (SG: Pm-3m) when the Ba doping amount is x = 0.4. The SEM image shows that the particles size tends to decrease with the increase of Ba content. The production of weak ferromagnetism indicates that Ba doping has a significant effect on the magnetic properties of LaFeO₃. The Neel temperature (T_N) decreases significantly with the increase of Ba doping amount. An appropriate amount of Ba doping can effectively increase the dielectric and magnetic loss of LaFeO₃ ceramics powders. The increase permittivity (ε′ and ε″) may be attributed to the hopping of the electrons between the Fe³⁺ and Fe⁴⁺ ions with the Ba²⁺ ions doping. The minimum reflection loss (RL_min) of La_0.9Ba_0.1FeO₃ at 6.72 GHz reaches ?30.04 dB, its effective bandwidth (RL ≤ ?10 dB) is 2.1 GHz, and the matching thickness is only 3.2 mm. These results indicate that Ba doping can effectively control the microwave absorption properties of LaFeO₃, especially in the C-band.     

Multicolor luminescence of hexagonal NaYF4:Yb3+/Ho3+/Ce3+ microcrystals with tunable morphology under 940 nm excitation for temperature-responsive anti-counterfeiting

In this study, the hexagonal NaYF₄:Yb³⁺/Ho³⁺/Ce³⁺ microcrystals were synthesized controllably, and upconversion luminescence excited at 940 nm and its application in temperature-responsive anti-counterfeiting are reported. It is clarified that the Ln³⁺ (Ln = Y + Yb + Ho + Ce) density ratio of bottom plane to side plane in the unit cell can be regulated by Ce³⁺ doping. It is also proved that the energy transfer of Yb³⁺ to Ho³⁺ is responsible for the activation of Ho³⁺ under 940 nm excitation, while the cross relaxation between Ho³⁺ and Ce³⁺ participates in the redistribution of electron population of ⁵S₂/⁵F₄ and ⁵F₅ levels. Both theory and experiment confirm that the intensity ratio of red to green emission (I_R/I_G) as a function of temperature as an independent variable has good linear characteristics in the temperature range of 300–500 K. Due to the good responsiveness of multicolor luminescence to temperature, the hexagonal NaYF₄:Yb³⁺/Ho³⁺/Ce³⁺ with tunable morphology is a promising candidate for advanced temperature-responsive upconversion anti-counterfeiting. Our results provide a new pathway for the controllable synthesis of hexagonal NaYF₄ microcrystals as well as the regulation of upconversion luminescence that is excited by wavelengths other than 980 nm and its application in anti-counterfeiting.     

Synthesis and characterization of YAG: Ce3+ fluorescence powders by co-precipitation method

YAG:Ce³⁺(Yttrium aluminum garnet) fluorescence powders were successfully prepared by co-precipitation method using aluminum nitrate, yttrium nitrate, cerous nitrate as the starting materials and ammonium carbonate as precipitant. The products were characterized by X-ray powder diffraction, luminescence spectrometer, transmission electron microscope (TEM). The XRD results showed that the obtained YAG:Ce³⁺ fluorescence powders had the crystalline structures of YAG at calcinations temperature of 900 °C and the TEM results showed that the grain diameters were about 100 nm. The YAG:Ce³⁺ fluorescence powders, synthesized by co-precipitation method, had the best luminescence property when the Ce doping amount was x=0.06 in the molecular formula of Y_3-xCe_xAl₅O₁₂, the calcinations time was 2 h and the calcinations temperature was 1000 °C.     

Structure and luminescence properties of color-tunable phosphor Sr2La3(SiO4)3F:Tb3+,Sm3+

A series of single-phase and color-tunable phosphors Sr₂La₃(SiO₄)₃F:0.15Tb³⁺,xSm³⁺(SLSOF:0.15Tb³⁺,xSm³⁺) was prepared using solid-state route.The X-ray diffraction(XRD) was used to characterize the phase of the as-prepared samples.The synthesized phosphors have apatite-type structure without other impurities.Sm³⁺ and Tb³⁺ ions substitute La³⁺ into the lattice and form a single...     

Synthesis and optical properties of novel apatite-type NaCa3Bi(PO4)3F:Dy3+ yellow-emitting fluorophosphate phosphors for white LEDs

In this study, novel yellow-emitting fluorophosphate NaCa₃Bi(PO₄)₃F phosphors doped with different concentrations of Dy³⁺ ions were first obtained via high-temperature solid-state reaction. The crystal structure, phase purity, particle morphology, photoluminescence (PL) properties, thermal stability, and luminescence decay curves of the resulting phosphors were then characterized in detail. Under the excitation of 349 nm, the three dominant peaks of the NaCa₃Bi(PO₄)₃F:Dy³⁺ are centered at 480 nm (⁴F_9/2-⁶H_15/2), 577 nm (⁴F_9/2-⁶H_13/2), and 662 nm (⁴F_9/2-⁶H_11/2). The optimal doping concentration of Dy³⁺ ions in the NaCa₃Bi(PO₄)₃F:xDy³⁺ phosphors is x = 5 mol%. The phosphors show excellent thermal stability with high activation energy (E_a = 0.32 eV). Eventually, the synthesized white light-emitting diode (w-LED) demonstrates the Commission International de L'Eclairage (CIE) chromaticity coordinates of (0.341, 0.334), a good correlated color temperature (CCT) of 5083 K, and a high color rendering index (R_a) of 92. Revealing its potential as yellow-emitting phosphors, the feasibility of the fabricated apatite-type NaCa₃Bi(PO₄)₃F:Dy³⁺ fluorophosphate phosphors was confirmed for w-LEDs.     

Physicochemical properties of Li3Ba2La3(MoO4)8:Eu,Tb red-emitting phosphor for solid state white lamps

In this work,combustion synthesis was used for the first time to fabricate a phosphor material with red emission for applications in solid-state white-light lamps.We synthesized a material with emission wavelength at λ_em=617 nm,excited under long UV-blue wavelength based on Eu³⁺,Tb³⁺-activated molybdates Li₃Ba₂(La_1-x-yEu_xTb_y)₃(MoO₄)₈ with 0 ≤ x ≤1 and 0 ≤ y ≤ 1.A series of pow...     

Doping effect of rare earth metal ions Sm3+, Nd3+ and Ce4+ on denitration performance of MnOx catalyst in low temperature NH3-SCR reaction

The MnXO_x catalysts(i.e.,MnSmO_x,MnNdO_x,MnCeO_x) were prepared by reverse co-precipitation method and used for NH₃-SCR reaction.It is found that MnCeO_x catalyst presents the best low tempe rature catalytic activity(higher than 90% NO_x conversion in the te mperature range from 125 to 225℃)and excellent H₂O+SO₂ resistance.In order to explore the reason for this result,the characterization of X-ray diff...     

Ce3+ sensitized Tb3+ and Dy3+ photoluminescence in β-LaB5O9 prepared by sol–gel method

Rare earth (RE) pentaborates, both α- and β-polymorphs, are good candidates for photoluminescent hosts suitable for various RE activators. Ce³⁺ acts not only as an activator itself, but also as a sensitizer to other rare earth activators, like in the case of commercial green phosphor CeMgAl₁₁O₁₉:Tb³⁺. In this work, two solid solutions of β-La_0.9–xCe_0.1Tb_xB₅O₉ (0 ≤ x ≤ 0.15) and β-La_0.9–yCe_0.1Dy_yB₅O₉ (0 ≤ y ≤ 0.07) were prepared by sol–gel method with high crystallinity, and the phase purity was confirmed with careful analyses on powder X-ray diffraction patterns. Energy transfers are expected due to the overlapping of Ce³⁺ emission with the Tb³⁺/Dy³⁺ excitation. Indeed, the steady photoluminescence spectra indicate the decrease of the Ce³⁺ emission and the increase of the Tb³⁺/Dy³⁺ emission, and the fluorescence decay curves exhibit the decrease of the average lifetime of Ce³⁺. The energy transfer efficiency is estimated to be 60% at x = 0.15 and 55% at y = 0.07, respectively. The mechanism is likely through the dipole–dipole electric interactions for both cases. With this rationale, the Tb³⁺ and Dy³⁺ emissions are greatly enhanced, in particular, the white emission of Dy³⁺ in β-La_0.85Ce_0.1Dy_0.05B₅O₉ is enhanced by 20 times.     

Effects of Er3+ doping on structure and thermal properties of (Sm1–xErx)2Zr2O7 ceramics for thermal barrier coating

Rare earth Er³⁺ doped (Sm_1–xEr_x)₂Zr₂O₇ (x = 0.1, 0.2, and 0.3) ceramic samples were synthesized using a solid state reaction method. The microstructure and thermal properties of these ceramics were investigated to evaluate their potential as thermal barrier coating materials. The results show that ceramics are compact with regular-shaped grains of 1–5 μm size. (Sm_1–xEr_x)₂Zr₂O₇ has a pyrochlore structure mainly determined by ionic radius ratio, but the ordering degree decreases with increase of the Er₂O₃ content. There is no phase transformation from 1000 to 1200 °C, and the (Sm_1–xEr_x)₂Zr₂O₇ ceramics exhibit excellent phase stability during thermal treatment at 1200 °C for 100 h and 1400 °C for 50 h. The thermal conductivities of dense (Sm_1–xEr_x)₂Zr₂O₇ ceramics range from 1.52 to 1.59 W/(m·K), which is lower than that of Sm₂Zr₂O₇, and decrease as the Er₂O₃ content increases. Besides, the thermal expansion coefficient of (Sm_1–xEr_x)₂Zr₂O₇ is higher than that of Sm₂Zr₂O₇.     

A novel Gd-based phosphor NaGdGeO4:Bi3+,Li+ with super-long ultraviolet-A persistent luminescence

In very recent years,ultraviolet(UV) persistent luminescent materials(PLMs) have attracted widespread attention due to their potential biological applications.However,owing to the lack of suitable emitters and hosts,the design and development of excellent UV PLMs remain challenging.Here,we report a new Gd-based PLM NaGdGeO₄:Bi³⁺ with super-long UVA persistent luminescence(PersL).By further codoping Li⁺ ions to increase the concentration of traps,the UVA PersL int...     

Tunable emission,energy transfer and thermal stability of Ce3+, Tb3+ co-doped Na2BaCa(PO4)2 phosphors

A series of single Ce³⁺ doped and Ce³⁺ and Tb³⁺ co-doped Na₂BaCa(PO₄)₂ (NBCP) phosphors was synthesized by conventional solid-stated reaction method. The crystal structure, luminescence properties, thermal stability and energy transfer were carefully investigated. Ce³⁺ is inferred to substitute the Ba²⁺ site in NBCP lattice. The color-tunable emission from blue to green is observed by adjusting Tb³⁺ concentration among NBCP:0.03Ce³⁺,yTb³⁺ phosphors. The energy transfer behavior from Ce³⁺ to Tb³⁺ ions is both illustrated by co-doped PL spectra and decay curves. The energy transfer efficiency is as high as 91.5%. The mechanism of energy transfer is resonance type of dipole-dipole transition. In this work, the optimal phosphor exhibits the excellent thermal stability which keeps at 94.9% of that initial value at room temperature when temperature reaches to 150 °C. The Ce³⁺ and Tb³⁺ co-doped NBCP phosphor is a promising candidate for the application in the general lighting and display fields.     

Ln3+ (Ln = Eu,Dy) - doped Sr2CeO4 fine phosphor particles: Wet chemical preparation,energy transfer and tunable luminescence

The Sr₂CeO₄:Ln³⁺ (Ln = Eu, Dy) fine phosphor particles were prepared by a facile wet chemical approach, in which the consecutive hydrothermal-combustion reaction was performed. The doping of Ln³⁺ into Sr₂CeO₄ has little influence on the structure of host, and the as-prepared samples display well-crystallized spherical or elliptical shape with an average particle size at about 100–200 nm. For Eu³⁺ ions-doped Sr₂CeO₄, with the increase of Eu³⁺-doping concentration, the blue light emission band with the maximum at 468 nm originating from a Ce⁴⁺ → O²⁻ charge transfer of the host decreases obviously and the characteristic red light emission of Eu³⁺ (⁵D₀→⁷F₂ transition at 618 nm) is enhanced gradually. Simultaneously, the fluorescent lifetime of the broadband emission of Sr₂CeO₄ decreases with the doping of Eu³⁺, indicating an efficient energy transfer from the host to the doping Eu³⁺ ions. The energy transfer efficiency from the host to Eu³⁺ was investigated in detail, and the emitting color of Sr₂CeO₄:Eu³⁺ can be easily tuned from blue to red by varying the doping concentration of Eu³⁺ ions. Moreover, the luminescence of Dy³⁺-doped Sr₂CeO₄ was also studied. Similar energy transfer phenomenon can be observed, and the incorporation of Dy³⁺ into Sr₂CeO₄ host leads to the characteristic emission of ⁴F_9/2 → ⁶H_15/2 (488 nm, blue light) and ⁴F_9/2 → ⁶H_13/2 (574 nm, yellow light) of Dy³⁺. The Sr₂CeO₄:Ln³⁺ fine particles with tunable luminescence are quite beneficial for its potential applications in the optoelectronic fields.     

Luminescent ionic lattice occupation and wide tunable emission spectra of La2MgZrO6:Bi3+,Eu3+ double perovskite phosphors for white light LED

La₂Mg_1-x/2Zr_1-x/2O₆:xBi³⁺(x=0.01-0.035,abbreviated as LMZ:Bi³⁺) and La_2-yMg_0.99Zr_0.99O₆:0.02Bi³⁺,yEu³⁺(y=0.1-0.11,abbreviated as LMZ:Bi³⁺,Eu³⁺) double-perovskite phosphors were prepared through high-temperature solid-phase method.The emission spectrum of LMZ:xBi³⁺(x=0.01-0.035)phosphors excited at 353 nm is asymmetric in the range be...     

Effective regulation of electronic structures and luminescence properties of LiGd9(SiO4)6-x(GeO4)xO2:Dy3+ phosphors by tetrahedral substitution

A series of Dy³⁺-activated phosphors with the general formula LiGd₉(SiO₄)_6-x(GeO₄)_xO₂:Dy₃₊(0 ≤ x≤ 3)characterized by an apatite-type structure were successfully synthesized via a simple solid-state technique involving a partial substitution of [SiO₄]^4-with [GeO₄]^4- species.The effects of homovalent[GeO₄]^4--[SiO₄]^4- substit...     

LiY1-xEux（MoO4）2 as a promising red-emitting phosphor of WLEDs synthesized by sol-gel process

A series of LiY1-xEux(MoO4)2 red-emitting phosphors were synthesized by sol-gel technique. The phase impurity and spectroscopic properties were characterized by X-ray diffraction (XRD) and photo-luminescence (PL) spectra respectively. The effect of Eu3+ doping con-centration, annealing temperature and the molar ratio of citric acid to the total metal cations (C:M) on the optical properties of the red phos-phors were studied and optimized. It was found that all the samples could be excited efficiently by blue light (465 nm), which was well coin-cident with the emission of GaN based LED chips. The luminescent intensity reached maximum when annealing temperature was 750 ?C and Eu3+ doping concentration was 5% with C:M=3:1.     

Insights into structural and spectroscopic characterization of Sm3+ doped orange rich red emitting CsMgPO4 phosphors

In the present study, Sm³⁺ activated inorganic orthophosphate CsMgPO₄ (CSMP) phosphors were prepared by adopting a solid-state reaction method. The structural phase purity and morphological features were studied by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM), respectively. The molecular structure and vibrational modes were substantiated with the Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy characterization. The optical bandgap of the host and Sm³⁺ doped phosphors was deduced from the diffused reflectance (DR) spectra with a typical value of 5.72 eV and a small variation is observed with increasing concentrations. A systematic study of photoluminescence (PL) properties of Sm³⁺ doped CSMP phosphors was carried out. From the room temperature excitation and emission spectra, it is found that the phosphor emits in the orange rich red light under the suitable excitation of 402 nm in the UV region and concentration quenching occurs at x = 0.02 doping level. The emission peaks observed at around 562, 598 and 644 nm confirm the characteristic Sm³⁺ 4f-4f transitions. The temperature-dependent photoluminescence (TD-PL) of the x = 0.02 (optimum doping) is recorded from 30 to 210 °C, showing good thermal stability even at 150 °C. The thermal quenching mechanisms are discussed based on the configuration coordinate model of excitation and emission. The prepared phosphors are found to exhibit near thermal stability compared to the commercially available red phosphors. PL decay time and quantum efficiency were measured. The colour coordinates are found to lie in the orangish-red region of the colour space. Thus the prepared phosphors CSMP:x Sm³⁺ can be useful as a red component in designing UV excitable chip-based phosphor-converted white LED applications.