Synthesis and luminescence properties of novel β-Zn3BPO7:Ln (Ln = Ce3+, Eu2+, Eu3+) phosphors

This work first reports the synthesis and luminescence properties of rare earth Ce³⁺, Eu²⁺, Eu³⁺ ions doped β-Zn₃BPO₇ phosphors [β-Zn₃BPO₇:Ln (Ln = Ce³⁺, Eu²⁺, Eu³⁺)]. The phosphors were synthesized by a solid-state reaction at high temperature, and their luminescence properties were investigated by measuring the photoluminescence excitation and emission spectra. The f–d transitions of Ce³⁺ and Eu²⁺ ions in the host lattice are assigned and corroborated, which lead to the broad emission band in ultraviolet (UV) and visible region for Ce³⁺ and Eu²⁺ ions under UV excitation, respectively. Typical reddish orange emission from Eu³⁺ in the host lattice was also observed. The spectroscopic characteristics including Stokes shift, crystal field depression, electron–vibrational interaction, and charge transfer band were investigated and compared with that in other borophosphate phosphors. β-Zn₃BPO₇:Eu²⁺ and β-Zn₃BPO₇:Eu³⁺ phosphors show potential application in solid state lighting region.     

Ca2SiO4:Ln (Ln = Ce3+, Eu2+, Sm3+) tricolor emission phosphors and their application for near-UV white light-emitting diode

Tricolor emission Ca₂SiO₄:Ln (Ln = Ce³⁺, Eu²⁺, Sm³⁺) phosphors were synthesized by the conventional solid-state reaction method, and their photoluminescence properties were investigated. Ce³⁺-, Eu²⁺-, or Sm³⁺-doped Ca₂SiO₄ phosphors showed typical blue, green, or red luminescence in the CIE1931 chromaticity diagram, respectively. In addition, the luminescence efficiency of the tricolor emission Ca₂SiO₄:Ln (Ln = Ce³⁺, Eu²⁺, Sm³⁺) phosphors was evaluated. A series of white light-emitting diode (LED) prototypes were fabricated by combining near-UV LED chip and the as-prepared tricolor emission phosphors with various ratios in weight. White LED prototypes with tunable correlated color temperature and color-rendering index values were realized by controlling the amount of phosphors. The presented results indicated the potential application of Ca₂SiO₄:Ln (Ln = Ce³⁺, Eu²⁺, Sm³⁺) phosphors in near-UV white LED.     

VUV–UV luminescence of Ce3+, Tb3+, Eu3+, and Dy3+ doped GdOCl

The vacuum ultraviolet spectroscopic properties of GdOCl:Re³⁺ (Re³⁺ = Ce³⁺, Tb³⁺, Eu³⁺, and Dy³⁺) are investigated in detail for the first time. The host absorption band is determined to be around 179 nm, and the f–d transition bands as well as the charge transfer bands are assigned. Upon 179 nm excitation, Re³⁺ (Re³⁺ = Ce³⁺, Tb³⁺, Eu³⁺, Dy³⁺) ions shown their characteristic emissions. Energy transfers from Gd³⁺ to Re³⁺ ion were observed. A broad band ranging from 350 to 400 nm corresponding to the d–f transition of Ce³⁺ is observed. Eu³⁺ has typical red emission with the strongest peak at 620 nm; Tb³⁺ shows characteristic transition of ⁵D_3,4 → ⁷F_j, and its spin-forbidden and spin-allowed f–d transitions in VUV region are calculated with Dorenbos’ equations, these calculated values agree well with the experimental results. Dy³⁺ presents yellow emission (⁴F_9/2 → ⁶H_13/2) with the strongest peak at 573 nm.     

Synthesis and luminescent properties of Tb3+ activated AWO4 based (A = Ca and Sr) efficient green emitting phosphors

Optically efficient terbium activated alkaline earth metal tungstate nano phosphors (AWO₄ [A = Ca, Sr]) with different doping concentrations have been prepared by mechanochemically assisted solid state metathesis reaction at room temperature for the first time. The prepared phosphors were characterized by the X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), Fourier transform Raman (FT-Raman) spectroscopy, photoluminescence and diffuse reflectance spectroscopy measurements. The XRD and Raman spectra results showed that the prepared powders present a scheelite-type tetragonal structure. FTIR spectra exhibited a high absorption band situated at around 850 cm^?1, which was ascribed to the W–O antisymmetric stretching vibrations into the [WO₄]^2? tetrahedron groups and the SEM images reveal that the particle sizes were in the range of 20–60 nm. The excitation and the emission spectra were measured to characterize the luminescent properties of the phosphors. The excitation spectrum exhibits a charge transfer broad band along with some sharp peaks from the typical 4f–4f transitions of Tb³⁺. Under excitation of UV light, these AWO₄:xTb³⁺ (A = Ca, Sr) phosphors showed a strong emission band centered at 545 nm (green) which corresponds to ⁵ D ₄ → ⁷ F ₅ transition of Tb³⁺. Analysis of the emission spectra with different Tb³⁺ concentrations revealed that the optimum dopant concentration for CaWO₄:xTb³⁺ and SrWO₄:xTb³⁺ phosphors are about 8 and 6 mol% of Tb³⁺. The green emission intensity of the solid state meta-thesis prepared CaWO₄:0.08Tb³⁺ and SrWO₄:0.06Tb³⁺ phosphors are 1.5 and 1.2 times greater than that of the commercial LaPO₄:Ce, Tb green phosphor. All properties show that AWO₄:Tb³⁺ (A = Ca, Sr) is a very appropriate green-emitting phosphor for fluorescent lamp applications.     

Preparation and luminescence properties investigation of Eu3+, Tb3+-doped LaNbO4:RE3+ (RE = Eu,Eu/Tb,Tb)

Journal of Materials Science: Materials in Electronics - In this work, doped and co-doped LaNbO4:RE3+ (RE?=?Eu, Eu/Tb, Tb) single crystals were prepared by a unique hydrothermal method...     

Facile synthesis of β-NaYF4:Ln3+ (Ln = Eu, Tb, Yb/Er, Yb/Tm) microcrystals with down- and up-conversion luminescence

β-NaYF₄:Ln³⁺ (Ln = Eu, Tb, Yb/Er, Yb/Tm) hexagonal microrods have been successfully synthesized through a facile molten salt method without any surfactant. X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, high-resolution transmission electron microscopy, and photoluminescence spectra were used to characterize the samples. It is found that at a preferred reaction temperature of 400 °C, the structure of β-NaYF₄ can gradually transform from microtubes to microrods as reaction time extends from 0.5 to 4 h. Furthermore, as the molar ratio of NaF:RE³⁺ (RE represents the total amount of Y³⁺ and the doped rare earth elements such as Eu³⁺, Tb³⁺, Yb³⁺/Er³⁺, or Yb³⁺/Tm³⁺) increased, the phase of sample transforms from YF₃ into NaYF₄. Under the excitation of 395 nm ultraviolet light, β-NaYF₄:5 %Eu³⁺ shows the emission lines of Eu³⁺ corresponding to ⁵D_0-3 → ⁷F _J (J = 1–4) transitions from 400 to 700 nm, resulting in red down-conversion (DC) light emission. When doped with 5 % Tb³⁺ ions, the strong DC fluorescence corresponding to ⁵D₄ → ⁷F _J (J = 6, 5, 4, 3) transitions with ⁵D₄ → ⁷F _J (green emission at 544 nm) being the most prominent group that has been observed. Moreover, upon 980 nm laser diode excitation, the Yb³⁺/Er³⁺- and Yb³⁺,Tm³⁺- co-doped β-NaYF₄ samples exhibit bright yellow and blue upconversion (UC) luminescence, respectively, by two- or three-photon UC process. The luminescence mechanisms for the doped lanthanide ions were thoroughly analyzed.     

Synthesis and luminescence properties of highly uniform SiO2@LaPO4:Eu3+ core–shell phosphors

SiO₂@LaPO₄:Eu³⁺ core–shell phosphors have been successfully synthesized by a one-step and economical wet-chemical route at low temperature. The as-obtained products were characterized by means of photoluminescence spectroscopy (PL), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS). The SEM, EDS and XPS analysis indicate that SiO₂@LaPO₄:Eu³⁺ core–shell phosphors can only be synthesized in a pH range of 8–11 and the possible mechanism has been proposed. The XRD results demonstrate that the structure of LaPO₄:Eu³⁺ layers is transferred into monoclinic phase from hexagonal phase after annealing at 800 °C for 2 h. The SiO₂@LaPO₄:Eu³⁺ phosphors show strong orange–red luminescence under ultraviolet excitation. The relative emission intensity of Eu³⁺ increases with increasing the annealing temperature and the number of coating cycles, and the optimum concentration for Eu³⁺ was determined to be 5 mol% of La³⁺ in SiO₂@LaPO₄ phosphors.     

Peculiarities in the electrical and magnetic properties of cobalt perovskites Ln1−xMxCoO3 (Ln3+: La3+, M2+: Ca2+, Sr2+, Ba2+; Ln3+: Nd3+, M2+: Sr2+)

We refer here to the electrical and magnetic properties of the Ln_1−xM_xCoO₃ systems (Ln³⁺: La³⁺, M²⁺: Ca²⁺, Sr²⁺, Ba²⁺; Ln³⁺: Nd³⁺, M²⁺: Sr²⁺), paying special attention to those ferromagnetic compounds that display M–I transitions as temperature rises: La_1−xM_xCoO₃ (M²⁺: Ca²⁺, Sr²⁺, Ba²⁺) in the compositional interval x=0.2–0.3, and Nd_1−xSr_xCoO₃, with x=0.40. The magneto-transport properties of such materials are peculiar and interesting: they show diodic behavior and large relaxation effects — these latter being specially important in the Nd compound — they display magnetoresistive effects specially at the M–I transition temperatures, and they age with time. All these results are discussed on the basis of the inhomogeneous electronic structure of these doped cobalt perovskites and taking into account the influence of the lanthanide ion on their magnetic and electrical properties.     

Synthesis and Upconversion Emission of β-Ca2SiO4: (Er3+, Yb3+)

The β-Ca₂SiO₄: (Er³⁺, Yb³⁺) powders were synthesized by the simple solid-state process. The obtained samples were given characterizations of X-ray diffraction, Fourier-transform infrared, transmission electron microscopy, and luminescence. The samples have monoclinic parawollastonite phase and irregular morphology. Under the excitation at 980 nm, the obtained β-Ca₂SiO₄: (Er³⁺, Yb³⁺) samples show the intense upconversion (UC) emission. The dosage of Yb³⁺ has obvious influence on the emission intensities of β-Ca₂SiO₄: (Er³⁺, Yb³⁺) samples. Also, the emission intensity increases gradually with the increasing pump power from 350 to 600 mW. On the basis of luminescent properties of samples, we can conclude that the UC emission originates from the biphotonic process.     

Color-tunable luminescence by energy transfer mechanism in RE (RE = Eu2+, Tb3+)–doped Na2SrPO4F phosphors

Journal of Materials Science: Materials in Electronics - In the current research work, Eu2+, Tb3+ singly doped and co-doped Na2SrPO4F phosphors have been synthesized by solid-state reaction method...     

Synthesis,structural studies,electrical conductivity and optical properties of new Sb2−xLnxTe3 (Ln: Lu3+, Er3+ and Ho3+) nanomaterials

Ln-doped Sb₂Te₃ (Ln: Lu³⁺, Er³⁺, Ho³⁺) nanomaterials were synthesised by a co-reduction method in hydrothermal condition. Powder X-ray diffraction (XRD) patterns indicate that the Ln_xSb_2?xTe₃ crystals (Ln = Lu³⁺, x = 0.00–0.06; Er³⁺ and Ho³⁺ x = 0.00–0.04) are isostructural with Sb₂Te₃. The cell parameter a decreases for Ln_xSb_2?xTe₃ compounds upon increasing the dopant content (x), while c increases. Scanning electron microscopy and transmission electron microscopy images show that doping of Lu³⁺ and Ho³⁺ ions in the lattice of Sb₂Te₃ results in spherical nanoparticles while that in Er³⁺ leads to hexagonal nanoplates, respectively. The electrical conductivity of Ln-doped Sb₂Te₃ is higher than that of pure Sb₂Te₃ and increases with temperature. By increasing the concentration of Ln³⁺ ions, the absorption spectrum of Sb₂Te₃ shows red shifts and some intensity changes. In addition to the characteristic red emission peaks of Sb₂Te₃, emission spectra of doped materials show other emission bands originating from f–f transitions of the Ho³⁺ ions.     

Sol–gel synthesis of long-lasting phosphors CdSiO3: Mn2+, RE3+ (RE = Tb,Eu, Nd) and luminescence mechanism research

Mn²⁺ and RE³⁺ (RE = Tb, Eu, Nd) co-doped CdSiO₃ orange phosphors were prepared at 1050 °C by a sol–gel method. The phase and crystallinity of the synthesized materials were investigated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The luminescence characteristics were analyzed using photoluminescence (PL) spectra, afterglow decay curves, long-lasting phosphorescence spectra, and thermoluminescence (TL) spectra. Due to the difference in co-doped rare earth ionic radii, it varied greatly in trap density and trap depth caused by the different defects deriving from RE³⁺ ions co-doping into the CdSiO₃: Mn²⁺ host. The afterglow intensity and time for these samples increased as follows: CdSiO₃: Mn²⁺0.2%, Nd³⁺0.8% < CdSiO₃: Mn²⁺0.4%, Tb³⁺0.8% < CdSiO₃: Mn²⁺0.4%, Eu³⁺0.3%. CdSiO₃: Mn²⁺0.4%, Eu³⁺0.3% had the best afterglow properties, which could be due to the proper traps formed by Eu³⁺ ions co-doping into the host. The role of RE³⁺ co-doped into the CdSiO₃: Mn²⁺ matrix and the possible long-lasting phosphorescence process was also discussed in this paper.     

Ln(Ln=Gd3+,Cu+,Sm3+,Dy3+)助激活的Ca8Mg(SiO4)4Cl2:Eu2+荧光粉的光谱特性和Eu2+的格位计算

采用高温固相法合成了掺杂Ln(Ln=Gd3+,Cu+,Sm3+,Dy3+)作助激活离子的氯硅酸镁钙荧光粉.通过X射线衍射(XRD)对Ca8Mg(SiO4)4Cl2:Eu2+,Ln进行了表征.结果表明Ln的共掺杂并没有影响基质晶体的面心立方结构.所合成的荧光粉发射峰值位于507nm的绿光区.激发光谱在330~430nm之间均有较强吸收,与紫光InGaN芯片(395nm)相匹配.掺杂Ln作助激活荆增强了荧光粉的发光强度.借助Uitert经验公式计算出Eu2+在Ca8Mg(SiO4)4Cl2基质中占据八配位Ca(Ⅱ)格位.