Upeonversion Luminescence of Er3＋, Tin3＋ and Yb3＋ Co-doped Gd3Ga5O12 Nanocrystals

A series of Er3+,Tm3+ and Yb3+ doped Gd3Ga5O12 nanocrystals were prepared by a combustion method.The X-ray diffraction(XRD),field emission scanning electron microscope(FESEM)and upconversion(UC)emission spectra were used to characterize the samples.The results of XRD indicate that Gd3Ga5O12:Er3+,Tm3+,Yb3+ nanocrystals with cubic phase can be obtained.Under the excitation of a 980 nm laser,the different rare earth ions doped Gd3Ga5O12 nanocrystals show upconversion luminescence involving the green emission attributed to the 2H11/2→4I15/2,4S3/2→4I15/2 transitions of Er3+ ions,respectively,the red emissions assigned to the 4F9/2→4I15/2 transitions of Er3+ ions and the 1G4→3F4 as well as 3F2,3→3H6 transitions of Tm3+ ions,respectively,the blue emission attributed to 1G4→3H6 transitions of Tm3+ions,and the near-infrared assigned to the 3H4→3H6 transitions of Tm3+ ions.The CIE coordinates for the samples are calculated.The dependence of their upconversion luminescence properties on Yb3+ ion concentration is investigated.     

Preparation and upconversion luminescence of YVO4：Er^3＋,Yb^3＋

YVO_4:Er~(3+),Yb~(3+) with varying Yb~(3+) concentrations were prepared by a precipitation method.The results of X-ray diffraction (XRD) show that all the samples have a tetragonal zircon structure;the calculated average crystallite sizes are in the range of 14-22 nm.The lattice constants and cell volume of the samples decrease slightly with the increase in Yb~(3+) concentration.The upconversion luminescence spectra of all the samples were studied under 980 nm laser excitation.The strong green emission i...     

La , Li＋ Precipitation processes and luminescence properties of ZnO： 3＋ nanoparticles

ZnO:La3+ ,Li+ nanoparticles were successfully prepared by co-precipitation, citric acid-assisted co-precipitation, co-precipitation combined solid-state reaction and thermal decomposition method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and luminescence spectrophotometry were employed to characterize the crystal phases, particle sizes and luminescence properties of the as-prepared nanopowders. The results indicate that all the prepared samples crystallize in a hexagonal wurtzite structure. The ZnO:La 3+ ,Li+ prepared by citric acid-assisted co-precipitation method has a particle size of about 80 nm, which is the smallest among all the samples. Fluorescence (FL) spectra of all samples exhibit three typical emissions: a violet one centered at around 400 nm, blue around 450 nm and 466 nm, and weak green near 520 nm. But the samples prepared by co-precipitation method show a strong and wide green light emission located at about 500 nm. The ZnO:La 3+ ,Li+ nanoparticles synthesized by the co-precipitation method demonstrate relatively the strongest emission intensity.     

Effects of Heat-treatment Temperature on Eu^3＋ and Li^＋ Co-doped ZnO Photoluminescence by Sol-gel Process

The photoluminescence （PL） characteristics of Eu^3＋ and Li^＋ co-doped ZnO PL materials against heat-treatment temperature were discussed. The PL xerogel and powder samples were prepared by solgel process. The emission spectra of all samples showed two broad bands peaking at 590 nm and 620 nm under UV-Vis excitation. But the relative intensity of red PL （620 nm） was much greater than that of green PL （590 nm） of the same sample, that s to say, the red color was the main luminescence. With heat-treatment temperature increase, the two kinds of colors PL intensity decreased, and both the red and green PL intensity of the xerogel samples was much greater than those of powder samples respectively. The XRD patterns revealed that Eu^3＋ ions were successfully incorporated in ZnO crystals in xerogel samples. When heat-treatment temperature reached 350 ℃, the Eu^3＋ began to separate out of the ZnO crystals and Eu2O3 crystals came into being. When the powder sample was subjected to UV-Vis excitation, the energy transfered from the host ZnO emission to Eu^3＋ became weaker than the xerogel sample.     

Single crystal β-Ga2O3: Cr grown by floating zone technique and its optical properties

β-Ga2O3 Cr single crystals were grown by floating zone technique. Absorption spectra and fluorescence spectra were measured at room temperature. The values of field splitting parameter Dq and Racah parameter B were obtained by the peak values of absorption spectra. The value 10Dq/B=23.14 manifests that in -Ga2O3 crystals Cr3 ions are influenced by low energy crystal field. After high temperature annealing in air, the Cr3 intrinsic emission was enhanced and the green luminescence disappeared. The strong and broad 691 nm emission was obtained at 420 nm excitation due to the electron transition occurred from 4T2 to 4A2. The studies manifest that the β-Ga2O3 crystals have the potential application for tunable laser.     

Infrared-to-green upconversion properties of Er^3＋/Yb^3＋ co-doped TeO2-TiO2-K2O glasses upon excitation with 976 nm lasers diode

The energy transfer and upconversion of Er^3＋/Yb^3＋ co-doped TeO2-TiO2-K2O glasses upon excitation with 976 nm lasers diode were studied. The tellurite glasses were prepared by conventional melting methods. Their optical properties and sensitization upconversion spectra were performed. The dependence of green upconversion lu- minescence intensity on the mole ratio of Yb^3＋ to Er^3＋ and Er^3＋ concentration were discussed in detail. When the mole ratio of Yb^3＋ to Er^3＋ is 25/1 and Er^3＋ concentration is 0.1% （mole fraction）, or when the mole ratio of Yb^3＋ to Er^3＋ is 10/1 and Er^3＋ concentration is 0.15 %, the optimal upconversion luminescence intensity is obtained. The obtained glasses can be one of the potential candidates for lasers-diode pumping microchip solid-state lasers.     

Soft chemical synthesis and luminescence properties of red long-lasting phosphors Y202S：Sm3＋

Sm3＋-activated Y2028 red phosphors were prepared by the combustion method and microemulsion method at the first time. X-ray characterization and electron diffraction show that, Y202S：Sm3＋, Ti4＋, Mg2＋ samples prepared by these two methods are pure hexagonal crystals in structure with a trivial change due to dopants. Scanning electron microscopy （SEM） results show that the product presents an almond-like sheet in uniform size. Under the excitation of 269 nm ultraviolet light, Y202S：Sm3＋ samples fabricated by these two methods exhibit three main groups of red emission lines located at 564, 604, and 656 nm, respectively, which are attributed to the transitions of 4G5/2 →6H5/2, 4G~/2 →6H7/2, 4G5/2 →6H9/2, respectively. The samples prepared by microemulsion are seven times higher in fluorescent emission intensity and half time longer in afterglow time than that prepared by combustion.     

Synthesis of Polycrystalline Yb:Gd_3Ga_5O_(12) Nanopowders by Homogeneous Precipitation Method

The Ytterbium doped gadolinium gallium garnet [Yb3+:Gd3Ga5O12, Yb:GGG] precursor powders were synthesized via homogeneous precipitation method using Yb2O3, Ga2O3, Gd2O3 and ammonium bicarbonate [NH4HCO3] as precipitator, and ammonium sulfate [(NH4)2SO4] as additive. The evolution of phase composition and micro-structure of the powders were characterized by TG- DTA, XRD, IR, and TEM. The results indicate that all precursor powders completely transform to Yb:GGG phase by calcining at 900 ℃ for 8 h, the resultant powders are well dispersed and have smaller particle size approximately 80 nm owing to the electrostatic effect.     

Controlling synthesis and host sensitized Eu~(3+) emissions of K_5Gd_9F_(32) and GdF_3

By controlling the reactant ratios, hydrothermal time, hydrothermal temperatures, p H values of the prepared solutions, and the concentrations of K3C6H5O7·2H2O, 1 mol% Eu3+ doped cubic phase of K5Gd9F32 and/or orthorhombic phase of Gd F3 micro/nanocrystals have been synthesized based on a hydrothermal method. For comparison, the sample was also synthesized by a co-precipitation method. The samples were characterized by X-ray diffraction(XRD) patterns, field emission scanning electron microscopy(FE-SEM) images, energy-dispersive spectroscopy(EDS) spectra, and photoluminescence(PL) excitation and emission spectra. By host Gd3+ sensitizing, the Eu3+ presents relatively strong emissions. The energy transfers from host Gd3+ to doping Eu3+ are observed in all the samples and the energy transfer plays an important role in the emission of Eu3+. Acting as a probe, the Eu3+ presents its distinct optical properties in the samples.     

Preparation and Luminescent Properties of Eu^3＋ Doped Calcium Phosphate Nanocrystalline

The nanocrystalline Eu^3＋ doped calcium phosphate was prepared by calcining precursors, which were got by precipitation method combined with ultrasound treatment and some polysaccharide. The existence of Eu^3＋ inhibited the reaction of Na^＋ ion and SO4^2- radical with apatite and resulted in the transformation of HAP to β- TCP by replacing the calcium ions. The strongest excitation peak was at 393 nm, and other lower peaks were at 361 nm, 375 nm, 381 nm, 418nm. The strongest emission spectrum appeared at about 618nm. The emission peak （579 nm） showed that Eu^3＋ ions distributed on Ca^2＋ sites of the apatitic structure.     

Preparation and Upconversion Luminescence of Nanocrystalline Gd2O3:Er3+,Yb3+

Nanocrystalline Gd1.77 Yb0.2Er0.03O3 samples were prepared by combustion and precipitation methods.Structures and upconversion luminescence properties of samples were studied.The results of XRD show that all samples are cubic structure,the average crystallite size could be calculated as 23 nm and 39 nm.respectively.The lattice constants were obtained.The FT-IR spectra were measured to investigate the vibrational feature of the samples.Upconversion luminescence spectra of samples under 980 nm laser excitation were investigated.The strong red emission of samples were observed,and attributed to 4F9/2→4I15/2 transitions of Er3+ ions,the emission intensity for sample synthesized by precipitation method is stronger compared to that of combustion method. The possible upconversion luminescence mechanisms in nanocrystalline Gd1.77Yb0.2Er0.03O3were discussed.     

Preparation and optical properties of Er<Superscript>3+</Superscript>: Na<Subscript>2</Subscript>O-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> transparent glass-ceramics

Na₂O-Al₂O₃-SiO₂ glass-ceramics doped with Er³⁺ ions were synthesized by the conventional melt quenching technique at a low melting temperature. The samples were characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis-NIR scanning spectrophotometry, and fluorescence spectrometry. The results show that the main crystalline phase of glass-ceramics is nepheline.The best heat-treatment process is at 520 °C for 2 h. Because the up-conversion luminescence and near infrared luminescence properties of glass doped with Eu³⁺ are studied in detail.     

Crystallization and luminescence properties of Sm<Superscript>3+</Superscript>-doped SrO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> glass-ceramics

The Sm³⁺-doped SrO-Al₂O₃-SiO₂ (SAS) glass-ceramics with excellent luminescence properties were prepared by batch melting and heat treatment. The crystallization behavior and luminescent properties of the glass-ceramics were investigated by DTA, XRD, SEM and luminescence spectroscopy. The results indicate that the crystal phase precipitated in this system is monocelsian (SrAl₂Si₂O₈) and with the increase of nucleation/crystallization temperature, the crystallite increases from 66 % to 79 %. The Sm³⁺-doped SAS glass-ceramics emit green, orange and red lights centered at 565, 605, 650 and 715 nm under the excitation of 475 nm blue light which can be assigned to the ⁴G_5/2→⁶ H _j/2 (j=5, 7, 9, 11) transitions of Sm³⁺, respectively. Besides, by increasing the crystallization temperature or the concentration of Sm³⁺, the emission lights of the samples located at 565, 605 and 650 nm are intensified significantly. The present results demonstrate that the Sm³⁺-doped SAS glass-ceramics are promising luminescence materials for white LED devices by fine controlling and combining of these three green, orange and red lights in appropriate proportion.     

Frequency up-conversion luminescence properties and mechanism of Tm<Superscript>3+</Superscript>/Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> co-doped oxyfluorogermanate glasses

Oxyfluoride glasses were developed with composition 60GeO 2 ·10AlF 3 ·25BaF 2 ·(1.95-x)GdF 3 · 3YbF 3 ·0.05TmF 3 ·xErF 3 (x=0.02,0.05,0.08,0.11,0.14,0.17)in mole percent.Intense blue(476 nm),green(524 and 546 nm)and red(658 nm)emissions which identified from the 1G 4 →3H 6 transition of Tm3+and the(2H 11/2 ,4S 3/2 )→4I 15/2 ,4F 9/2 →4I 15/2 transitions of Er3+,respectively,were simultaneously observed under 980 nm excitation at room temperature.The results show that multicolor luminescence including white l...     

Interaction of rare earth ions in Sr<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript>: Eu<Superscript>2+</Superscript>, Dy<Superscript>3+</Superscript> material

To discuss the function of Eu and Dy and their interaction in Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ long afterglow material, the Eu and Dy single doped and their co-doped Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ were prepared. The samples were characterized by X-ray diffraction (XRD), decay curves, photoluminescence (PL), and thermoluminescence (TL). The results indicate that Sr₂MgSi₂O₇: Eu has afterglow properties, and the doping of Eu ion in Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ can lower the depth of traps. Eu ion can not only serve as luminescence center, but also produce traps in the matrix, meanwhile, it also exerts certain influences on the traps produced by Dy in Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺. The Dy ion can not act as luminescence center but relates to the change of the traps in the Sr₂MgSi₂O₇ matrix.     

Synthesis and luminescence of nano fluorescent powder of Y<Subscript>4</Subscript>Al<Subscript>2</Subscript>O<Subscript>9</Subscript>: Eu<Superscript>3+</Superscript>

Nano fluorescent powder of Y₄Al₂O₉: Eu³⁺ was synthesized by sol-gel method. The XRD shows that the product prepared at 900°C is pure-phase Y₄Al₂O₉: Eu³⁺. The Y₄Al₂O₉ powder is nano-size crystal testified by BF and ED analysis of TEM. The grain diameter of Y₄Al₂O₉ is in the range between 20 and 50nm, and its average is 30 nm. The luminescent spectra show that Eu³⁺ ious occupy two kinds of sites in Y₄Al₂O₉ crystal lattice. One is in the strict inversion center, and the other is in off lying inversion center. When excited with UV light (λ=254nm), Y₄Al₂O₉: Eu³⁺ exhibits an orange emission bond at λ=590 nm due to the⁵D_o→⁷F₁ transition and a red emission band at λ=610 nm due to⁵D_o→⁷F₂ transition. YUAN Xi-ming: Born in 1951 Funded by Key Scientific and Technological Project of Hubei Province (2001 AA102A03)     

The effect of OH~- groups on the spectroscopic properties of erbium-doped tellurite glasses

With the rapid development of computer networks and other data-transmitting ser-vices, the demand for the increase of transmission capacity of the long distance trans-mission system is urgent. However, the conventional SiO2-based EDFA is limited for its small bandwidth. The Er3+-doped tellurite glass exhibits a larger stimulated-emission cross section and a broader emission bandwidth at the third communication window (1.55 μm) than that of silicate, phosphate, and germanate glasses, which c…     

Roles of Eu^2＋, Dy^3＋ Ions in Persistent Luminescence of Strontium Aluminates Phosphors

The polycrystalline Eu^2＋ and Dy ^3＋ co-doped strontium aluminates SrAl2O4： Eu^2＋, Dy^3＋ with different compositions were prepared by solid state reactions. The UV-excited photoluminescence, persistent luminescence and thermo-luminescence were studied and compared. Results show that the doped Eu^2＋ ion in SrAl2O4： Eu^2＋, Dy^3＋ phosphors works as not only the UV-excited luminescent center but also the persistent luminescent center. The doped Dy^3＋ ion can hardly yield any luminescence under UV-excitation, but effectively enhance the persistent luminescence and thermo-luminescence of SrAl2O4： Eu^2＋. Dy^3＋ co-doping can help form electron traps with appropriate depth due to its suitable electro-negativity, and increase the density and depth of electron traps. Based on above observations, a persistent luminescence mechanism, electron transfer model, is proposed and illustrated.