Fluorescence properties of divalent and trivalent europium ions in CdWO4 single crystals grown by the Bridgman method

Optical absorption,excitation,and fluorescence were investigated in Eu ion-doped CdWO4 single crystal grown by a modified Bridgman method.The results indicate that Eu2+ and Eu3+ ions coexist in CdWO4 crystal and an energy transfer occurs between these Eu2+ and Eu3+ ions.When the crystal is excited by 266-nm light,the energy corresponding to the 4f65d to 8S7/2 transition of Eu2+ ions results in the excitation of the Eu3+ ions to the 5DJ level.The effect on fluorescence of annealing in oxygen at various temperatures was investigated.The excitation intensity of Eu2+ ions at 266 nm decreases as annealing temperature increases from 300 K to 1073 K,but it remains at a certain equilibrium level when the annealing temperature is further increased.     

光谱探针法确定Eu3+:ThO2的格位对称性及选择激发下样品的光致发光研究

测量和分析了不同温度下Eu³⁺:ThO₂的激发光谱、发射光谱和荧光 衰减曲线.Eu³⁺:ThO₂晶体是用熔融法生长的.通过12K下格位选择激 发下的发射光谱测量,利用晶场理论,确定了Eu³⁺在ThO₂占据Oh和C_3v两种格位.列表给出了两种格位Eu³⁺离子的晶场能 级和室温及12K下的荧光寿命.讨论了温度对能     

掺Bi钨酸镉单晶体发光特性的研究

用坩埚下降法(Bridgman)生长出了Bi离子掺杂的CdWO₄单晶.测定了晶体不同部位的吸收光谱、发射光谱和X射线电子能谱(XPS).Bi离子的掺入引起CdWO₄晶体的吸收边从345 nm红移到399 nm.在311 nm, 373 nm,808 nm和980 nm光的激发下,分别观测到中心波长为470 nm,528 nm,1078 nm和较弱的1504 nm四个不同发射带.Bi:CdWO₄单晶的XPS谱分别与Bi₂ 关键词： Bi离子 荧光光谱 X射线电子能谱 4单晶')" href="#">CdWO₄单晶     

Optical spectroscopy of Mn2+ ions in CaCl2 single crystals

Abstract

In the present investigation the excitation and fluorescence spectra and lifetimes of Mn²⁺ ions in calcium chloride, for various manganese concentrations and sample temperatures have been studied for the first time. The fluorescence spectrum consists of an asymmetric broad band, which upon lowering the sample temperature, shifts its maximum from 580 nm at 300 K to 596 nm at 11 K. This luminescence band was associated with the ⁴T_lg(⁴G)→⁶A_lg(⁶S) spin-forbidden transition in the manganese ions occupying Ca-sites in the lattice of CaCl₂. The excitation spectrum of the Mn²⁺ fluorescence revealed the features of manganese ions in octahedral coordination and consisted of nine excitation peaks which were associated with Mn²⁺-crystal-field-sensitive transitions. A crystal field analysis of the wavelength positions of these transitions by means of the model developed by Curie et al. allowed us to determine the magnitude of the cubic field splitting 10Dq, the reduced Racah parameter B', the Koide-Pryce covalency parameter ε and the spin transfer coefficients f _[sgrave] and f _σ. From the measurement of the temperature dependence of the Mn²⁺ fluorescence lifetime, we have also obtained information about the different mechanisms which are involved in the relaxation of excited Mn²⁺ ions in this host crystal in the temperature range (11–300 K).     

Photoluminescence characteristics and energy transfer between Bi3+ and Eu3+ in Gd2O3: Eu3+, Bi3+ nanophosphors

Bi³⁺ and Eu³⁺ codoped cubic Gd₂O₃ nanocrystals were prepared by the Pechini sol-gel method. Their photoluminescent properties were investigated under ultraviolet light excitation. The introduction of Bi³⁺ ions broadened the excitation band of Eu³⁺ emission, of which a new strong band occurred ranging from 320 to 380 nm due to the 6s²→6s6p transition of Bi³⁺ ions, implying a very efficient energy transfer from Bi³⁺ ions to Eu³⁺ ions. Upon 325 and 355 nm light excitation, the luminescent intensity of Eu³⁺ ions was remarkably improved by the incorporation of Bi³⁺ ions. But a significant quenching of Eu³⁺ emission was observed under 266 nm light excitation when Bi³⁺ was codoped. The possible energy transfer processes between Bi³⁺ and Eu³⁺ were discussed. The decay curves of Eu³⁺ emission under the excitation of 266 nm pulsed laser were measured and gave further evidence for our discussion.     

Spherical Zn2SiO4:Eu@SiO2 phosphor particles in core-shell structure: Synthesis and characterization

Spherical SiO₂ particles have been coated with Zn₂SiO₄:Eu³⁺ phosphor layers by a Pechini sol-gel process. The microstructure and luminescent properties of the obtained Zn₂SiO₄:Eu³⁺@SiO₂ particles were well characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, and lifetime. The results demonstrate that the Zn₂SiO₄:Eu³⁺@SiO₂ particles, which have regular and uniform spherical morphology, emitted an intensive red light emission at 613 nm under excitation at 395 nm. Besides, the effects of the Eu³⁺ concentration, annealing temperature and charge compensators of Li⁺ ions on the PL emission intensities were investigated in detail.     

The charge states’ conversion of the activator ions in CaF2:Eu nanophosphors

According to stationary X-ray-excited luminescence spectra and thermally stimulated luminescence spectra of CaF₂:Eu nanophosphors, it was found that Eu³⁺?→?Eu²⁺ conversion can occur during thermal annealing of fine-grained (d?=?25?nm) nanoparticles in the 200–800°C range, which is accompanied by an increase in their size within 40–189?nm. An important role of the exciton mechanism of Eu²⁺ luminescence excitation was revealed according to the temperature dependence of X-ray-excited luminescence spectra of CaF₂:Eu nanoparticles of 114?nm size. The maximum of the X-ray-excited luminescence light output of CaF₂:Eu nanophosphors in the Eu²⁺ ions’ emission band was traced out at 400–500°C annealing temperature and at the size of nanoparticles of 114–180?nm. The subsequent growth of the annealing temperatures, particularly in the 800–1000°C range, causes the reduction of X-ray-excited luminescence light output because of the increment of lattice defects’ concentration due to a sharp increase in the size of nanoparticles and their agglomeration.     

Charge states of the activator and size effects in BaF2: Eu nanophosphors

ABSTRACT

According to the spectra of stationary X-ray excited luminescence (XEL) of BaF₂: Eu nanophosphors at 80 and 294 K, it was revealed that the thermal annealing of fine-grained nanoparticles (d?=?35?nm) in the range of 400–1000°C, which is accompanied by an increase of their sizes in the range of 58–120?nm, does not result in effective changes of the charge state of Eu^{3 +} → Eu^{2 +} activator, in contrast to CaF₂: Eu nanoparticles. The maximum light output of X-ray excited luminescence of BaF₂: Eu nanophosphors in the 590?nm emission band of Eu³⁺ ion was observed at an annealing temperature of 600°C with the average size of nanoparticles 67?nm. The subsequent growth of annealing temperatures, especially in the range of 800–1000°C, causes decrease in the light output of X-ray excited luminescence due to the increase of defect concentration in the lattice as a result of sharp increase of nanoparticle sizes and their agglomeration. In BaF₂: Eu nanoparticles of 58?nm size, according to the thermostimulated luminescence (TSL) spectrum, transformation of Eu³⁺ → Eu²⁺ under the influence of long-time X-ray irradiation was revealed for the peak of 151?K. Thus, X-ray excited luminescence spectra of BaF₂: Eu nanophosphors are formed predominantly due to the emission of Eu³⁺ ions, while emission of Eu²⁺ ions is observed in the TSL spectra.     

A study of the luminescence properties of Eu -doped borate crystal and glass

Eu³⁺-doped La₂O₃-3B₂O₃ crystal and glass were prepared by solid state reaction under different calcination temperature. The emission spectrum, phonon sideband (PSB), charge transfer band (C.T.B.) and lifetime of the Eu³⁺ ion in the two materials, with the same composition but with different phase, were investigated. With excitation at 394 nm light, the glass presented intense 618 nm red luminescence; however, the crystal gave 696 nm red luminescence. This difference is ascribed to the discrepancy of the local structure around the Eu³⁺ ion in the crystal and glass. To clarify the discrepancy, the coordination of Eu³⁺ in the borate glass and crystal was investigated. The results show that Eu³⁺ ions formed a complex Eu³⁺-O²⁻-B³⁺ bond in glass; however, in the crystal, it formed a complex Eu³⁺-O²⁻-La³⁺ bond. The lifetime of Eu³⁺ ions in the crystal and the glass is 3.08 ms and 1.98 ms, respectively. This indicates that the discrepancy in the local structure around the Eu³⁺ ions between the crystal and the glass leads to different fluorescence properties.     

Synthesis and Optical Properties of Eu3+ Ion Doped Nanocrystalline Hydroxyapatites

The Ca₁₀(PO₄)₆(OH)₂ hydroxyapatite (HA) nanopowders doped with Eu³⁺ ions were prepared using a wet synthesis method. Their structure and morphology were investigated. The XRD analysis has proven a single-phase of HA nanocrystallites. The average sizes of HA nanocrystallites calcinated at 400°C and 700°C were determined to be about 20 nm and 30 nm, respectively. The emission and excitation spectra as well as the fluorescence decay rates of Eu³⁺ ion doped HA nanocrystallites were measured. Particular attention was given to the spectroscopic properties of Eu³⁺ ions as a luminescent probe of nanocrystalline HA structure as a result of varying annealing temperature and dopant concentration. The Judd-Ofelt analysis of f-f transitions of Eu³⁺:HA nanocrystallites was performed. The effect of calcination temperatures on grain sizes and luminescence properties is noted and discussed.     

Effect of annealing temperature on luminescence of Eu ions doped nanocrystal zirconia

Effect of annealing temperature on luminescence of Eu³⁺ ions was studied in nanocrystal zirconia prepared by co-precipitation. The XRDs reveal with annealing temperature increasing the tetragonal crystal phase of the samples is stable. The emission spectra show the strong emission at 595 and 604 nm at 394 nm excitation. Under continuous UV (394 nm) irradiation the 604 nm emission intensity changes of the samples show as a function of irradiation time. In addition, the charge-transfer states of the samples are affected by the annealing temperature. These are associated with the defects at/in the surface of the nanocrystalline ZrO₂ with Eu³⁺ ions.     

White light generation through the zinc metaphosphate glass activated by Ce, Tb and Mn ions

The photoluminescence of Ce³⁺, Tb³⁺ and Mn²⁺ ions was investigated in the Zn(PO₃)₂ glass. The blue and green emissions of Tb³⁺ ions and the red emission of Mn²⁺ ions are enhanced upon UV excitation through a non-radiative energy transfer from Ce³⁺ to Tb³⁺ and Mn²⁺ ions. The efficiency of this transfer was estimated in at least 62%. It is demonstrated that this glass activated with three ions (Ce³⁺, Tb³⁺ and Mn²⁺) can generate white light emission (x=0.420 and y=0.423 chromaticity coordinates and 3440 K colour temperature) under excitation at 254 nm, i.e., using an AlGaN-based LED as excitation source.     

SBN晶体中Eu3+激发态的能量传递

通过选择激发SBN晶体中处于不同晶场位的Eu³⁺离子,得到⁵D₀→⁷F₁的时间分辨荧光光谱,确定了不等价晶场位的离子间的能量转移速率。荧光峰随激发波数的变化表明局部晶场的连续畸变。 关键词：     

Luminescent spectroscopy and structure of centers of the impurity Eu ions in lead tungstate crystals

Spectral-luminescent properties of the lead tungstate crystals doped with the Eu³⁺ ions were investigated in a wide temperature range at different excitation and registration wavelengths. The spectra consist of both weak wide nonstructural bands of the matrix emission and narrow spectral lines caused by inner f-f electron transitions in the impurity Eu³⁺ ions. The analysis and interpretation of spectral lines observed in excitation and luminescence spectra have shown formation of at least two different types of luminescent centers on the basis of the Eu³⁺ ions in the PbWO₄ crystals. These two types of centers are considered to be caused by arrangement of the impurity Eu³⁺ ions in Pb sites as well as in W sites of host matrix. For both types of centers values of S² scalar crystal field strength, and crystal field parameters were estimated and local site symmetries were found.     

Luminescence of CaGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>:Eu crystals

We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa₂Se₄:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm is due to intracenter transitions 4f⁶ 5d–4f⁷ (⁸S_7/2) of the Eu²⁺ ions. From the temperature dependence of the intensity (log I–10³/T), we determined the activation energy (E _a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths: 0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu²⁺ ions in the CaGa₂Se₄ crystal found from the luminescence decay kinetics is 3.8 μsec. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009.     

Electron paramagnetic resonance and luminescence of chromium in calcium germanate crystals

The luminescence of Ca₂GeO₄: Cr⁴⁺ single crystals at wavelengths in the range of 1.3 μm upon excitation with a 1-μ m semiconductor laser is investigated in the temperature range up to 573 K. At T<110 K, the Ca₂GeO₄: Cr⁴⁺ crystals are characterized by the electron paramagnetic resonance, which is attributed to the Cr⁴⁺ ions substituted for Ge⁴⁺ ions. The components of the g tensor and its principal axes are determined. It is revealed that the Cr⁴⁺ impurity centers in calcium germanate affect the crystal symmetry to a lesser degree compared to Cr⁴⁺ ions in forsterite. The observed deviation of the temperature dependence of the electron paramagnetic resonance from the Curie law is explained by the transition to the excited state with a low activation energy, as is the case in impurity 3d ions in diamond-like semiconductors. The inference is made that the giant effective degeneracy multiplicity of the excited state is associated with the initiation of soft phonon modes in the crystal upon excitation of the defect.     

The luminescence properties of Eu2+ doped Na2CaMg(PO4)2 phosphor

The blue-emitting phosphors of Eu²⁺-doped Na₂CaMg(PO₄)₂ were prepared by high-temperature solid-state reaction. The crystal phase formation was confirmed by X-ray powder diffraction measurement. The luminescence properties were investigated by photoluminescence excitation and emission spectra. The phosphor exhibited the blue luminescence due to the 4f⁶5d¹→4f⁷ transition of Eu²⁺ ions under the excitation of near UV light. The influence of temperature on the luminescence intensities and decay lifetimes of Eu²⁺ was investigated. An unusual increase of the decay lifetimes of the 4f⁶5d emission of Eu²⁺ ion is observed in Na₂CaMg(PO₄)₂ from 10 K to room temperature. The thermal stability of the luminescence of Eu²⁺-doped Na₂CaMg(PO₄)₂ was discussed.     

Europium luminescence in fluorite upon high-energy excitation

The reflection and luminescence excitation spectra of CaF₂ crystals containing europium ions in divalent (Eu²⁺) and trivalent (Eu³⁺) states were measured in the range from 4 to 16 eV. It was established that, in CaF₂ : Eu³⁺ crystals, luminescence of Eu³⁺ ions (the f-f transitions) is effectively excited both in the charge-transfer band (at ～8 eV) and in the region of the 4f–5d transitions (at ～10 eV) but is virtually not excited in the fundamental region of the crystal (at an energy higher than 10.5 eV). Luminescence of Eu²⁺ ions (the 427-nm band) in CaF₂ : Eu³⁺ is effectively excited in the fundamental region of the crystal; i.e., luminescence of divalent europium ions occurs through the trapping mechanism. Emission of Eu²⁺ ions in CaF₂ : Eu²⁺ crystals is characterized by the excitation band at an energy of 5.6 eV (the 4f → 5d,t _2g transitions), as well as by the exciton and interband luminescence excitations. The results obtained and data available in the literature are used to construct the energy level diagram with the basic electron transitions in the CaF₂ : Eu crystals.     

退火温度对ZrO2纳米材料中Eu3+离子发光的影响

研究了退火温度对ZrO₂纳米材料中Eu³⁺离子发光性质的影响. 材料的结构、晶粒尺寸和形状以及晶格的排列分别由XRD，TEM表征. 结果表明：用共沉淀法制备的ZrO₂纳米材料具有不随退火温度变化、稳定的四方结构；材料的晶粒尺寸随退火温度的提高而增大；晶格的排列由无序逐渐变为有序；发射光谱表明其主要发射在595 nm和604 nm处；在394 nm的紫外光辐照下得到了不同样品的604 nm荧光发射强度的变化不同. 这种现象与样品中O^2-离子含量和样品表面的表面缺陷有关；另外，电荷迁移带随退火温度的变化而变化.     

Photoluminescence of Eu in SrGa2S4

A photoluminescence (PL) study of the green-emitting SrGa₂S₄:Eu²⁺ phosphor is reported. Diffuse reflectance, excitation, and emission spectra were examined with the aim to enlarge the fundamental knowledge about the emission of the Eu²⁺ ion in this lattice. The thermal dependence of the radiative properties was investigated. In particular, the Stokes shift, the crystal field splitting and the activation energy of the thermal quenching were determined. By combining these results with the information presented in literature, we discussed the location of the Eu²⁺ levels relative to the valence and conduction bands of SrGa₂S₄.