Synthesis and the luminescent properties of europium-activated Ca2SnO4 phosphors

The synthesis and photoluminescent (PL) properties of calcium stannate crystals doped with europium grown by mechanically activated in a high energy vibro-mill have been investigated. The characteristics of Ca₂SnO₄:Eu³⁺ phosphors were found to depend on the amounts of europium ions. The XRD profiles revealed that the system, (Ca_1−xEu_x)₂SnO₄, could form stable solid solutions in the composition range of x = 0–7% after being calcined at 1200 °C. The calcined powders emit bright red luminescence centered at 618 nm due to ⁵D₀ → ⁷F₂ electric dipole transition. Both XRD data and the emission ratio of (⁵D₀ → ⁷F₂)/(⁵D₀ → ⁷F₁) reveal that the site symmetry of Eu³⁺ ions decreases with increasing doping concentration. The maximum PL intensity has been obtained for 7 mol% concentration of Eu³⁺ in Ca₂SnO₄.     

Temperature dependent luminescence in (Eu, Dy) doped tellurite glass

This short paper reports both the photoluminescence and the lifetime measurements of a prominent emission transition (⁵D₀→⁷F₂) of Eu³⁺ both in the presence and absence of the codopant rare earth ion (Dy³⁺) in an optical glass of the composition (79−x)TeO₂+6AlF₃+15LiF+xLn₂O₃ as a function of temperature down to 10 K.     

YVO4∶Eu3+,Bi3+红色荧光粉的水热合成及其荧光性能

以Y₂O₃、Eu₂O₃、Bi(NO₃)₃·H₂O、浓HNO₃、偏钒酸铵、氨水、无水乙醇和一缩二乙二醇为原料,采用聚乙烯吡咯烷酮(PVP)辅助水热法合成YVO₄: Eu³⁺, Bi³⁺纳米颗粒。使用X射线衍射(XRD)、扫描电镜(SEM)、红外光谱(IR)和荧光光谱(FL)等手段对产品进行了表征和分析。结果表明：合成的样品为YVO₄: Eu³⁺, Bi³⁺纳米颗粒,均具有四方晶相结构,其微结构随反应溶液的的pH值变化。YVO₄: Eu³⁺, Bi³⁺纳米颗粒在619 nm处有较强的红光发射(电偶极跃迁⁵D₀→⁷F₂),在594 nm有较弱的橙光发射(磁偶极跃迁⁵D₀→⁷F₁)。随着Eu/Bi比值的增大材料的荧光先增强后减弱,在Eu/Bi比值为5时样品的红光发射最强。溶液的pH值影响YVO₄: Eu³⁺, Bi³⁺纳米晶的发光强度,其中pH值为10时的样品其红光发射最强。并探讨了YVO₄: Eu³⁺, Bi³⁺纳米晶的发光机理。     

Eu3+掺杂Y2O3单分散红色荧光球形颗粒的尺寸可控合成与荧光性能

结合籽晶法和添加矿化剂硝酸铵, 通过均相沉淀合成和后续煅烧实现了(Y, Eu)₂O₃单分散球形颗粒(直径范围110~550 nm)的可控合成。通过XRD、FE-SEM、TEM和PLE/PL分析等手段对产物进行了系统表征。发现采用籽晶法和添加矿化剂硝酸铵可以促进球形颗粒长大。碱式碳酸盐前驱体经600℃煅烧分解为立方晶(Y, Eu)₂O₃, 且经1000℃煅烧后(Y, Eu)₂O₃依然继承球形形貌特征。所得多晶(Y, Eu)₂O₃球形荧光颗粒在242 nm激发下于615 nm处呈现最强红色荧光发射(Eu³⁺的⁵D₀→⁷F₂跃迁)。荧光粉的荧光性能呈现明显的尺寸依存性。增大球形颗粒尺寸减小了荧光寿命(1.15~1.57 ms)和荧光不对称因子[I(⁵D₀→⁷F₂)/I(⁵D₀→⁷F₁)], 但增强了荧光发射强度。     

柔性Eu3+掺杂SiO2纳米纤维薄膜的制备及其发光性能

采用溶胶-凝胶法结合静电纺丝技术制备了柔性Eu³⁺掺杂SiO₂纤维薄膜, 采用SEM、XRD、FT-IR、TG和PL等测试方法对材料进行表征。Eu³⁺掺杂SiO₂纤维薄膜在热处理后纤维直径变小, 纤维表面平滑无粘连。通过控制升温速度, 纤维薄膜经热处理后仍具有较高的力学强度, 750℃热处理后其拉伸强度可达4.31 MPa, 经过多次弯曲仍能保持原样。在392.6 nm光源激发下, Eu³⁺掺杂SiO₂纤维薄膜在570~670 nm附近呈现出来自于⁵D₀→⁷F_J的发射峰。当Eu³⁺掺杂浓度为8mol%时, 经过750℃热处理后Eu³⁺掺杂SiO₂纤维薄膜的发光强度达到最大值。     

Infrared absorption and Zeeman effect in Nd doped YVO4

Low temperature infrared transmission studies of Nd³⁺ doped YVO₄ were performed, under a magnetic field B c, in the 1800–8000 cm⁻¹ range of the ⁴I_9/2→⁴I_11/2, ⁴I_13/2, and ⁴I_15/2 Nd³⁺ crystal-field transitions. Good agreement is obtained between the experimental and calculated g-factors. Frequencies of the satellites in the ⁴I_9/2→⁴F_3/2 transitions of the Nd³⁺ isolated ion confirm the presence of ferromagnetic interactions between pairs of coupled Nd³⁺ ions that lift the Kramers doublet degeneracies of their ground state and excited multiplets.     

Optical properties of rare earth ion (Nd, Er and Tb)-doped alumina films prepared by the sol–gel method

Rare earth ion (Nd³⁺, Er³⁺ and Tb³⁺)-doped alumina films were prepared by the sol–gel method using aqueous alumina sol. The effects of dopant concentration and treatment temperature on the optical properties, absorption and emission were examined for the doped films. Alumina films prepared by this method gave a high dopant concentration (0–15 mol% per alumina). Significant concentration quenching did not occur in this concentration range. The emissions from ⁵D₃ and ⁵D₄ of Tb³⁺-doped film reflected sensitively a matrix environment around Tb³⁺ ions. Er³⁺- and Nd³⁺-doped alumina films resonantly excited by cw Ti–sapphire laser (800 nm) showed upconversion emission at room temperature. The former gave 548 nm (⁴S_3/2→⁴I_15/2) and 640 nm (⁴F_9/2→⁴I_11/2) signals, and the latter 640 nm (⁴G_7/2→⁴I_11/2), which were dependent on alumina.     

Highly enhanced luminescence of SrB4O7:Eu phosphor prepared by the combustion method using glycine as fuel

Eu²⁺ ion doped into SrB₄O₇ matrix was prepared by combustion method heated at 900 °C in air, using urea (U) or glycine (G) as fuels in different ratios (U100, A10, A25, G10, G25, G75, and G100). In some compositions, ammonium acetate (AA) was used to reduce the exothermicity of combustion reaction. X-ray diffraction and luminescence spectroscopy were used to characterize the material. The high intense emission band at 367 nm is assigned to 4f⁶5d → 4f⁷(⁸S_7/2) transition arisen from divalent europium ion. It is observed that the interconfigurational transition is dependent on the molar ratio of glycine:urea fuels. Glycine fuel favors Eu²⁺ formation in SrB₄O₇ host lattice prepared by combustion method.     

Energy transfer luminescence in (Eu,Nd) : tellurite glass

Here, we bring out an infrared transmitting new optical glass based on TeO₂ added with AlF₃ and LiF, containing dual rare earth ions (Eu³⁺,Nd³⁺) as the dopants with a purpose to examine their luminescence and also the decay times pertaining to a prominent transition of Eu³⁺ (⁵D₀ → ⁷F₂ at 615 nm) as a function of temperature both in the presence and absence of Nd³⁺ ions. The energy transfer rates (W_tr), critical distances (R₀) and transfer efficiencies (η_tr) have been evaluated based on the measured lifetime data of this glass.     

Thermoluminescence of Tb doped Gd2O2S phosphor

Thermoluminescence (TL) of gadolinium oxysulfide activated with terbium (Gd₂O₂S:Tb) is investigated. The glow curves of Gd₂O₂S:Tb phosphor recorded in the temperature range of 93–500 K with a heating rate of 0.52 K s⁻¹ shows five prominent glow peaks. Comparison of the glow curves exhibited by different samples prepared with varying firing conditions reveals some interesting results. In this phosphor capture centers are mainly formed due to variable valency activators, trace impurities and point defects, which create defects in the sub-lattice. The observed TL spectra suggest a multiplicity of electron and hole traps. The main peak that observed at 150 K is attributed to point defects arising out of sulfur vacancies. These vacancies give rise to electron traps, which are found to be associated with terbium centers. This is confirmed by the monochromatic glow curves observed at wavelengths corresponding to the characteristic terbium emission (⁵D₃–⁷F_n, ⁵D₄–⁷F_n). Removal of this glow peak under H₂S firing indicates the localized character of the concerned centers.     

Structure, nucleation and Eu luminescence in alkaline earth rare earth borate glass

In La₂O₃-MO-B₂O₃ ternary system, various glasses/ glass ceramics with M=Ca, Sr and Ba have been prepared. In this ternary system, homogeneous nucleation occuring in the B₂O₃ melt appears to be the cause for the formation of nanocrystallites, hence glass ceramics. The nucleation process is very much dependent on the alkaline earth used viz., with smaller alkaline earths like Ca, boron prefers (BO₄)⁵⁻ tetrahedral coordination with oxygen, while in the case of bigger alkaline earths like Ba and Sr, (BO₃)³⁻ triangular coordination seems to be predominant. Eu³⁺ in this glass system yields intense ⁵D₀→⁷F_j emission. A cursory view on the dependence of the various Judd-Ofelt parameters (Ω_k) indicates that Ω₂ parameter is very much dependent on the immediate vicinity of the luminescent ion (Eu³⁺) while Ω₄ is not. Various results based on these are discussed.     

Yb3+,Tb3+共掺杂Sr2B2O5荧光粉的制备及其下转换发光性能的研究

采用高温固相法合成了Tb³⁺, Yb³⁺共掺杂的Sr₂B₂O₅荧光粉。通过X射线衍射(XRD)和荧光光谱(PL)对样品的物相结构和发光性质进行了表征。XRD结果表明, 合成样品为单斜结构的Sr₂B₂O₅相。分别使用543 nm和980 nm的监测波长, 得到的激发光谱均在354 nm、374 nm处有较强的激发峰, 其中374 nm处最强, 说明Sr₂B₂O₅荧光材料在近紫外光区对太阳光有很强的吸收; 在374 nm( Tb³⁺:⁷F₆→⁵D₃) 紫外光激发下, 观察到Tb³⁺: ⁵D₄→⁷F_J ( J = 6, 5, 4, 3) 可见光区发射光, 并检测到Yb³⁺: ²F_5/2→²F_7/2的近红外发射光。通过研究激发光谱和发射光谱与Yb³⁺掺杂浓度的关系, 发现在单斜晶体Sr₂B₂O₅中, Yb³⁺具有很高的猝灭浓度。     

Preparation and photoluminescence properties of Eu-doped Ga2O3 nanorods

GaOOH:Eu³⁺ nanorods with different aspect ratios were prepared by hydrothermal method at 140 °C. - and β-Ga₂O₃:Eu³⁺ were converted from as-prepared GaOOH:Eu³⁺ particles by calcination at 500 and 850 °C, respectively. The products were characterized with X-ray diffraction (XRD), transmission electron microscope (TEM) and photoluminescence (PL). Results show that solution pH values play a key role in the formation of the GaOOH:Eu³⁺ powders with different morphologies and - and β-Ga₂:Eu³⁺ inherit the morphology of GaOOH:Eu³⁺ exactly. The photoluminescence characteristics of β-Ga₂O₃:Eu³⁺ were also investigated. Experimental results reveal that the color purity of β-Ga₂O₃:Eu³⁺ nanorods with high aspect ratio is enhanced in comparison with β-Ga₂O₃:Eu³⁺ nanorods with low aspect ratio.     

Blue, green and 0.8 μm Tm, Ho doped upconversion laser glasses, sensitized by Yb

To obtain efficient upconversion laser glass, the optical properties of Tm³⁺ and Ho³⁺ were investigated in various glasses. Fluoride glass was selected as base glass for upconversion. The efficient upconversion fluorescences corresponding to the ¹G₄→³H₆ and ³H₄→³H₆ transitions of Tm³⁺ and the ⁵S₂→⁵I₈ transition of Ho³⁺ were observed in Yb³⁺-Tm³⁺ and Yb³⁺-Ho³⁺ doped aluminozircofluoride glasses excited at 980 nm. The very stronge blue and green emission light can be observed visually. The upconversion processes observed were two-photon processes for ³F₄→³H₆, ⁵S₂→⁵I₈ transitions and three-photon processes for the ¹G₄→³H₆ transition and can be described by a rate equation model. The energy transfer and energy back-transfer were analyzed in Yb³⁺-Tm³⁺ and Yb³⁺-Ho³⁺ systems. The relationship between emission intensity, pumping intensity and dopant concentrations is described using a rate equation model and shows good agreement with experiments. The dynamics of excited state ( ) is also analyzed with the diffusion-limited model based on Yokota-Tanimoto theory.     

Improved optical photoluminescence by charge compensation in the phosphor system CaMoO4:Eu

It has been found that charge compensated CaMoO₄:Eu³⁺ phosphors show greatly enhanced red emission under 393 and 467 nm-excitation, compared with CaMoO₄:Eu³⁺ without charge compensation. Two approaches to charge compensation, (a) 2Ca²⁺ → Eu³⁺ + M⁺, where M⁺ is a monovalent cation like Li⁺, Na⁺ and K⁺ acting as a charge compensator; (b) 3Ca²⁺ → 2Eu³⁺ + vacancy, are investigated. The influence of sintering temperature and Eu³⁺ concentration on the luminescent property of phosphor samples is also discussed.     

Highly stable persistent spectral hole burning in Eu ions doped oxy-fluoride glasses of 30CaF2–10Al2O3–60B2O3

High temperature persistent spectral hole burning up to room temperature has been observed in Eu³⁺ ions doped oxy-fluoride glasses with a composition of 30CaF₂–10Al₂O₃–60B₂O₃ (mol%) melted in a reducing atmosphere. The hole stability was studied through light-induced hole refilling and temperature cycling experiments. The burned holes survive thermal cycling to 300 K due to a high barrier height of 0.69 eV in the sample.     

Long lasting phosphorescence of Sr4Al14O25:Eu,Dy thin films by magnetron sputtering

This paper reports the preparation process and the long lasting phosphorescence of the Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ thin films obtained by magnetron sputtering. Phosphorescence was achieved by annealing the films in reducing atmosphere. Sr₄Al₁₄O₂₅ thin film was obtained when the films were treated at 1200 °C, while SrAl₂O₄ was generated as the intermediate phase during the annealing process. Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ film generated an emission at 485 nm, and SrAl₂O₄:Eu²⁺,Dy³⁺ film showed an emission peaking at 515 nm. Afterglow characteristics were observed for both films, and Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ film showed a better afterglow property than the SrAl₂O₄:Eu²⁺,Dy³⁺ film due to a deeper trap level and a higher trap concentration formed in the thin films.     

Charge states and optical transitions of vanadium in Bi4Ge3O12 identified by MCD and ODMR

The spectroscopic properties of V-doped Bi₄Ge₃O₁₂ have been investigated in detail via several complementary techniques bringing a series of consistent results. The optical absorption spectrum of annealed samples is strongly modified under UV-illumination and the initial state can be restored optically with visible light. Optical absorption and magnetic circular dichroism (MCD) demonstrate that a diamagnetic defect is partly destroyed during UV-illumination while a paramagnetic one is created. The latter shows a very characteristic S-shaped MCD pattern in the near-IR, which is readily assigned to the ²E→²T₂ internal transition of tetragonal V⁴⁺ centers at the Ge sites. This assignment was further confirmed by optically detected magnetic resonance (ODMR), via the change of the MCD under microwaves at 35 GHz. The g tensor of V⁴⁺ was found to be anisotropic with principal values g_||=1.81±0.03 and g=1.94±0.02. Two additional MCD bands in the visible spectral region could be attributed to V⁴⁺ via ODMR measurements. Ionization thresholds for holes (V⁵⁺) and electrons (V⁴⁺) were determined by optical absorption experiments and the V^4+/5+ donor level was positioned 1.9 eV below the conduction band. The presence of the V^4+/3+ acceptor state in the forbidden band is also suggested.     

Preparation, patterning and luminescent properties of nanocrystalline Gd2O3:A (A=Eu, Dy, Sm, Er) phosphor films via Pechini sol–gel soft lithography

Nanocrystalline Gd₂O₃:A (A=Eu³⁺, Dy³⁺, Sm³⁺, Er³⁺) phosphor films and their patterning were fabricated by a Pechini sol–gel process combined with a soft lithography. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical microscopy, UV/vis transmission and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 500 °C and that the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free non-patterned phosphor films were obtained by optimizing the composition of the coating sol, which mainly consisted of grains with an average size of 70 nm and a thickness of 550 nm. Using micro-molding in capillaries technique, we obtained homogeneous and defects-free patterned gel and crystalline phosphor films with different stripe widths (5, 10, 20 and 50 μm). Significant shrinkage (50%) was observed in the patterned films during the heat treatment process. The doped rare earth ions (A) showed their characteristic emission in crystalline Gd₂O₃ phosphor films due to an efficient energy transfer from Gd₂O₃ host to them. Both the lifetimes and PL intensity of the rare earth ions increased with increasing the annealing temperature from 500 to 900 °C, and the optimum concentrations for Eu³⁺, Dy³⁺, Sm³⁺, Er³⁺ were determined to be 5, 0.25, 1 and 1.5 mol% of Gd³⁺ in Gd₂O₃ films, respectively.     

Enhancement of Er I13/2 population in Y2O3 by energy transfer to Ce

We report measurements of the energy transfer between Er³⁺ and Ce³⁺ in Y₂O₃. The transition between the Er^{3+ 4}I_11/2 and ⁴I_13/2 excited states can be stimulated by energy transfer to Ce³⁺, augmenting the population in the ⁴I_13/2 state at the expense of that in the ⁴I_11/2 state. Experiments were performed on Y₂O₃ planar waveguides doped with 0.2 at.% erbium and 0–0.42 at.% cerium by ion implantation. From measurements of Er³⁺ decay rates as a function of cerium concentration we derive an energy transfer rate constant of 1.3×10⁻¹⁸ cm³/s. The efficiency of the energy transfer amounts to 0.47 at 0.42 at.% cerium. The energy transfer rate constant measured in Y₂O₃ is two times smaller for Er³⁺→Ce³⁺ than that for Er³⁺→Eu³⁺ in the same material.