Addition Of Alkali Ions Research Articles

Enhancements of luminescent properties of CaZrO3:Eu3+ by A+ (A = Li, Na, K)

CaZrO3:5%molEu3+ and CaZrO3:5%molEu3+/5mol%A+ (A = Li, Na, K) phosphors were synthesized by a solid state reaction. Effects of codoped alkali ions on luminescent properties of CaZrO3:5%molEu3+ was investigated. The XRD and FTIR measurements show that the all of synthesized phosphors have the same phase with pure CaZrO3. The excitation and emission spectra indicate that the codoped alkali ions enhance the Eu3+ emission intensity significantly. Moreover, the decay lifetime is also prolonged by the addition of alkali ions. The enhancements of luminescent properties for CaZrO3:5%molEu3+ can be attributed to the charge compensation and decrease of Ca2+ vacancies induced by the addition of alkali ions.

Alkali ions effect on optical properties of Tm3+, Yb3+ co-doped gadolinium tungstate phosphor

The Tm3+, Yb3+ co-doped gadolinium tungstate phosphor in presence and absence of alkali ions (i.e. Li+, Na+ and K+) has been synthesized through solid state reaction method. The structural characterization confirms the crystalline nature with coexistence of the two monoclinic phases. The phase fraction varies on addition of alkali ions. The Tm3+, Yb3+ co-doped phosphor emits intense blue and near infrared emissions centered at 472 and 793 nm due to 1G4 → 3H6 and 1G4 → 3H5 transitions, respectively and a weak red emission at 655 nm due to 1G4 → 3F4 transition of Tm3+ on excitation with 976 nm. The emission intensity of near infrared band dominates over the blue and red bands. When the alkali ions are added in the Tm3+, Yb3+ co-doped phosphor, the emission intensity of the bands is enhanced significantly due to modification in the local crystal field. The emission intensity is highest for K+ incorporation compared to Li+ and Na+ due to its occupancy at the interstitial sites. The lifetime measurement reveals an enhancement in the emission intensity. The pump power dependent emission intensity plots confirm the involvement of three photons for blue and two photons for red and NIR emissions. Thus, the Li+, Na+ and K+ incorporated Tm3+, Yb3+ co-doped gadolinium tungstate phosphor emitting intense blue and NIR radiations may be useful for photonic devices, bio-imaging and solar converters.

Effect of different alkali carbonate on the microstructure and photoluminescent properties of YInGe2O7:Eu3+ phosphors

For this study, different alkali carbonates (Li2CO3, Na2CO3, and K2CO3) were added to a Eu3+ activated YInGe2O7 phosphor synthesized using conventional sintering and microwave-assisted sintering. The morphology and photoluminescence properties of YInGe2O7:Eu3+ phosphors were investigated and discussed. When the alkali ions were introduced into YInGe2O7:Eu3+ phosphors, the excitation peaks of phosphors were shifted to a short wavelength because the addition of alkali ions may increase the oxygen vacancy in YInGe2O7:Eu3+ phosphors. Additionally, the best enhanced luminescent properties in YInGe2O7:Eu3+ phosphors were obtained through the addition of Li+ ion.

Catalytically active Au-O(OH)x-species stabilized by alkali ions on zeolites and mesoporous oxides.

We report that the addition of alkali ions (sodium or potassium) to gold on KLTL-zeolite and mesoporous MCM-41 silica stabilizes mononuclear gold in Au-O(OH)x-(Na or K) ensembles. This single-site gold species is active for the low-temperature (<200°C) water-gas shift (WGS) reaction. Unexpectedly, gold is thus similar to platinum in creating -O linkages with more than eight alkali ions and establishing an active site on various supports. The intrinsic activity of the single-site gold species is the same on irreducible supports as on reducible ceria, iron oxide, and titania supports, apparently all sharing a common, similarly structured gold active site. This finding paves the way for using earth-abundant supports to disperse and stabilize precious metal atoms with alkali additives for the WGS and potentially other fuel-processing reactions.

Enhancement of green long lasting phosphorescence in CaSnO3:Tb3+ by addition of alkali ions

Long lasting phosphors of CaSnO3:Tb3+ added alkali ions (Li+, Na+, K+) were prepared by solid-state reaction. The phosphorescence of samples consists of a group of green emission lines originating from 5D4→7FJ transitions of Tb3+. The afterglow spectra and concentration quenching behaviors of fluorescence were investigated in the Tb3+ mono-doped sample. The result shows the optimal doping concentration of Tb3+ is 0.3mol%. In the co-doped samples, the doping concentrations of Tb3+ and alkali ions are both at 0.3mol%. It is found from the afterglow decay curves that the introduction of alkali ions can prolong the phosphorescent lasting time and the sample of incorporating Na+ shows the best result. Tb3+ and alkali ions can substitute Ca2+ ions, acting as hole and electron traps, respectively. The thermoluminescence (TL) spectra are also investigated. The depths of traps for the mono- and co-doped samples are calculated to be 0.622, 0.541, 0.529 and 0.538eV, respectively. Moreover, the possible mechanism of the green long lasting phosphorescence is proposed based on the experiment results.

Different alkali carbonates on the microstructure and photoluminescence properties of BaY2ZnO5:Tb3+ phosphors prepared using the solid-state method

For this study, different alkali carbonates (Li2CO3, Na2CO3, and K2CO3) were added to a Tb3+ activated BaY2ZnO5 phosphor synthesized using the solid-state reaction, and the morphology and photoluminescence properties of BaY2ZnO5:Tb3+ phosphors are investigated and discussed. When BaY2ZnO5:Tb3+ phosphors to which alkali carbonates were added were sintered at 1250°C for 12h, X-ray powder diffraction analysis showed that the unreacted Y2O3 raw material decreased, and scanning electron microscopy (SEM) showed that large particle sizes and necking shapes were obtained. Emission intensities decreased, and the wavelengths of the excitation peaks changed when alkali carbonates were added to BaY2ZnO5:Tb3+ phosphors. The excitation peaks of phosphors prepared with alkali carbonates were shifted to a short wavelength because the addition of alkali ions may increase the oxygen vacancy in BaY2ZnO5:Tb3+ phosphors and change the photoluminescence properties. The CIE chromaticity (x,y) is (0.35,0.55), and does not change with the addition of alkali carbonates.

Silica-encapsulated platinum catalysts for the low-temperature water-gas shift reaction

Encapsulated platinum in the form of core–shell Pt@SiO2 prepared by reverse microemulsion, can be rendered catalytically active for the low-temperature water-gas shift (WGS) reaction by the addition of alkali ions during the synthesis steps or by impregnation of the dried (uncalcined) core–shell materials. We report that positively charged platinum species, embedded throughout the silica shell and stabilized by the alkali ions are the active sites for the WGS reaction. Water dissociation and hydroxyl regeneration take place on the Na-promoted Pt–Ox sites. It is shown by cyclic CO-TPR experiments with intermittent ambient rehydration that the activity remains constant, and the onset temperature of the reaction is the same, ∼150°C, with cycling. The apparent activation energies for the WGS reaction in realistic fuel gas mixtures over the various encapsulated Pt-based catalysts evaluated here and those on other supports are all in the same range, 70±5kJ/mol. Hence any difference in the reaction rates between the open- and encapsulated-Pt catalysts is attributed to their different number of active sites accessible to the reactants. The Pt-Na@SiO2 catalyst structures show remarkable stability with time-on-stream at 350°C.

Spectroscopic investigation and optical characterization of novel highly thulium doped tellurite glasses

In this paper, optical properties of 75TeO 2 –20ZnO–5Na 2 O host glass doped with concentration of Tm 3+ up to 10 %mol were studied in order to assess the most suitable rare earth content for short cavity fiber lasers. Raman spectroscopy revealed a change in the glass structure while increasing Tm 3+ content, similar to the well known addition of alkali ions in a glass. Influence of the fabrication process on the OH − content was determined by FTIR measurements. Refractive index of Tm 3+ doped tellurite glasses was measured at five different wavelengths ranging from 533 nm to 1533 nm. Lifetime and emission spectra measurements of the Tm 3+ doped tellurite glasses are reported.

Calcination of Metatitanic Acid to Titanium Dioxide White Pigments

In the sulfate process for the production of TiO2 white pigments, gel-like metatitanic acid is calcined in a rotary kiln to microcrystals of the rutile polymorph. This process is monitored by the addition of alkali ions, Al3+, phosphate and rutile nuclei. During the last decade, a scientific understanding has developed how these additives influence the solid-state reactions of the material in the kiln, i.e., crystal growth, transformation of anatase to rutile, incorporation of dopants and aggregation of crystals. This review describes mechanisms and kinetics of the reactions, using modern concepts of solid state and surface chemistry and physics. It also describes the effects of the reactions on the quality of the calciner discharge in upgrading and for the customer, i.e., the grindability to pigment particles, their light-scattering properties and photocatalytic activity. The principles of the additive functions revealed here may be used in process engineering of other powder reactions as well as in particle chemistry and nanotechnology in general.

Preparation and characterization of Li +-modified Ca xPb 1− xTiO 3 film for humidity sensor

A novel active element for a humidity sensor based on Ca 2+-doped PbTiO 3 perovskite ceramic film has been prepared by the sol–gel technique. The addition of alkali ions, especially, Li + dopant was found to be beneficial to the improvement of the humidity-sensitive characteristic. The resulting film modified by Li + calcined at 850°C for 1 h was characterized by X-ray diffraction (XRD) and transmission electronic microscope (TEM). The results obtained show that the crystalline size and the lattice distortion are the key factors that influence the humidity properties. At room temperature, and 100 Hz frequency, the variations of sensor’s resistance values ( R) are higher than three orders of magnitude over the working relative humidity ( ϕ) range, from 8 to 93.5% RH. The curves log R versus ϕ of the designed sensor show excellent linearity, high sensitivity ( R 8% RH / R 93% RH >10 3 ), minimal hysteresis (<±2% RH) and rapid response (<8 s).

NMR studies on rapidly solidified SiO 2Al 2O 3 and SiO 2Al 2O 3Na 2O-glasses

27Al and 29Si MAS NMR studies were performed on roller-quenched SiO 2Al 2O 3-glasses with Al 2O 3 contents ranging from 10 to 60 mol% and on SiO 2Al 2O 3Na 2O glasses containing 10 mol% Al 2O 3 and 2.5 to 10 mol% Na 2O. Pure aluminium silicate glasses show NMR peaks at 0, 30 and 60 ppm. The frequency distribution of the different Al-sites is not affected by the glass composition. In glasses of the system SiO 2Al 2O 3Na 2O the 30 ppm peak decreases to zero as the Na 2O content increases. The 30 ppm peak is assigned to distorted triclustered AlO-tetrahedra, rather than to fivefold coordinated Al. Triclustering of tetrahedra may provide for charge neutrality in glasses with molar excess of Al 2O 3 over Na 2O. As charge balance is increasingly achieved by addition of alkali ions, the tendency of tetrahedral triclustering is reduced, reflected by the disappearance of the 30 ppm peak in glasses containing ≥ 7.5 mol% Na 2O.

Selective partial oxidation of light alkanes over alkali-ion-modified silica-supported vanadium oxides excited with visible light

Alkali-ion (Na+, K+, and Rb+)-modified V2O5/SiO2 irradiated with visible light catalyzes the partial oxidation of 2-methylpropane to form mainly propanone and 2-methylpropan-2-ol. The addition of alkali ions to V2O5/SiO2 is essential to generate the active site that can be excited with visible light. It is confirmed that there are two types of reaction paths for the formation of 2-methylpropan-2-ol.

Luminescence of Ce 3+ in alkaline earth chloride lattices

The luminescence properties of cerium in alkaline earth (Ca, Sr, Ba) chlorides have been studied. Cerium emits in these matrices in the UV-region (330–400 nm) and the excitation bands locate at 220–330 nm. The emission shows a slight shift to shorter wavelengths when the host cation changes from calcium to strontium and barium although these simple trends are difficult to see because SrCl 2: Ce has several sites for the emitting ion. The addition of alkali ions (Na or K) for charge compensation enhances the luminescence but has only a minor effect on the wavelengths. Concentration quenching does not take place for Ce concentrations less than 5–10 mol%.

Ceramic sensors for humidity detection: the state-of-the-art and future developments

The possible applications of humidity sensors in automated systems for environmental control encompass many industrial and domestic fields. Very different operating temperatures and a variety of humidity ranges are needed for these purposes. The different humidity-sensing mechanisms and operating principles identified for ceramics are reviewed. Ceramic humidity sensors are divided into ionic, electronic, solid-electrolyte and rectifying-junction types. Examples of the performance of some ceramic sensors are presented. The correlation between the microstructure of ceramic materials and their humidity-sensitive electrical response is discussed. The improvement of the performance of ionic-type humidity sensors by the addition of alkali ions is explained in terms of influence on the microstructure and on the intrinsic impedance. The recent trend towards the miniaturization and integration of sensors on a single chip requires the production of ceramic films. Ceramic thin films prepared by sol-gel or sputtering processes are investigated. The results obtained on the humidity sensitivity of pn semiconducting oxide heterocontacts are also reported.

Selective Photooxidation of Propane to Propanone over Alkali-ion-modified Silica-supported Vanadium Oxides

The addition of alkali ions (Na, K and Rb) to silica-supported vanadium oxide results in the formation of surface vanadate species which is excited by the light with wavelengths of around 400 nm. Propanone was selectively formed from propane and oxygen over alkali-ion-modified silica-supported vanadium oxides by the photoirradiation of light with wavelengths of λ > 390 nm.

Basic Sites on Alkali Ion-added Zeolite

Abstract The X type zeolites containing alkali ions in excess of ion exchange capacity exhibited high catalytic activity for 1-butene isomerization; the reaction proceeded at 273 K. Temperature programed desorption (TPD) of adsorbed CO2 confirmed that strongly basic sites were generated by addition of alkali ions. Alkali metal oxides formed in the zeolite cavities are considered to possess strongly basic sites and to act as the catalytic sites.

Factors controlling the resealing of the membrane of human erythrocyte ghosts after hypotonic hemolysis

In accordance with former observations of Hoffman (1962a), ghost populations obtained by hypotonic hemolysis and subsequent restoration of isotonicity by the addition of alkali salts, were found to be composed of 3 types of ghosts. For our purposes it was useful to distinguish between: (1) ghosts which reseal immediately after hemolysis (type I); these ghosts are incapable of incorporating alkali ions which are added after hemolysis; (2) ghosts which reseal after the addition of alkali ions (type II); salt added to the hemolysate becomes trapped inside these ghosts in the course of the resealing process at temperatures above 0°C; and (3) ghosts which remain leaky regardless of the experimental condition (type III). The discrimination between the various types of ghosts was partly achieved by a kinetic method first devised by Hoffman (1962a), and partly by sucrose density gradient centrifugation. The relative sizes of the 3 fractions depend on the temperature at which hemolysis took place and on the time interval which elapsed between hemolysis and the addition of salt. At 37°C the resealing process is fast. Many of the ghosts reseal before salt can be added to the hemolysate. Hence, the fraction of type I ghosts is high after hemolysis at that temperature. At 0°C resealing is extremely slow. Hence, salt which has been added to the hemolysate at that temperature will enter the ghosts and become trapped during subsequent incubation at 37°C. There are no ghosts of type I and many ghosts of type II (about 60%). Regardless of the temperature at hemolysis, there are always ghosts which do not reseal even after prolonged incubation at 37°C. A method has been designed which permits the preparation of homogeneous populations of type II ghosts. Complexing agents (ATP, EDTA, 2,3-DPG) may prevent the resealing of the ghost membrane. However, they exert this effect only at elevated temperatures and when present in the medium at the instant of hemolysis. At 0°C, the presence of complexing agents in the medium at the instant of hemolysis has no effect on the subsequent resealing at 37°C. The recovery of the ghost membrane takes place in spite of the continued presence of the agents and eventually leads to trapping of these agents inside the resealed ghosts. The experiments support the contention that the complexing agents interact with a membrane constituent which is neither accessible from the inner nor from the outer surface of the cell membrane but becomes exposed during the hemolytic event when the complexing agents penetrate across the membrane. Apparently, at low tempertrures membrane ligands are more successful in competing with the added complexing agents for this constituent than at higher temperatures. Extending former observations of Hoffman, we found that not only Mg++ but also Ca++ facilitates the resealing process. Perhaps one or the other of the two alkaline earth ions is the membrane constituent which normally participates in the maintenance of the integrity of the red blood cell membrane.