Synthesis and luminescence properties of CaAl2O4:Mn4+ phosphor

CaAl_2−yO₄:yMn⁴⁺ (y = 0–1.6 mol%) phosphors are synthesized by a solid-state reaction method in air, and their crystal structure and luminescence property are investigated. To compare luminescence property, CaAl_3.99O₇:1%Mn⁴⁺ and SrAl_1.99O₄:1%Mn⁴⁺ phosphors are also synthesized at the same condition. Broad band excitation spectra are observed within the range 220–550 nm, and emission spectra cover from 600 to 720 nm with the strongest emission peak at ∼658 nm owing to the ²E → ⁴A₂ transition of Mn⁴⁺ ion. The influence of crystal field to luminous intensity is discussed, and the possible luminous mechanism of Mn⁴⁺ ion is explained by using energy level diagram of Mn⁴⁺ ion. CaAl_1.99O₄:1%Mn⁴⁺, CaAl_3.99O₇:1%Mn⁴⁺, and SrAl_1.99O₄:1%Mn⁴⁺ phosphors under excitation 325 nm light emit red light, and their CIE chromaticity coordinates are (0.7181, 0.2813), (0.7182, 0.2818), and (0.7198, 0.2801), respectively. These contents in the paper are helpful to develop novel and high-efficient Mn⁴⁺-doped phosphor for white LEDs.     

Synthesis and luminescence properties of Na+, Li+ compensated Er3+ doped CaAl4O7 phosphors

Here the green-emitting highly luminescent Er³⁺ doped, Er³⁺-Li⁺ co-doped, Er³⁺-Na⁺ co-doped CaAl₄O₇ is synthesized by Pechini method at 1000^°C. Photoluminescence (PL) of CaAl₄O₇: Er³⁺ studies have been compared with Li⁺ co-doped CaAl₄O₇: Er³⁺ and Na⁺ co-doped CaAl₄O₇: Er³⁺. Na⁺ co-doped CaAl₄O₇:Er³⁺ shows increases in luminescence intensity compared to Li⁺ co-doped CaAl₄O₇: Er³⁺ and Er³⁺ doped CaAl₄O_7. The results suggest that CaAl₄O₇:Er³⁺ phosphor can be used as efficient green-emitting phosphor in white LED. The resultant phosphor emits green color peaking at 549 nm upon 378 nm excitation. Powder X-ray diffraction (PXRD) and photoluminescence (PL) techniques have been studied to characterize the synthesized microparticles. Further, this phosphor has good thermal stability that implies its potential to act as green phosphor in white light-emitting diodes. The effect of activator (Er³⁺), Na⁺ co-doped CaAl₄O₇:Er³⁺, and Li⁺ co-doped CaAl₄O₇:Er³⁺ phosphors luminescence spectra as well as photoluminescence life time studies were studied in detail. The results show that as the concentration of Er³⁺ in CaAl₄O₇ increases, the symmetry around the Er³⁺ ion decreases due to the creation of lattice defects in the crystal. Addition of Na⁺ and Li⁺ ions in CaAl₄O₇: Er³⁺leads to a small distortion in the local symmetry of Er³⁺ ions, thereby significantly enhancing its luminescence property. Analysis of photoluminescence life time studies of the prepared samples shows a smaller concentration quenching of Er³⁺ luminescence in charge compensated Na⁺ and Li⁺ CaAl₄O₇ phosphor.

     

Green synthesis and luminescent properties of seven coordination K3ZrF7:Mn4+ red phosphor for warm WLEDs

Journal of Materials Science: Materials in Electronics - The seven-coordinated K3ZrF7:Mn4+ red phosphor was synthesized by green route. The structure, composition and morphology were characterized...     

Enhanced persistent luminescence of MgGa2O4:Cr3+ near-infrared phosphors by codoping Nb5+

Journal of Materials Science: Materials in Electronics - Near-infrared (NIR) long persistent phosphors have potential applications in medical imaging, anti-counterfeiting signs, and night vision...     

Synthesis and luminescence properties of Eu2+- and Mn2+-activated Mg21Ca4Na4(PO4)18 phosphors

Rare earth-doped phosphates have attracted much attention in recent years because of their interesting optical applications. However, few studies have reported on optical properties of fillowite-like compounds. Eu²⁺ and Mn²⁺ singly doped and Eu²⁺/Mn²⁺-codoped Mg₂₁Ca₄Na₄(PO₄)₁₈ phosphors were synthesized for the first time via combustion-assisted synthesis technique. The Eu²⁺-activated sample emits an intense blue light under 360 nm excitation, while the Eu²⁺/Mn² + -codoped Mg₂₁Ca₄Na₄(PO₄)₁₈ sample exhibits a broad blue emission band and a red emission band, resulting from Eu²⁺ and Mn²⁺, respectively. Energy transfer between Eu²⁺ and Mn²⁺ was discovered and the transfer efficiency was also estimated based on relative intensities of Eu²⁺ and Mn²⁺ emission. Thus, the relative strength of blue and red emission intensities could be tuned by varying the relative concentration of Eu²⁺ and Mn²⁺. Since the photoluminescence excitation spectra of the newly developed Mg₂₁Ca₄Na₄(PO₄)₁₈:Eu²⁺, Mn²⁺ phosphors exhibit a strong absorption in the range of 250–400 nm, they are promising for producing UV-LED-based white LEDs.     

Synthesis and luminescence of Dy3+-activated NaSrPO4 phosphors for novel white light generation

The Dy³⁺-doped NaSrPO₄ phosphor powders have been synthesized by solid state reaction. All samples were verified to be in a pure NaSrPO₄ phase by X-ray diffraction analysis for all the Dy³⁺ doping concentrations. The room temperature excitation spectra of NaSrPO₄:Dy³⁺ phosphors illustrated that they could easily be excited by UV–Visible light corresponding f ? f transitions of Dy³⁺. The photoluminescence spectra exhibit two main bands centered at 481 nm (blue) and 573 nm (yellow), which originate from the ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions of Dy³⁺, respectively. The two bands combined to form a white light with the chromaticity coordinates varying with the concentrations of Dy³⁺. The chromaticity coordinates were measured and mapped in the Commission International de L’Ecllairage 1931 diagram, indicating that they distributed around (0.30, 0.34) of the colorless point D65. The dependence of luminescence intensity onto Dy³⁺ concentration was investigated and the concentration quenching mechanism for NaSrPO₄:Dy³⁺ was discussed.     

Effect of Zr4+ and Si4+ substitution on the luminescence properties of CaMoO4:Eu3+ red phosphors

A series of intense red emitting phosphors, Ca_0.8?x Zr _x Mo_1?x Si _x O₄:0.2Eu³⁺ (x = 0.025, 0.05, 0.075, 0.1) that could be effectively excited in the UV region was prepared by conventional high temperature solid state reaction route. Structural, morphological and photoluminescence properties of the prepared samples were studied in detail. The incorporation of Zr⁴⁺ and Si⁴⁺ ions in CaMoO₄ lattice maintained the powellite crystal structure. Luminescence properties were optimized for 7.5 mol% of Zr⁴⁺ and Si⁴⁺ concentration. Emission intensities improved more than twice in comparison with CaMoO₄:Eu³⁺. Life times of the prepared samples improved and the quantum efficiency enhanced to ~39 %. The improvement in emission intensity and quantum efficiency is explained in terms of the local distortion around the Eu³⁺ ions resulting in improved absorption in the UV region. The CIE color co-ordinates of the red emission were in agreement with the values of the standard red phosphors providing potentiality to be used in phosphor converted (pc) white LEDs.     

White organic light-emitting devices utilizing a mixed color-conversion phosphor layer consisting of CaAl12O19:Mn and Zn2SiO4:Mn

White organic light-emitting devices (WOLEDs) were fabricated utilizing a mixed color-conversion layer consisting of CaAl12O19:Mn and Zn2SiO4:Mn phosphors. The ratio between the CaAl12O19:Mn and the Zn2SiO4:Mn phosphor determined the rate of the red and the green lights. The color rendering index was improved by using a mixed color-conversion phosphor layer.     

Morphology control and photoluminescence of BaMgAl10O17:Eu2+, Mn2+ phosphors prepared by flux method

The blue phosphor Ba_0.9 Mg_0.98Al₁₀O₁₇:0.1Eu²⁺, 0.02Mn²⁺ (BAM:Eu²⁺, Mn²⁺) was prepared by flux assisted solid-state reaction method. The effects of (NH₄)₂CO₃ and LiF on the morphology and luminescent properties were studied. The usually obtained BAM:Eu²⁺, Mn²⁺ particles had hexagonal shape. We found that the thickness of the particle was affected by the amount of LiF and spherical-like particles can be obtained. The significant change on morphology from plate-like to spherical-like shape led to a highly enhanced luminescence of BAM:Eu²⁺, Mn²⁺. The maximum luminance intensity of prepared samples was 108% in comparison with the commercial BAM:Eu²⁺, Mn²⁺ under UV excitation.     

化学共沉淀法合成小粒径BaAl12O19:Mn2+绿色荧光粉

使用化学共沉淀法合成出VUV激发的BaAl12O19：Mn^2＋绿色荧光粉。通过对共沉淀条件的控制,获得了Ba^2＋、Al^3＋、Mn^2＋离子的完全沉淀,且使其中的Al^3＋以结晶碳酸铝铵形式沉淀,从而避免了高温合成时容易出现的硬团聚现象;在共沉淀产物中加入了自行研制的促进剂,不仅使合成温度比传统高温固相法降低了约300～400℃,且有效地控制了BaAl12O19：Mn^2＋荧光粉的颗粒大小和形貌,制备出的荧光粉颗粒呈六角片状,粒径1～2μm,且分散性良好。在λex=147nm激发时,该荧光粉色坐标x=0．145,y=0．755。     

The effects of Mn2+ doping on the luminescence properties of 12CaO 7Al2O:Eu2+ nanocrystal phosphor

The long lasting blue phosphorescence (LLP) and photostimulated luminescence (PSL) after ultraviolet light irradiation at room temperature in 12CaO 7Al2O3:xEu2+, yMn2+ (x = 0, 0.001; y = 0, 0.01) prepared by the chemical co-precipitation method were observed. It was shown that novel oxide 12CaO 7Al2O3:Eu2+, Mn2+ (C12A7:Eu2+, Mn2+) with unique nanocage structure can store energy when irradiated with 365 nm photons. And photon energy can be subsequently released by exposed to 980 nm light. The codopant Mn2+ enhances the intensity of the persistent phosphorescence and PSL due to the existence of more shallow and new deeper electron traps in C12A7: Eu2+, Mn2+. A model for energy storing and recovering and the detailed mechanism of PSL are presented through comparing with the luminescence properties of the co-doped C12A7:Eu2+, Mn2+ and C12A7:Eu2+.     

Matrix-inducing synthesis and luminescence of microcrystalline red phosphors YVO4:Pb2+,Eu3+ derived from the in situ coprecipitation of hybrid precursors

Using rare-earth coordination polymers with o-hydroxylbenzoate as a precursor, composing with polyvinyl alcohol as a dispersing medium, a novel red-emitting material of YVO₄:xPb²⁺, yEu³⁺ (x=0, 1.0, 1.2, 1.5, 1.8, 2.0, and 5.0 mol %; y=5 mol %) was synthesized by an in situ coprecipitation process. Its microstructure and micromorphology have been analyzed by x-ray powder diffraction and scanning electronic microscopy, which indicates that there exist some novel cobblestone-like microcrystalline particles. With Pb²⁺ as a sensitizer, these materials all exhibit strong red emission near 618 nm due to the ⁵ D ₀ → ⁷ F ₂ transition of Eu³⁺ ions. At x=1.5, YVO₄:Pb²⁺, Eu³⁺ shows the strongest emission intensity, which indicates an efficient energy transfer from Pb²⁺ to Eu³⁺. The text was submitted by the authors in English.     

Synthesis and luminescence properties of Sr2SiO4: Eu3+, Dy3+ phosphors by the sol-gel method

The Sr2SiO4:Eu3+, Dy3+ phosphors for white light emitting diodes (LEDs) were synthesized by the sol-gel method. The microstructure and luminescent properties of the obtained Sr2SiO4:Eu3+, Dy3+ particles were well characterized. The results demonstrate that the Sr2SiO4:Eu3+, Dy3+ particles, which have spherical morphology, emitted an intensive white light emission under excitation at 386 nm. The phosphors show three emission peaks: the blue emission at 486 nm corresponding to the 4F(9/2)-6H(15/2) transition of Dy3+, the yellow emission at 575 nm corresponding to the 4F(9/2)-6H(13/2) transition of Dy3+, and the red emission at 615 nm corresponding to the 5D0-7F2 transition of Eu3+. At the same time, the effect of Eu3+ concentration on the emission intensities of Sr2SiO4:Eu3+, Dy3+ was investigated in detail. The phosphors used for white LEDs were obtained by combining near ultraviolet (NUV) light (386 nm) with Sr2SiO4:0.04Dy3+, 0.01Eu3+ phosphors with the characteristic of Commission Internationale de l'Eclairage (CIE) chromaticity coordinate (x, y) of (0.33, 0.34), and color temperature Tc of 5,603 K. In addition, the effect of the charge compensators (Li+, Na+, and K+ ions) on the photoluminescence (PL) emission intensities were studied.     

锰锌铁氧体磁流体中Zn2+的作用及其影响机理的研究

采用化学共沉淀法制备了Mn1-xZnxFe2O4磁流体,全面分析并探讨了Zn2+的作用及其影响机理.研究表明Zn2+的含量对于Mn1-xZnxFe2O4磁流体的磁性能具有至关重要的影响,当Zn2+的含量为0.22时,所制得磁流体的磁性能最好.X射线衍射分析结果表明磁性粒子由单一物相构成,其晶格常数为a=0.846nm,介于MnFe2O4与ZnFe2O4之间.Mn0.78Zn0.22Fe2O4磁流体在外加磁场作用下显示出超顺磁性,其比饱和磁化强度随着质量百分比浓度的增加而增大,最高可达32.17A*m2/kg.     

调控Al2O3晶型控制MgAl2O4:Mn4+荧光粉中Mn价态研究

Mn4+激活红光荧光粉是白光半导体发光二极管(wLEDs)领域当前研究热点之一.Mn4+离子2E→4A2跃迁在铝酸盐中的最短发光波长是在MgAl2O4中实现的651nm发光,由于其结构中含有形成四面体或八面体配位的两种阳离子格位(Mg2+/Al3+),易造成所掺杂锰元素存在多种价态(+2/+4/+3等).本研究通过改变...     

Effects of the mixing ratio of the CaAl12O19:mn and Zn2SiO4:mn color-conversion layer on the color tunable emissions of white organic light-emitting devices

The optical properties of white organic light-emitting devices (WOLEDs) fabricated utilizing a CaAl12O19:Mn and Zn2SiO4:Mn phosphor layer were investigated. X-ray diffraction patterns for CaAl12O19:Mn and Zn2SiO4:Mn phosphors showed that Mn ions in the CaAl12O19:Mn phosphors were completely substituted into Ca ions and that Mn ions in the Zn2SiO4:Mn phosphors were completely substituted into Zn ions. Field emission scanning electron microscopy images showed that the size of the CaAl12O19:Mn phosphor was approximately between 0.1 and 3 microm, and that the size of the Zn2SiO4:Mn phosphor was smaller than 7 microm. The color coordinates of the electroluminescence spectra for WOLEDs with phosphor thicknesses of 0.25 and 0.35 mm shifted to the white emission side because the generated blue light from the blue OLEDs combined with the red and green lights was converted by the CaAl12O19:Mn and the Zn2SiO4:Mn phosphor down-conversion layers.     

Negative thermal quenching of K3AlF6:Mn4+@GQDs phosphors caused by enhancement of the conversion of heat energy into light energy

In order to improve luminescent thermal stability, a series of new K₃AlF₆:0.02Mn⁴⁺@GQDs _{x mg/mol} phosphors (graphene quantum dots: GQDs) have been synthesized with a coating strategy. Enhancement of luminescent thermal stability and emission induced by coating of GQDs are observed, which high luminescent thermal stability is caused by negative thermal quenching (NTQ). The mechanism of the NTQ is discussed and suggested as: some of thermal energy is transformed into light energy. Finally, warm white light with high color rendering index (Ra) and low correlated color temperature (CCT) is obtained from prototype white light-emitting diodes (WLEDs) using the optimal coated sample.