The effect of charge compensation by means of Na+ ions on the luminescence behavior of Sm3+-doped CaAl4O7 phosphor

Results of structural and spectroscopic measurements of Sm³⁺ doped calcium aluminates: Ca_1?xSm_xAl₄O₇ and Ca_1?2xSm_xNa_xAl₄O₇ (x=0.0005, 0.002, 0.01, 0.02, 0.03, 0.05) obtained by the modified Pechini method are presented. All samples yield intense orange–red emission under violet excitation (404.5 nm). Narrow bands corresponding to characteristic f–f intraconfigurational transition of Sm³⁺ in excitation and emission spectra were observed. The influences of the concentration of Sm³⁺ as well as charge compensation by co-doping with Na⁺ ions on the luminescent properties of the phosphor were investigated. Detailed analysis of the emission spectra of Sm³⁺ doped and Sm³⁺,Na⁺ co-doped CaAl₄O₇ powders proved that activator ions substitute Ca²⁺ in the host. Co-doping with Na⁺ ions enhanced greatly the intensity of the luminescence. Concentration dependencies of the intensity of luminescence and its decay kinetics proved the emission quenching at higher dopant contents due to cross-relaxation processes between Sm³⁺ ions. Fitting of the ⁴G_5/2 state fluorescence decay to the Inokuti–Hirayama model indicated dipole–dipole interaction as the dominant mechanism of the cross-relaxation processes.     

Influence of colloidal-gold films on the luminescence of Eu(TTFA)3 in PMMA

The effects of colloidal-gold layers on the luminescent properties of thin films of Eu(TTFA)₃(TTFA=thenoyltrifluoroacetonate) in PMMA (PMMA=poly(methyl methacrylate)) were investigated. Layers of spherical gold nanoparticles (12 nm) were formed by self-assembly on the surface of amino-derivatized glass slides. Eu(TTFA)₃-PMMA films were then spin-coated either directly onto the Au metal surfaces or onto spacer layers covering the gold. The luminescence properties were characterized both as a function of the density of Au particles in the colloidal layer, and as a function of the distance between the Au layer and the luminescent film. The distance between the metal and luminescent layers was controlled using polyelectrolyte spacer layers deposited on the colloidal-gold films by a spin-assisted, layer-by-layer (SA-LBL) method. It was found that the colloidal gold layer has a net quenching effect on Eu(TTFA)₃ luminescence under all conditions considered in this study. The luminescence intensities and lifetimes decrease with increasing density of Au nanoparticles and with decreasing separation (d) between the luminescent film and the gold layer. The measured luminescence intensity drops more quickly with decreasing distance than one would predict based solely on lifetime data, if one assumes a constant radiative relaxation rate. Fits of the luminescence decay kinetics to a model for non-radiative energy-transfer from Eu(TTFA)₃ to the gold layer yields a 1/d² dependence, where d is the distance from the gold layer to the nearest face of the luminescent film. It is suggested that there is no reasonable physical interpretation of this result within the constraints of the model and, therefore, the interaction between the luminescent and gold layer cannot be explained solely in terms of non-radiative energy transfer.     

Eu(TTFA)3掺杂SiO2杂化胶体球的合成及特性

采用改进的碱催化法和种子法分别制得了稀土配合物Eu(TTFA)₃掺杂的SiO₂杂化胶体球,并用透射电子显微镜和荧光分光光度计对其显微形貌和荧光光谱特性进行了详细地研究.结果表明,两种方法都可以获得单分散性的、稀土配合物掺杂SiO₂杂化胶体球,且都具有Eu³⁺离子典型的荧光光谱特性.Eu(TTFA)₃掺杂入SiO₂胶体球中后,有机配体TTFA在短波长处的吸收明显增强了,最大的吸收峰位也向短波长方向移动大约20～30 nm,Eu³⁺离子5D0→7F2发射跃迁仍然具有良好的窄线发光特征,同时荧光峰值的形态和位置受SiO₂基体的影响发生轻微的变化.     

Synthesis,crystal structure,and luminescence properties of CaY2Ge3O10:Ln3+, Ln = Eu,Tb

The crystal structure and luminescence properties of CaY₂Ge₃O₁₀:Ln³⁺ (Ln = Eu, Tb) germanates synthesized via a conventional solid-state reaction and an ethylenediaminetetraacetic acid complexing process are studied. The CaY_{2 ? x} Ln _x Ge₃O₁₀ (Ln = Eu, Tb; x = 0–1.0, 2.0; Δx = 0.1) solid solutions have a monoclinic structure (space group P2₁/c, Z = 4), in which dopant ions occupy three nonequivalent noncentrosymmetric sites with different Ca²⁺/Ln³⁺ ratios. The effect of the synthesis methods, dopant concentrations, and excitation wavelengths on the luminescence properties of the compounds obtained is determined.     

Photophysics of RbCl co-doped with Eu2+ and Eu3+

Excitation and luminescence spectra of RbCl co-doped with divalent and trivalent europium ions are reported. Spectral dips appearing in the blue emission from Eu²⁺ are resulted from the radiative energy transfer from Eu²⁺ to Eu³⁺ and consequently induces the luminescence from Eu³⁺ that is responsible for the ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) transitions. The induced luminescence has been characterized as a function of temperature and a decay time. In addition, the polarized emission from RbCl doped with only Eu²⁺ is also reported.     

Photoluminescence studies on Eu and Ce-doped Li2SrSiO4

The luminescence of Li₂SrSiO₄: 0.01Eu, xCe (x=0.0025, 0.005, 0.0075, and 0.01) is studied as a potential ultraviolet light-emitting diode (UV-LED) phosphor that is capable of converting the ultraviolet emission of a UV-LED into white light with good luminosity. There are broad blue and yellow emissions peaked at 413 and 575 nm, respectively. The two emissions come from d-f transitions of Ce³⁺ and Eu²⁺, respectively. The emission intensity of Li₂SrSiO₄: 0.01Eu, xCe reaches its maximum at x=0.0075. The energy transfer from Ce³⁺ to Eu²⁺ is demonstrated to be the type of electric dipole-dipole interaction with considerable spectral overlap and nonradiative transition is calculated to dominate. The Commission International de I’Eclairage (CIE) chromaticity coordinates of Ce³⁺/Eu²⁺ substituted compounds is also discussed.     

Eu3+/Sm3+共掺聚合物PMMA中敏化效应的研究

研究了Eu3+/Sm3+共掺聚合物PMMA中Sm3+对Eu3+发光的敏化效应,实验采用改进的本体聚合法制备得到了Eu3+/Sm3+共掺聚合物PMMA,并对其荧光光谱和荧光寿命进行了分析.荧光光谱分析发现,Sm(TTFA)3的加入大大增强了Eu3+的特征发光,表明Sm3+对Eu3+的荧光有很强的敏化效应,文中对其敏化过程进行了探讨与分析,提出了两种可能的敏化机理.荧光寿命分析表明,在共掺情况下,掺杂浓度对荧光寿命没有明显的影响,寿命范围在300~400 μs之间.     

Temperature-dependence of the structural and afterglow luminance properties of polymer/SrAlxOy:Eu,Dy composites

Although aluminate phosphors have attracted great interest for applications in lamps, cathode ray tubes and plasma display panels, there still remain issues affecting operational parameters such as luminescence efficiency, stability against temperature, high color purity and perfect decay time. In addition, issues involving important aspects of the monoclinic↔hexagonal phase transition temperature still exist. In this work, SrAl_xO_y:Eu²⁺,Dy³⁺ phosphor powders were prepared by the sol–gel method. X-ray diffraction (XRD) has shown that both crystallinity and crystallite sizes increased as the temperature increased. Both SrAl₂O₄ and Sr₂Al₃O₆ phases were observed. Photoluminescence (PL) characterization shows temperature-dependence, which indicates emission at low and high annealing temperatures originating from Eu²⁺ and Eu³⁺ ions. Thermoluminescence glow and decay measurements provided useful insight on the influence of traps on luminescence behavior. Differential scanning calorimetry (DSC) and thermogravimetric studies (TGA) on composites of the phosphor in low density polyethylene (LDPE) demonstrated the varied influence of annealing temperature on some luminescence and thermal properties.     

Role of Al coordination in barium phosphate glasses on the emission features of Ho ion in the visible and IR spectral ranges

The glasses of the composition (39−x)BaO-xAl₂O₃-60P₂O₅:1.0Ho₂O₃ (in mol%) with x value ranging from 1.0 to 4.0 have been synthesized. The IR spectral studies of these glasses have indicated that there is a gradual transformation of Al³⁺ ions from tetrahedral to octahedral with increase in the concentration of Al₂O₃ up to 3.0 mol%. Optical absorption and fluorescence spectra (in the visible and NIR regions) of these glasses have been recorded at room temperature. The Judd-Ofelt theory could successfully be applied to characterize the absorption and luminescence spectra of Ho³⁺ ions in these glasses. From the luminescence spectra, various radiative properties like transition probability A, branching ratio β_r, the radiative lifetime τ_r and emission cross-section σ^E for various emission levels of these glasses have been evaluated. The radiative lifetime of the ⁵S₂→⁵I₈ (green emission) transition has also been measured. The variations observed in these parameters have been discussed in the light of varying co-ordinations (tetrahedral and octahedral positions) of Al³⁺ ions in the glass network. The influence of hydroxyl groups on the luminescence efficiency of the transition ⁵S₂→⁵I₈ has also been discussed. Finally the optimum concentration of Al₂O₃ for getting maximum luminescence output has also been identified and reported.     

Luminescence studies on SrMgAl10O17:Eu, Dy phosphor crystals

Using urea as fuel, SrMgAl₁₀O₁₇:Eu, Dy phosphor was prepared by a combustion method. Its luminescence properties under ultraviolet (UV) excitation were investigated. Pure SrMgAl₁₀O₁₇ phase was formed by urea-nitrate solution combustion synthesis at 550 °C. The results indicated that the emission spectra of SrMgAl₁₀O₁₇:Eu, Dy has one main peak at 460 nm and one shoulder peak near 516 nm, which are ascribed to two different types of luminescent Eu²⁺ centers existing in the SrMgAl₁₀O₁₇ matrix crystal. The blue luminescence emission of SrMgAl₁₀O₁₇:Eu phosphors was improved under UV excitation by codoping Dy³⁺ ions. The SrMgAl₁₀O₁₇:Eu phosphors showed green afterglow (λ=516 nm) when Dy³⁺ ions were doped. Dy³⁺ ions not only successfully play the role of sensitizer for energy transfer in the system, but also act as trap levels and capture the free holes in the spinel blocks.     

Synthesis and luminescent properties of hexagonal BaZnSiO4:Eu2+ phosphor

A green-emitting phosphor of hexagonal BaZnSiO₄:Eu²⁺ was prepared by a combustion-assisted synthesis method and an efficient green emission from ultraviolet to visible light was observed. The luminescence and crystallinity were investigated by using luminescence spectrometry and X-ray diffractometry. In the hexagonal structure of BaZnSiO₄:Eu²⁺ phosphor, Eu²⁺ ions occupy three different lattice sites by substitution for Ba²⁺ ions. Eu²⁺ ions on Ba (1) and Ba (2) sites gave emissions at about 505 nm while Eu²⁺ ions on Ba (3) sites showed an emission band at 403 nm. The excitation spectrum is a broad band extending from 260 to 465 nm, which matches the emission of ultraviolet light-emitting diodes. The critical quenching concentration of Eu²⁺ in BaZnSiO₄:Eu²⁺ phosphor is about 0.05 mol. The value of the critical transfer distance is calculated as 10.97 Å. The corresponding concentration quenching mechanism is verified to be the electric multipole–multipole interaction. The CIE coordinates of the optimized sample $\mathrm{Ba}_{0.95}\mathrm{ZnSiO}_{4}{:}\mathrm{Eu}_{0.05}^{2+}$ were calculated as (x,y)=(0.172,0.463).     

The enhancement of luminescence in Co-doped cubic Eu2O3 using Li and Al ions

The co-doping of Li⁺ and Al³⁺ ions drastically enhances the luminescence of cubic Eu₂O₃. The integrated emission intensity of ⁵D₀→⁷F_J bands (J=1-4) at 580-710 nm increases by a factor of about 6.7 in the co-doped Eu₂O₃ compared to the un-doped Eu₂O₃. In order to confirm that the co-doped ions were actually incorporated into the host lattice, the structural characteristics were studied using Raman spectroscopy, XPS, XRD, photoluminescence lifetime, and an SEM. These analyses consistently indicate a certain structural evolution in their results with an increase in the co-doping concentration. Variations in the crystal structure, the crystal morphology, and the intensity variation of the Raman modes at 465 and 483 cm⁻¹ are presented as the evidences showing the incorporation of the co-doped ions into the host. The luminescence enhancement is discussed in terms of concentration quenching, reduction of defect sites, and the modification of the local symmetry of the Eu³⁺ ions, especially in the inversion symmetry sites.     

Middle infrared luminescence of Tb in silver halide crystals and fibers

The optical absorption and the luminescence emission were investigated in AgCl_xBr_1−x crystals (0<x<1) doped with Tb³⁺ ions and in fibers extruded from these crystals. Strong luminescence emission in the middle infrared (MIR) in the spectral range 4.2-5.6 μm was observed for the first time in such crystals and fibers.¹ Various optical parameters were calculated for the Tb³⁺-doped crystals, using the Judd-Ofelt approximation. The measured and the calculated results have indicated that these doped crystals could be used for the development of solid-state lasers or fiber lasers operating in the middle infrared.     

Probing of surface Eu ions present in ZnO:Eu nanoparticles by covering ZnO:Eu core with Y2O3 shell: Luminescence study

Eu³⁺ doped ZnO nanoparticles are known to have significance extent of surface Eu³⁺ ions due to a large difference in ionic radii. Effect of such Eu³⁺ ions on the luminescence properties of ZnO:Eu nanoparticles has been understood from the luminescence studies of ZnO:Eu nanoparticles covered with Y₂O₃ shell. Based on the asymmetric ratio of luminescence and extent of energy transfer, it is established that when ZnO:Eu nanoparticles are covered with Y₂O₃ shell, a part of Eu³⁺ ions present with ZnO:Eu core migrate to Y₂O₃ shell and occupy Y³⁺ lattice positions.     

Middle-infrared luminescence of Nd ions in silver halide crystals

The optical absorption and the luminescence emission in the middle infrared (mid-IR) were investigated in AgCl_xBr_1−x crystals doped with Nd³⁺ ions. Strong luminescence emission, in the spectral range 4.5-5.8 μm, in mid-IR was observed for the first time in Nd³⁺-doped silver halide crystals. Various optical parameters were calculated for the Nd³⁺-doped crystals, using the Judd-Ofelt approximation. The measured results and the calculated parameters indicate that these doped crystals could be used for the development of mid-IR solid-state lasers or mid-IR fiber lasers.     

Magnetic and dielectric properties of alkaline earth Ca and Ba ions co-doped BiFeO3 nanoparticles

Ca²⁺ and Ba²⁺ ions co-doped BiFeO₃ nanoparticles, Bi_0.8Ca_0.2−xBa_xFeO₃ (x=0-0.20), were prepared by a sol-gel method. The phase structure, grain size, dielectric and magnetic properties of the prepared samples were investigated. The results showed that the lattice structure of the nanoparticles transformed from rhombohedral (x=0) to orthorhombic (x=0.07-0.19) and then to tetragonal (x=0.20) with x increased. The dielectric properties of the nanoparticles were affected by the properties of the substitutional ions as well as the crystalline structure of the samples. The magnetic properties of the nanoparticles were greatly improved and the T_N of the nanoparticles was obviously increased. All the Ca²⁺ and Ba²⁺ ions co-doped BiFeO₃ nanoparticles presented the high ratio of M_r/M from 0.527 to 0.571 and large coercivity from 4.335 to 5.163 KOe.     

Photoluminescence properties of Y0.75-xGdxAl0.10BO3:Eu3+0.10, 0.05R3+ (R= Sc, Bi) (0.00≤x≤0.45)

Y$_{0.75 - x}$Gd_xAl_0.10BO$₃:Eu$^{3+}_0.10, 0.05R³⁺ ($R$=Sc, Bi) ($0.00 ≤ x ≤ 0.45$) powder samples are prepared by solid-state reaction and their luminescence properties are investigated. With the replacement of Y³⁺$ ions by Sc³⁺$ (or Bi³⁺)$ and Gd³⁺$ ions in (Y,Al)BO$₃:Eu, the intensities of emission at 254 and 147~nm are remarkably improved, because Sc³⁺$ ions can absorb UV light and transfer the energy to Eu³⁺$ ions efficiently. Moreover, Gd³⁺$ and Bi$^{3 + }$ ions act as an intermediate ``bridge' between the sensitizer and the activator (Eu³⁺)$ in energy transfer to produce light in the (Y, Gd)BO$₃:Bi³⁺$, Eu³⁺$ system more effectively. After doping an appropriate concentration of Gd³⁺$ into Y$_{0.50}$Gd$_{0.25}$Al_0.10BO$₃:Eu³⁺_{0.01}$, Bi$^{3+}_{0.05}$, the emission intensity reaches its maximum, which is nearly 110{\%} compared with the red commercial phosphor (Y,Gd)BO$₃:Eu and better chromaticity coordinates (0.650, 0.350) are obtained.     

Synthesis and luminescence properties of Er3+-doped Lu3Ga5O12 nanocrystals

The concentration-dependent luminescence properties of sol–gel-derived nanocrystalline Lu_3(1?x)Er_3xGa₅O₁₂ powders (where x=0.01, 0.05 and 0.1) have been studied. Laser-excited luminescence spectra, emission decays and upconversion luminescence of Er³⁺-doped Lu₃Ga₅O₁₂ nanocrystalline samples have been measured. The decay curve of the (²H_11/2,⁴S_3/2) emission exhibits a non-exponential behavior presumably due to cross-relaxation process. Moreover, near-infrared to visible upconversion luminescence has been observed in the green region for 1.0 mol% Er³⁺ ions in Lu₃Ga₅O₁₂ nanocrystals upon 815 nm excitation. The power dependence of the anti-Stokes luminescence suggests that upconversion is probably achieved through the sequential absorption of two photons. To the best of our knowledge, this is the first report on the preparation and optical properties of Er³⁺-doped Lu₃Ga₅O₁₂ in the form of nanocrystalline powders.     

Crystal growth and optical properties of Cr3+, Er3+, RE3+: Gd3Ga5O12 (RE=Tm,Ho, Eu) for mid-IR laser applications

In this paper we report on the optical properties of triply Cr³⁺, Er³⁺, and RE³⁺ (RE=Tm, Ho, Eu) doped Gd₃Ga₅O₁₂ crystals that were grown by the Czochralski method. Optical absorption, near-infrared (NIR), and mid-infrared (mid-IR) fluorescence spectra were characterized for the fabricated crystals and corresponding luminescence decay measurements under 654 nm excitation were also carried out. Based on the analysis of energy transfer process between Er and RE (RE=Tm, Ho, Eu) ions, the energy transfer efficiency (ETE) values were evaluated, correspondingly. From the spectral data of all the studied crystals, it is observed that the co-doped Cr³⁺ ion highly increases the absorption pump power and the three kinds of co-doped RE³⁺ ions depopulate the Er:⁴I_13/2 energy level effectively. The spectral analysis shows that titled rare earth doped crystals are promising materials for ～3.0 μm mid-IR laser applications and among them Cr,Er,Eu:GGG is relatively more suitable due to its excellent optical properties compared with others.