Thermally stable double perovskite CaLaMgSbO6:Eu3+ phosphors as a tunable LED-phosphor material

A series of Eu³⁺ ions activated double perovskite CaLaMgSbO₆ phosphors were successfully synthesized. Crystal structure was investigated by XRD and the results showed that this double perovskite exhibited rock-salt ordering of B-site ions. High-resolution transmission electron microscopy was used to prove the existence of B-site ordering. Thereafter, luminescence properties of the as-prepared powders were discussed in detail. The phosphors could be well excited by ultraviolet, near ultraviolet, and blue light. The quenching concentration for the transition of ⁵D₀-⁷F₂ reached up to 50.0 mol%. The theoretical quenching concentration and quenching mechanism were discussed in detail. Excellent thermal stability of this double perovskite phosphor was obtained and the quenching mechanism was investigated based on the configurational coordinate diagram. The CIE coordinates showed that this double perovskite phosphor had great potential in solid state lighting.     

Synthesis of Ca2SiO4:Dy3+ phosphors from agricultural waste for solid state lighting applications

Trivalent dysprosium (Dy³⁺) ions -doped calcium silicate (Ca₂SiO₄) phosphors have been synthesized by utilizing agricultural waste of egg shell and rice husk through solid-state reaction method. The synthesized Ca₂SiO₄ powders thus obtained are crystallized in monoclinic structure with unit cell parameters of a = 5.53 Å; b = 6.67 Å; c = 9.13 Å; β = 87.43° and irregular shape morphology. Luminescent properties of Dy³⁺:Ca₂SiO₄ phosphors were studied by varying active ion concentration. The phosphors emit characteristic blue and yellow emissions of Dy³⁺ ions corresponding to the ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions, respectively. Color coordinates evaluated from emission spectra are found to fall in the white light region. Decay curves for the ⁴F_9/2 level of Dy³⁺ ions exhibit single exponential nature and turn into non-exponential with shortening of lifetime from 739 µs to 510 µs when Dy³⁺ ion concentration is increased from 0.001 to 0.5 mol%. All these results confirm that Ca₂SiO₄:Dy³⁺ phosphors are suitable for the use as low cost white light emitting phosphors.     

Synthesis and photoluminescence enhancement of Ca3Sr3(VO4)4:Eu3+ red phosphors by co-doping with La3+

In this study, a series of red-emitting Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphors co-doped with La³⁺ was prepared using the combustion method. The microstructures, morphologies, and photoluminescence properties of the phosphors were investigated. All Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ samples synthesized at temperatures greater than 700 ℃ exhibited the same standard rhombohedral structure of Ca₃Sr₃(VO₄)₄. Furthermore, the Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ phosphor was effectively excited by near-ultraviolet light of 393 nm and blue light of 464 nm. The strong excitation peak at 464 nm corresponded to the ⁷F₀→⁵D₂ electron transition of Eu³⁺. The strong emission peak observed at 619 nm corresponded to the ⁵D₀→⁷F₂ electron transition of Eu³⁺. Co-doping with La³⁺ significantly improved the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺ red phosphors. The optimum luminescence of the phosphor was observed at Eu³⁺ and La³⁺ concentrations of 5% and 6%, respectively. Moreover, co-doping with La³⁺ also improved the fluorescence lifetime and thermal stability of the Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphor. The CIE chromaticity coordinate of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ was closer to the NTSC standard for red phosphors than those of other commercial phosphors; moreover, it had greater color purity than that of all the samples tested. The red emission intensity of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ at 619 nm was ~1.53 times that of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺ and 2.63 times that of SrS:Eu²⁺. The introduction of charge compensators could further increase the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ red phosphors. The phosphors synthesized herein are promising red-emitting phosphors for applications in white light-emitting diodes under irradiation by blue chips.     

Gd3Al3Ga2O12:Ce,Mg2+ transparent ceramic phosphors for high-power white LEDs/LDs

Gd₃Al₃Ga₂O₁₂:1.5%Ce, xMg²⁺ (GAGG:1.5%Ce, xMg²⁺) transparent ceramic phosphors (TCPs) were prepared via a two-step sintering method. The effects of MgO on microstructures and luminescent properties of GAGG:Ce TCPs are investigated for the first time. For the optimized Mg²⁺ of x = 0.5%, the in-line transmittance of the obtained TCP reaches 78.6%. Performances of the titled TCPs in high-power light-emitting diodes (LEDs) and laser diodes (LDs) lighting are illustrated. The optimized TCP shows the luminous efficacy of 84.0 lm W^?1 in LD lighting. This work provides a strategy to modify TCPs for the next-generation LD lighting.     

Synthesis of high efficiency Zn2SiO4:Mn green phosphors using nano-particles

In this study, Zn₂SiO₄:Mn²⁺ luminescent phosphors were prepared by mixing nano-scale ZnO, SiO₂, and MnO₂ particles at the compositions corresponding to 2ZnO + SiO₂ + X mol% MnO₂ (Zn₂SiO₄–X-MnO₂, 0.02 ≤ X ≤ 0.05). The mixing powders were calcined from 900 °C to 1300 °C in air and in N₂ atmosphere. No matter calcined in air or in N₂ atmosphere, Zn₂SiO₄ was the mainly crystalline phase in particles calcined at 900 °C and was the only phase in particles calcined at 1000 °C and higher. The influences of MnO₂ concentration and calcining atmosphere and temperature on wavelength of luminescence peak and the emission intensity were further intensively investigated. We would show that the calcining atmosphere had no apparent influences on the physical and photoluminescence (PL) characteristics of Zn₂SiO₄:Mn²⁺ phosphors. The MnO₂ content and the calcining temperature were the main reasons to influence the physical and PL characteristics of Zn₂SiO₄:Mn²⁺ phosphors.     

Sol-gel synthesis and luminescence properties of Ba2SiO4:Sm3+ nanostructured phosphors

Ba₂SiO₄:Sm³⁺ nanostructure phosphors have been synthesized by a simple sol-gel method. Phase evaluation, structural characteristics and photoluminescence properties of the synthesized Ba₂SiO₄:Sm³⁺ powders were studied using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FTIR), and photoluminescence spectroscopy (PL). X-ray diffraction results showed that all synthesized samples were single-phase barium silicate (Ba₂SiO₄) and samarium (Sm) ions were incorporated into the lattice of Ba₂SiO₄. Adding samarium to barium silicate changed the microstructure from vermicular to spherical structures. The Photoluminescence spectrum of Ba₂SiO₄:Sm³⁺ phosphors exhibited characteristic emission peaks at 562?nm which is due to the ⁴G_{5/2 →}⁶H_7/2 transition of samarium ions and corresponds to the orange region. The results showed that the barium silicate activated with 0.08?mol samarium exhibited the highest PL intensity.     

Cathodoluminescence and thermoluminescence of ZnB2O4:Eu3+ phosphors prepared via wet-chemical synthesis

In present work, a series of Eu doped zinc borate, ZnB₂O₄, phosphors prepared via wet chemical synthesis and their structural, surface morphology, cathodoluminescence (CL) and thermoluminescence (TL) properties have been studied. Phase purity and crystal structure of as-prepared samples are confirmed by X-ray diffraction measurements (XRD) and they were well consistent with PDF card No. 39-1126, indicating the formation of pure phase. The thermoluminescence (TL) behaviors of Eu activated ZnB₂O₄ host lattice are studied for various beta doses ranging from 0.1 to 10?Gy. The high-temperature peak of Eu activated sample located at 192?°C exhibited a linear dose response in the range of 0.1–10?Gy. Initial rise (IR) and peak shape (PS) methods were used to determine the activation energies of the trapping centres. The effects of the variable heating rate on TL behaviour of Eu activated ZnB₂O₄ were also studied. When excited using an electron beam induced light emission (i.e cathodoluminescence, CL) at room temperature (RT), the as-prepared phosphors generate reddish-orange color due to predominant emission peaks of Eu³⁺ ions located at 576–710?nm assigned to the ⁵D₀→⁷F_J (J=1,2,3, and 4) transitions. The maximum CL intensity for Eu³⁺ ions at 614?nm with transition ⁵D₀→⁷F₂ was reached Eu³⁺ concentration of 5?mol%; quenching occurred at higher concentrations. Strong emission peak for Eu³⁺ ions at 614?nm with transition ⁵D₀→⁷F₂ is observed. The CL experimental data indicate that ZnB₂O₄:Eu³⁺ phosphor as an orange-red emitting phosphor may be promising luminescence materials for the optoelectronic applications.     

红色荧光粉CaWO4:Eu3+,Gd3+的合成及其发光性能的研究

利用高温固相法合成了CaWO4:Eu3+,Gd3+红色荧光粉,通过X射线衍射、X射线光电子能谱和荧光光谱等对该荧光粉进行了表征。结果表明,CaWO4:Eu3+,Gd3+的荧光强度明显高于CaWO4:Eu3+,钆离子的最佳掺杂量为0.04。同时说明了钆离子引入到CaWO4:Eu3+中对其发光性能影响的机理以及不同浓度的钆对发光强度的影响。     

Effects of argon sintering atmosphere on luminescence characteristics of Ca6BaP4O17:Sm3+ phosphors

In this paper, Ca₆BaP₄O₁₇:Sm³⁺ and Li⁺ co-doped Ca₆BaP₄O₁₇:Sm³⁺ phosphors were synthesized in air and argon atmospheres using a solid-state reaction method. The phosphor morphologies and crystal structure were studied using scanning electron microscopy and X-ray diffraction, respectively. The emission and absorption characteristics were investigated using photoluminescence emission spectroscopy and diffuse reflectance spectroscopy. The surface states and composition of phosphor were investigated using X-ray photoelectron spectroscopy. The emission integrated intensities of the phosphors sintered in an argon atmosphere increased 3.5 fold than the ones sintered in air atmosphere, with Li⁺ ions becoming embedded in the lattice of the Ca₆BaP₄O₁₇:Sm³⁺ phosphor. This occurs because there are fewer defect/oxygen vacancies and less of the secondary phase forms, leading to better Sm³⁺ emission. The results suggest that sintering a mixture of the raw materials of a phosphor in an argon atmosphere is a good approach for synthesizing Ca₆BaP₄O₁₇:Sm³⁺ phosphor powders. The color purity and CIE values of an optimized phosphor sample sintered in an argon atmosphere with an Li⁺ ion compensator were calculated to be ~ 99.6% and (0.612,0.386) in the orange–red region under 405-nm excitation, respectively. Moreover, the solid solubility of Sm³⁺ ions in the Ca₆BaP₄O₁₇ host can be enhanced by using an argon atmosphere in the synthesis process.     

Effects of In2O3 nanoparticles doping on the photoluminescent properties of Eu2+/Eu3+ ions in silica glasses

Eu²⁺/Eu³⁺ ions doped silica glasses contained In₂O₃ nanoparticles (NPs) have been fabricated by using nanoporous silica glasses. Interestingly, efficient energy transfer from In₂O₃ NPs to Eu²⁺/Eu³⁺ ions enhanced the photoluminescence (PL) emission of Eu²⁺/Eu³⁺ ions, which derives from lattice defects in In₂O₃ NPs. Our work has not only demonstrated a facile way to fabricate NPs and rare earth ions co-doped silica glasses, but also extended the applications of semiconductor oxide NPs such as In₂O₃ NPs.     

Modification of Optical Properties of SrAl_2O_4：Eu~（2＋）,Dy~（3＋） Phosphor by Terbium Doping

以尿素为燃料,采用快速燃烧法在650℃合成了Tb3＋掺杂的SrAl2O4：Eu2＋,Dy3＋新型长余辉光致发光材料。研究了Tb3＋掺杂对Eu2＋,Dy3＋共激活的铝酸盐长余辉发光材料的发光特性的影响。X射线衍射分析结果表明：当Tb3＋的掺杂量x=0.17%时,合成的样品结构为单相SrAl2O4单斜晶系。光致发光测试结果表明：样品的激发光谱为峰值位于345nm附近的连续宽带谱,发射光谱为峰值位于510nm左右的连续宽带谱。余辉衰减曲线结果表明：Tb3＋的适量掺杂可以提高铝酸锶的余辉性能。与SrAl2O4：Eu2＋,Dy3＋相比,掺杂Tb3＋有利于形成结晶度良好的固溶体,样品中的晶体细密紧凑,颗粒粒径约为100nm。     

Enhanced upconversion study of Er3+-Yb3+ codoped NaYF4 phosphors synthesized by the reverse microemulsion method

Herein, nanocrystals of Er³⁺ and Er³⁺, Yb³⁺ co-doped NaYF₄ upconversion (UC) phosphor were prepared via the reverse-microemulsion method. The impact of different concentrations of Er³⁺ ions on the UC emission intensity after 980?nm diode laser excitation is discussed. The structure, morphology and composition of the nanophosphors were confirmed by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and the results showed the presence of NaYF₄ nanocrystals with hexagonal phases of NaYF₄. The UC spectra revealed two emission bands including a green and a red emission band and the CIE coordinate for the samples were estimated. The present research revealed that the reverse-microemulsion approach will be suitable for the synthesis of efficient upconversion nanophosphors.     

Improvement of photoluminescence properties of Ce3+- doped CaSrAl2SiO7 phosphors by charge compensation with Li+ and Na+

In this work, we prepared CaSr_1-xAl₂SiO₇:xCe³⁺ (0.03 ≤ x ≤ 0.12) and CaSr_0.94Al₂SiO₇:0.03Ce³⁺,0.03 M⁺ (M⁺ = Li⁺ and Na⁺) phosphors via solid-state reaction method. Structural and photoluminescence (PL) properties of the phosphors were also investigated. The prepared phosphors formed an orthorhombic crystal structure with the P2₁2₁2₁ space group. CaSr_1-xAl₂SiO₇:xCe³⁺ phosphors were effectively excited by near-ultraviolet (UV) light (345 nm), which is suitable with the emission of near-UV light emitting diode chips. A broad blue emission (402 nm) was detected in CaSr_1-xAl₂SiO₇:xCe³⁺ and CaSr_0.94Al₂SiO₇:0.03Ce³⁺,0.03 M⁺ phosphors; this was attributed to the 4f⁰5d¹ → 4f¹ transition of Ce³⁺. To maintain charge equilibrium, charge compensators, such as monovalent Li⁺ and Na⁺ ions, were doped into the CaSr_0.97Al₂SiO₇:0.03Ce³⁺ phosphor, significantly improving its PL properties. The strongest emission intensity was achieved in CaSr_0.94Al₂SiO₇:0.03Ce³⁺,0.03Li⁺ phosphor. Addition of Li⁺ charge compensator was highly effective in improving PL properties of CaSr_0.97Al₂SiO₇:0.03Ce³⁺ phosphors.     

Synthesis and spectroscopic analysis of Sm3+ doped CeO2 ceramic powders for the application of white LEDs

Orange-red light-emitting Sm³⁺-doped cerium oxide (CeO₂) ceramic powder with various concentrations of Sm³⁺ ions was prepared through a sol-gel process. X-ray diffraction and Rietveld analysis confirmed the formation of a purely cubic structure with a space group of $\mathit{Fm}\stackrel{?}{3}m$. The lattice parameters and unit cell volumes of the CeO₂:Sm³⁺ powder increased with the concentration of Sm³⁺ ions. The energy-dispersive X-ray spectra and corresponding mapping images confirmed the elemental composition and adequate dispersion of all elements in the CeO₂:Sm³⁺ powder. A broad excitation band at approximately 365?nm was observed in the excitation spectra of CeO₂:Sm³⁺ phosphors owing to the charge transfer transition from O 2p to Ce 4f orbitals. The Sm³⁺ doped CeO₂ phosphors emitted sharp luminescence with a main peak at 615?nm under excitation at 360?nm. The spectral analysis revealed that the CeO₂:Sm³⁺ phosphors exhibited strong orange-red emission. Concentration quenching was observed in the CeO₂:Sm³⁺ phosphors with 0.5?mol% of critical concentration of Sm³⁺ ions due to dipole dipole interaction of two nearest Sm³⁺ ions. The quantum efficiency was observed as high as 58%. The thermal stability of the present materials was estimated with the evaluation of activation energy as 0.31?eV. The broad excitation band and sharp orange–red emission indicated the potential use of CeO₂:Sm³⁺ phosphors for white light-emitting diodes.     

Alkali metal ion substitution induced luminescence enhancement of NaLaMgWO6:Eu3+ red phosphor for white light-emitting diodes

Alkali metal ion substitution is an effective strategy to improve the luminescence properties of phosphors. In this work, a series of red-emitting phosphors Na_1-xLi_x/2K_x/2La_0.6Eu_0.4MgWO₆ were prepared by a traditional high-temperature solid-state reaction. Their phase structure, microstructure, luminescence properties and potential application in phosphor-converted white light-emitting diodes (pc-WLEDs) were investigated in detail. X-ray diffraction (XRD) result revealed the formation of a solid solution when x?≤?0.3, which kept monoclinic structure of NaLaMgWO₆. Photoluminescence investigation indicated that the partial substitution of Li⁺/K⁺ ions for Na⁺ ions improved largely the red emission of Eu³⁺. Based on the optimized Na_0.7Li_0.15K_0.15La_0.6Eu_0.4MgWO₆ sample with relatively good thermal stability, a WLED device was fabricated by combining a near-ultraviolet (NUV) chip (~400?nm) with the phosphor mixture of commercial green/blue phosphors and the optimized red phosphor. The results indicated that the optimized red phosphor in this work could be a potential candidate for WLEDs pumped by NUV chips.     

光照对Sr4Al14O25：Eu^2＋，Dy^3＋／TiO2-xNx复合材料光催化性能的影响

采用溶胶-凝胶法制备出Sr4Al14O25：Eu^2＋,Dy^3＋／TiO2-xNx复合材料。该复合材料对甲基橙具有较高的光催化效果,复合材料经紫外激发后,其光催化效果高于没有经紫外激发的复合材料的光催化效果,而且明显高于Sr4Al14O25：Eu^2＋,Dy^3＋／TiO2-xNx光照激发后光催化效率之和,同时讨论了Sr4Al14O25：Eu^2＋,Dy^3＋／TiO2-xNx复合材料的光催化机理。     

Morphological,spectroscopic and photocatalytic properties of Eu3+:TiO2 synthesized by solid-state and hydrothermal-assisted sol-gel processes

Eu³⁺ doped TiO₂ powders were synthesized by solid-state reaction and hydrothermal-assisted sol-gel process. They were characterized by X-ray diffraction, scanning electron microscopy and photoluminescence techniques. Both synthetic procedures yield the pure anatase phase of titania. The excitation and emission spectra and the decay profiles were measured for different thermal treatments of the samples, in order to investigate the effects of the synthesis conditions on the doping mechanism. The photocatalytic activity was investigated by measuring the degradation of methylene blue under UV light irradiation and a correlation between its efficiency and the luminescence performance has been proposed.     

PEG对燃烧合成CaAl2O4:Eu2+,Nd3+长余辉发光材料的影响

采用燃烧法合成了CaAl2O4:Eu2+,Nd3+长余辉发光材料,研究了PEG(聚乙二醇)对其发光性能的影响。采用X-射线衍射(XRD)、荧光光谱对发光材料进行了表征。结果表明,燃烧产物主晶相为单斜晶系的CaAl2O4;PEG的添加有效提高了CaAl2O4:Eu2+,Nd3+长余辉发光材料的初始亮度,但余辉时间没有得到延长。     

Color-tunable properties based on complex anion substitution in Eu2+ doped Ca8Sc2(PO4)6-y(SiO4)1+y phosphor

We synthesized and investigated the effect of Eu²⁺ ions doping in a novel phosphor-silicate Ca₈Sc₂(PO₄)₆(SiO₄) phosphor. The structure and photoluminescence properties were determined by X-ray powder diffraction Rietveld refinement, diffuse reflection spectra, emission-excitation spectra, decay curves and temperature dependence spectra. The phosphors showed an asymmetric broad-band blue emission (Eu²⁺) with peak at 470?nm. Furthermore, we presented the Ca_7.96Sc₂(PO₄)_6-y(SiO₄)_1+y:0.04Eu²⁺ phosphors by co-substituting [Eu²⁺-Si⁴⁺] for [Ca²⁺-P⁵⁺], and different behaviors of luminescence evolution in response to structural variation were verified among the series of phosphors. The results were attributed to the presence of multi Ca²⁺ sites, resulting in the mixing of blue and green emissions for Eu²⁺ ions. The complex anion substitution of [PO₄]^3- by [SiO₄]^4- induced an increased crystal field splitting of the Eu²⁺ ions, which caused a decrease in emission energy from the 5d excited state to the 4f ground state and a resultant red-shift from 470?nm to 520?nm. All the properties indicated that the Ca₈Sc₂(PO₄)₆(SiO₄):Eu²⁺ phosphors have potential application for color-tunable WLEDs.     

Investigation on the anti-reduction mechanism of Ti4+ in high dielectric constant system Ca0.9La0.067TiO3 by doping with Al2O3

Ca_0.9La_0.067TiO₃ (abbreviated as CLT) ceramics doped with different amount of Al₂O₃ were prepared via the solid state reaction method. The anti-reduction mechanism of Ti⁴⁺ in CLT ceramics was carefully investigated. X-ray diffraction (XRD) was used to analyze the phase composition and lattice structure. Meanwhile, the Rietveld method was taken to calculate the lattice parameters. X-ray photoelectron spectroscopy (XPS) was employed to study the valence variation of Ti ions in CLT ceramics without and with Al₂O₃. The results showed that Al³⁺ substituted for Ti⁴⁺ to form solid solution and the solid solubility limit of Al³⁺ is near 1.11 mol%. Furthermore, the reduction of Ti⁴⁺ in CLT ceramics was restrained by acceptor doping process and the Q × f values of CLT ceramics were improved significantly. The CLT ceramic doped with 1.11 mol% Al₂O₃ exhibited good microwave dielectric properties: ε_r = 141, Q × f = 6848 GHz, τ_f = 576 ppm/°C.