Effects of Bi doping on the optical properties of Er:Y2O3

The influences of Bi³⁺ doping on the optical properties of Er³⁺:Y₂O₃ are investigated under UV and IR excitations. The emission intensity of Er³⁺ is remarkably enhanced by the introduction of Bi³⁺ under both two excitations. The emission enhancement under UV excitation originates from the energy transfer from Bi³⁺ to Er³⁺, while under IR excitation it can be attributed to the modification of the local crystal field around the Er³⁺.     

Effect of Bi doping on the quenching concentration of H11/2/S3/2 level of Er

Bi³⁺ and Er³⁺ codoped Y₂O₃ was prepared by sol-gel method. The upconversion emission was investigated under 980 nm excitation. For samples without Bi³⁺, the quenching concentration of ²H_11/2/⁴S_3/2 level of Er³⁺ is 3.0 mol%. However, by 1.5 mol% Bi³⁺ doping the quenching concentration increases to 5.0 mol%; meanwhile, the green emission is enhanced 1.9 times. The results indicate that both the quenching concentration and the emission intensity of ²H_11/2/⁴S_3/2 level can be increased by Bi³⁺ doping.     

White light emission in Tm/Er/Yb tri-doped Y2O3 transparent ceramic

Tm³⁺/Er³⁺/Yb³⁺ triply doped Y₂O₃ transparent ceramics were fabricated by solid state reaction and characterized from the point of view of white light upconversion luminescence. All the samples exhibited high transparency not only in near-infrared band but also in visible region. Strong red (Er³⁺: ⁴F_9/2 → ⁴I_15/2), green (Er³⁺: ²H_11/2, ⁴S_3/2 → ⁴I_15/2) and blue (Tm³⁺: ¹G₄ → ³H₆) upconversion emissions have been observed under 980 nm excitation at room temperature. By varying the concentration of Er³⁺ ion, various colors of upconversion luminescence (pure blue, bluish green, pure green and yellowish green), including white light with CIE-X = 0.295 and CIE-Y = 0.312, can be easily achieved.     

Correlation between the surface state and optical properties of S6 site and C2 site in nanocrystalline Eu:Y2O3

Eu³⁺ doped Y₂O₃ nanocrystals are synthesized via precipitation and hydrothermal methods. With the increase of hydrothermal temperature, the number of surface states decreases when nanorods are formed. The decrease of surface states induces the increase in the ratio of S₆ site to C₂ site, and meanwhile results in the spectral red-shift of charge transfer band as well as the enhancement of red emission. The results indicate that the surface states and optical properties have close correlations.     

Ionic conductivity and Raman investigations on the phase transformations of Na4P2O7

The ionic conductivity and thermo-Raman spectra of anhydrous sodium pyrophosphate Na₄P₂O₇ were measured dynamically in the temperature range from 25 to 600 °C with a heating rate of 2 °C min⁻¹ to understand the structural evolution and phase transformation involved. The DSC thermogram was also measured in the same thermal process for the phase transformation investigation. The spectral variations observed in the thermo-Raman investigation indicated the transformation of Na₄P₂O₇ from low temperature phase () to high temperature phase () proceeded through pre-transitional region from 75 to 410 °C before the major orientational disorder at 420 °C and minor structural modifications at 511, 540 and 560 °C. The activation energies and enthalpies of the proposed phase transformations were determined. The possible mechanism for temperature dependent conductivity in Na₄P₂O₇ was discussed with the available data.     

Synthesis and optical properties of Yb0.6Y1.4O3 transparent ceramics

Transparent yttrium oxide ceramics doped with 30 at.% ytterbium were successfully produced by a combination of pre-sintering and hot isostatic pressing. The influence on the final transparency of different densification states and porosity configurations obtained by varying pre-sintering conditions were investigated by optical and electron microscopy. Our results show that densification prior to the final stage of sintering is necessary to limit final porosity. Samples showing open porosity were found to lead to pore entrapment because of the diffusion of argon inside the glass capsule during hot isostatic pressing. Transmittance measurements showed that the valence charge of the ytterbium ions was 3+ at the end of the process, indicating no effect of reduction when pre-sintering in vacuum was employed.     

Enhancement of upconversion luminescence of Y2O3:Er nanocrystals by codoping Li-Zn

The upconversion (UC) luminescence in sol-gel synthesized Li⁺, Zn²⁺, or Li⁺-Zn²⁺ codoped Y₂O₃:Er³⁺ nanocrystals were investigated under the excitation of a 970 nm diode laser. Compared to undoped Y₂O₃:Er³⁺ samples, proper doping of Li⁺-Zn²⁺ leads to an drastic increase of the UC luminescence centered at 560 nm by a factor of 28. The UC luminescence enhancement is a result of the increased lifetime of the intermediate state ⁴I_11/2 (Er). The intensity ratio of the green over red emissions (green/red) is also affected by the codoping of Zn²⁺, Li⁺ and Li⁺-Zn²⁺ ions. Our results demonstrated that the Li⁺-Zn²⁺ codoping in Y₂O₃:Er³⁺ phosphors produced remarkable enhancement of the UC luminescence and green/red ratio, making this nanocrystal a promising candidate for photonic and biological applications.     

Size dependent luminescence of nanocrystalline Y2O3:Eu and connection to temperature stimulus

In the emission spectra of nanocrystalline Y₂O₃:Eu with decreasing the particle size, the ⁵D₀-⁷F₀ transition of Eu³⁺ shifts towards blue. This size effect is explained by lattice expansion of the nanocrystallines, more precisely, by larger Eu-O distance. Meanwhile, increasing temperature also expands the lattice constant and shifts the emission peak to blue. Then nephelauxetic effect is employed to organize the size effect and temperature dependence. It is also introduced to indicate the change of Eu³⁺ coordination number in the nanosized phosphor. Based on the experimental results, possible applications of temperature sensing and stress mapping with Eu³⁺ doped nanocrystalline phosphors are proposed.     

Preparation, characterization and the electrogenerated chemiluminescence behavior of WO3 nanocrystals

The (WO₃)_NCs/Nafion film electrode was prepared by immobilizing the synthesized WO₃ NCs on the surface of a glassy carbon electrode (GCE) with the help of Nafion. The ECL emission of the electrode in aqueous solution was affected by the buffer solution with respect to the pH and composition. And the strongest ECL was observed in an NH₃-NH₄Cl buffer with pH being 8.2. Only a weak ECL peak at 1.14 V which was originated from the annihilation process between oxidized and reduced species of WO₃ NCs was found. By adding coreactant triproplamine (TPrA) in buffer solution, an additional ECL peak at 1.13 V which was attributed to the electron-transfer reaction between the oxidized WO₃ NCs and reduced intermediate of TPrA was observed. The (WO₃)_NCs/Nafion film electrode exhibits excellent ECL property and good stability, which would promote the potential application of WO₃ NCs as a luminescence material for solid-state ECL detection.     

Nano-sized Y2O3:Eu hollow spheres with enhanced photoluminescence properties

Nano-sized Y₂O₃:Eu³⁺ hollow spheres were fabricated via a facile strategy including preparation of the hollow precursor and a later calcination. Moreover, the growth process of these hollow spheres was monitored by time-dependent experiments and their luminescence properties were also intensively studied. The products exhibit strong red emitting at 613 nm under ultraviolet excitation and control experiments were carried out to optimize the synthetic conditions. It was found 850 °C calcination with 9 mol% doping level could give out the best photoluminescence performance. Moreover, a possible mechanism for the enhanced PL performance was also proposed based on the FT-IR investigation.     

Ba4In2−x(CO3)1+xO6−2.5x and Ba4In0.8Cu1.6(CO3)0.6O6.2—new indium oxycarbonates closely related to n=3 Ruddlesden–Popper phases

Investigations of phase relations in the Ba-rich part of the In₂O₃–BaO(CO₂)–CuO pseudo-ternary system at 900 °C have revealed the existence of new indium–copper oxycarbonate – Ba₄In_0.8Cu_1.6(CO₃)_0.6O_6.2. Rietveld refinement of the X-ray powder diffraction data combined with infrared studies gives evidence that this phase is a oxycarbonate crystallising in the tetragonal structure (space group I4/mmm) with unit cell parameters: a=4.0349(1) Å and c=29.8408(15) Å. In the binary part of the In₂O₃–BaO(CO₂) system we have identified the occurrence of Ba₄In_2−x(CO₃)_1+xO_6−2.5x oxycarbonate solid solution showing a crystal structure also described by I4/mmm space group, but with the unit cell parameters: a=4.1669(1) Å and c=29.3841(11) Å for x=1. The existence range of this phase, −0.153<x<0.4, includes chemical compositions of earlier found phases: Ba₅In_2+xO_8+0.5x with 0≤x≤0.45 (known as the -solid solution), as well as the binary Ba₄In₂O₇ phase. The crystal structures of both new oxycarbonates are isomorphic and related to n=3 member of the Ruddlesden–Popper family.     

Host-sensitized multicolor tunable luminescence of lanthanide ion doped one-dimensional YVO4 nano-crystals

We report the Na₂EDTA-assisted synthesis of the lanthanide (Ln³⁺) ion doped one-dimensional YVO₄ nanobelts and nanorods by a facile hydrothermal route. XRD, TEM, EDS and FTIR techniques are used to characterize the microstructures of the synthesized nano-crystals. The morphology-dependent luminescent behaviors of Eu³⁺:YVO₄ are systematically investigated. Under a single wavelength UV light excitation, the Ln³⁺:YVO₄ (Ln = Nd, Sm, Eu, Dy, Ho, Er, Tm, or Yb) nanorods exhibit visible to near-infrared (NIR) multicolor tunable luminescence via efficient host sensitization, while no emissions are detected for the Ce³⁺, Pr³⁺, or Tb³⁺ doped samples. Based on the results, possible mechanisms depicting the YVO₄ host sensitizing or quenching of lanthanide emissions are proposed.     

Citric based sol-gel synthesis and luminescence characteristics of CaLa2ZnO5:Euphosphors for blue LED excited white LEDs

A novel class of orange-red phosphors namely CaLa₂ZnO₅ (CLZ) doped with Eu³⁺ ions were prepared by adopting citrate based sol-gel method. Those were thoroughly characterized by means of XRD, SEM, Tg-DTA, photoluminescent (PL) spectral profiles. PL studies reveal that its emission intensity strongly depends on sintering temperature as well as the dopant ion (Eu³⁺) concentration. Eu³⁺ ion doped CaLa₂ZnO₅ phosphor has a strong excitation at 468 nm, which correspond to the popular emission line from a GaN based blue light-emitting diode (LED) chip. The influence of the preparation method on the luminescence property was studied by comparing the emission performance of phosphors prepared by sol-gel and solid-state reaction methods along with a commercial red phosphor Y₂O₂S:Eu³⁺. Thus, the intense red emission (⁵D₀ → ⁷F₂) of the Eu³⁺ doped CLZ phosphors under blue excitation suggests them to be a potential candidate for the production of white light by blue LEDs.     

Preparation and luminescent properties of europium-activated YInGe2O7 phosphors

Effects of precursor milling on phase evolution and morphology of mullite (3Al₂O₃·2SiO₂) processed by solid-state reaction have been investigated. Alumina and silica powders were used as starting materials and milling was taken place in a medium energy conventional ball mill and a high-energy planetary ball mill. Milling in a conventional ball mill although decreases mullite formation temperature by 200 °C, but does not considerably change mullite phase morphology. Use of a planetary ball mill after 40 h of milling showed to be much more effective in activating the oxide precursors, and mullitization temperature was reduced to below 900 °C. Whisker like mullite was formed after sintering at 1450 °C for 2 h and volume fraction of this structure was increased by increasing the milling time. XRD results showed that samples mechanically activated for 20 h in the planetary ball mill were fully transformed to mullite after sintering at 1450 °C, whereas Al₂O₃ and SiO₂ phases were still detected in the samples milled in the conventional ball mill for 20 h and then sintered at the same conditions.     

Ultraviolet and violet upconversion luminescence in Ho-doped Y2O3 ceramic induced by 532-nm CW laser

Ultraviolet and violet upconversion luminescence spectra of holmium-doped Y₂O₃ were produced under the excitation of a compact continues-wave 532 nm solid-state laser. Emissions around 306, 362, 412, 390 and 428 nm can be assigned to the transitions of ³D₃ → ⁵I_J (J = 8, 7, 6), ⁵G₄ → ⁵I₈ and ⁵G₅ → ⁵I₈, respectively. Power dependence and upconversion dynamics analysis demonstrated that both the energy transfer upconversion (ETU) and the excited state absorption (ESA) processes were involved in the population of ³D₃ state via the coupled intermediate states ⁵S₂/⁵F₄. Fluorescence spectra in the visible and infrared ranges showed that ⁵G₄ and ⁵G₅ states were populated by the ESA process from ⁵I₆ and ⁵I₇ states, respectively, while the ⁵I₆ and ⁵I₇ states were radiatively populated from the excited ⁵S₂/⁵F₄ states. Upconversion mechanisms have been evaluated based on a rate equation model.     

Synthesis and upconversion luminescence properties of monodisperse Y2O3:Yb, Ho spherical particles

Monodispersed spherical Y₂O₃:Yb, Ho upconversion luminescence (UCL) particles with sizes of 40-200 nm are prepared using a homogeneous precipitation method. It is found that aging time, varying between 90 and 10 min, has a profound influence on the precursor size, which systematically decreases from 230 nm to 50 nm. The precursor shows poor stability when aging time is 10 min, and the stability of precursor can be improved by increasing the urea concentration. The UCL spectra of Y₂O₃:Yb, Ho with different particle sizes are investigated. The results indicate that the integrated emission intensity ratio of green to red (R_green/red) exhibits a gradual decrease from 2.7 to 0.45 when the particle size decreases from 200 nm to 40 nm, and the possible reasons are evaluated.     

Effects of sucrose concentration on morphology and luminescence performance of Gd2O3:Eu nanocrystals

Red Gd₂O₃:Eu nanophosphors were prepared by novel sucrose-assisted combustion method. The sucrose hydrolysis and complexing procedures were discussed by the Fourier transform infrared spectroscopy (FTIR) analysis. The effect of sucrose-to-metal ratio (S:M) on morphology and luminescence intensity of Gd₂O₃:Eu nanocrystals were investigated. And the optimum ratio was found to be S:M = 7:1, as confirmed by the results of scanning electron microscope (SEM), transmission electron microscope (TEM) and photoluminescence (PL) measurements. The highest photoluminescence emission from the particles obtained at S:M = 7:1 was about 85% of the commercial red phosphors.     

Optical and thermal properties of P2O5-Na2O-CaO-Al2O3:CoO glasses doped with transition metals

The aim of this paper is to report the optical and thermal properties of V₂O₅ and CuO doped P₂O₅-Na₂O-CaO-Al₂O₃:CoO glasses so as to investigate their possible use in solar collection applications. The optical absorption spectra of the glasses at room temperature were in the spectral range of 200-1100 nm. The optical band gaps of the glass samples were determined for direct and indirect transitions. When transition metal ions doped to the base glass, the optical band gap decreased. Changes in the refractive indices vs. wavelength for all the specimens were also examined by spectroscopic ellipsometry. By measuring the heat capacities and thermal diffusion coefficients of the specimens at varying temperatures, their thermal conductivities were calculated to be in the 320-620 K temperature range. The obtained glasses seem to be promising materials and can be used in solar collector applications.     

Enhanced photoluminescence of BaMgAl10O17:Eu nanophosphor for PDP application

BaMgAl₁₀O₁₇:Eu²⁺ nanorods were synthesized by sol-gel technique, and their luminescent properties were investigated upon the irradiation of vacuum ultraviolet (VUV) light. By introducing surfactant cetyl-tri-methyl-ammonium bromide (CTAB) in sol-gel process and additional Mg²⁺ in the raw materials, the emission intensity and thermal stability of the nanophosphor were both enhanced. The above improvements made it possible that the nanosized BAM phosphor could be a good alternative for PDP application.     

Controllable synthesis of bifunctional NaYF4:Yb/Ho@SiO2/Au nanoparticles with upconversion luminescence and high X-ray attenuation

A novel type of bifunctional water-soluble NaYF₄:Yb³⁺/Ho³⁺@SiO₂/Au nanocomposite is fabricated by a facile layer-by-layer technology in which the mercapto-silica shell is used as the functional layer coating on the central NaYF₄:Yb³⁺/Ho³⁺ nanocrystals. Then by adjusting the mole ratio of the Au nanoparticles to the NaYF₄:Yb³⁺/Ho³⁺@SiO₂ nanoparticles, control of the gold loading on the upconversion nanocrystal surface is achieved. The fabricated nanocomposites inherit the excellent physical and chemical properties from their building blocks, simultaneously exhibiting upconversion luminescence and high X-ray attenuation and as well are easily modified with various molecules. These properties render the synthesized NaYF₄:Yb³⁺/Ho³⁺@SiO₂/Au nanocomposite not only useful as a multimodality contrast agent to increase the efficiency of molecular imaging but also has the potential of in situ curing of diseases.