Reactive Atmosphere Processing Research Articles

Vacuum Ultraviolet Spectroscopic Properties in Gd3+-Eu3+ Ions Pair Doped MYF4 (M = Li, Na, and K)

LiYF4, NaYF4, and KYF4 doped with Gd3+-Eu3+ ion pairs synthesised by soft route (wet) chemical technique tracked by Reactive Atmosphere Process (RAP). The phase purity of every synthesized material is verified using the X-ray Diffraction (XRD) method. The photoluminescence excitation (PLE) and photoluminescence emission (PL) properties are examined in ultra-violet (UV) and vacuum ultraviolet (VUV) regions. A new type of photon harvesting (cutting) process is studied in the synthesized phosphors. The Quantum Cutting (QC) is observed only in host LiYF4 doped with Gd3+-Eu3+ Phosphor.

Improvement of quantum efficiency through Gd3+ to Eu3+ energy transfer in YF3 phosphor.

This paper reports the energy transfer from Gd3+ to Eu3+ in YF3 and the consequent downconversion luminescence for the YF3 :Gd3+ , Eu3+ fluoride phosphor. The phosphor was synthesized using a soft chemical route, followed by a reactive atmosphere process. Because of the wide band gap in YF3 and the correct energy site for 8 S7/2 -6 GJ transitions of Gd3+ ions, fluoride YF3 doped with Gd3+ -Eu3+ were studied in their vacuum-ultraviolet (VUV) spectral regions. Powder X-ray diffraction (XRD) analysis showed the structural purity of YF3 . VUV excitation and emission properties were explored using a VUV synchrotron radiation beam line. Downconversion of energy from VUV (157 nm) to visible light with quantum efficiency c. 189% was seen. This YF3 :Gd3+ , Eu3+ phosphor would be an option for mercury-free fluorescence lamps.

K(Sr1−xEux)2Cl5 scintillation material obtained using Eu2O3 dissolution in the growth chloride melt

The peculiarities of direct incorporation of Eu2+ (via Eu2O3) in KCl-SrCl2 (1:1.99) melt for the growth of Eu2+-activated scintillation material of K(Sr0.995Eu0.005)2Cl5 composition were studied. When added to the chloride melt at 973 K Eu2O3 starts to transform into EuOCl immediately and the process is essentially incomplete. The complete dissolution of Eu oxocompounds (Eu2O3, EuOCl) in the melt was provided by the application of the carbochlorination process (the action of CCl4 vapor) which is a special case of the reactive atmosphere processing (RAP). A scintillation material of K(Sr0.995Eu0.005)2Cl5 composition was grown from the obtained melt with an application of the Bridgman technique. The boule included long opaque end sections and transparent medium section with the composition of K(Sr0.995Eu0.005)2Cl5. The luminescence studies of the obtained samples confirmed coexistence of both Eu2+ and Eu3+ in the growth melt. The non-isomorphic Eu3+ is displaced to the top section of the boule as a result of directional crystallization. An amount of KI was added to the growth melt to provide complete reduction of Eu3+ into Eu2+. Scintillation parameters of all the obtained crystals are close: the relative light yield values are ca.70% vs. NaI:Tl and the energy resolution is within 8–9%.

Luminescence of Eu 2+ in some fluorides prepared by reactive atmosphere processing

When phosphors are prepared by conventional solid-state route by heating in air, usually unwanted impurities like OH −, O 2 −, etc., get incorporated. Such impurities can be quite harmful to the luminescence processes. Especially, fluorides are highly susceptible to hydrolysis. It is necessary to use highly sophisticated procedures like high vacuum and HF or CF 4 atmosphere for preparation of fluoride based phosphors. It is shown that using a simple wet chemical process and a modified reactive atmosphere processing (RAP) technique, fluorides showing intense Eu 2+ photoluminescence can be prepared.

Luminescent properties of nanostructured Dy3+- and Tm3+-doped lanthanum chloride prepared by reactive atmosphere processing of sol-gel derived lanthanum hydroxide

Dy 3+ - and Tm3+-doped lanthanum chloride was prepared via reactive atmosphere processing (RAP) of sol-gel derived hydroxide powders. The low-phonon energy chloride host facilitated the 1.3-μm emission from Dy3+ and the 1.2- and 1.4-μm emissions from Tm3+. The emission intensities of the Dy3+ and Tm3+ ions increased logarithmically with increasing RAP temperature. The dependence of emission intensities and lifetimes on the rare-earth (RE) concentration was also investigated. The emission intensity was found to increase up to 1 mole % RE for both ions. Luminescence quenching was observed for concentrations exceeding 1 mole % for Tm3+ and 0.1 mole % for Dy3+.

Crystal growth of metal fluorides for CO 2 laser operation : II. Optimization of the reactive atmosphere process (RAP) choice

A series of RAP reactions is considered for the 10 μm transparent metal halides. These RAP actions are independent of the metal in the halide. Comparing non-RAP which uses only HF(g), the RAP actions may be ordered in terms of superiority based on the entropy. Of the five RAP actions chosen (A)–(E), it is shown that the order is, C 2F 4(g)>NF 3(g)>CF 4(g)>COF 2(g)>SF 6(g), before any metal was considered. The superiority over non-RAP is demonstrated with both yttrium, lanthanum, and thorium as examples.

Crystal growth of metal fluorides for CO 2 laser operation I. The necessity of the RAP approach

The 10 μm transparency of halides addresses directly its oxide content. The conversion from oxide to fluoride must have Δ G≪0. HF(g) is different from the other hydrogen halides because its Δ G of formation is larger than that of H 2O(g). Decrease in the hydrolysis of RF 3 (R=rare earth) influences the crystal phase stability and the tendency of the crystal to crack. The base-to-acid behavior of +3 rare earths provides quantitative support. HF(g) and RAP (reactive atmosphere process) CF 4(g) formations of YF 3 from Y 2O 3 are given in detail. This indifference to HF(g) is reported also in the congruent growth of CaF 2, SrF 2, and BaF 2. The explanation is seen in ZrF 4, HfF 4, and ThF 4. Although RAP does not use HF(g), it permits the congruent growth of good-quality single crystals with very low H 2O(g) content.

Er3+-doped multicomponent silicate glass planar waveguides prepared by sol-gel processing

Erbium doped silica-titania planar waveguides, co-doped with ytterbium and aluminum, have been prepared by sol-gel processing, using multilayer spin-coating deposition on silicon or silica glass substrates. The Er3+ doping level varied between 0 and 2 at.%, while Yb3+ varied from 0 to 3 at.%. Aluminum was incorporated up to 15 at.% Al and it was found to have no significant effect on the refractive index of the silica-titania (80 : 20 mol%) matrix. The Er3+ fluorescence emission was flat within ±0.5 dB, between 1520 and 1560 nm. The corresponding 4I13/2 metastable level lifetime was found to decrease from 6.1 to 3.5 ms, as the Er concentration increased from 0.1 to 0.5 at.%, for films co-doped with 0.5 at.% Yb and 10 at.% Al and the fluorescence decay was essentially single exponential below a Er quenching concentration of 0.5 at.% (1.1 × 1020 ions/cm3). The lifetime appears to be limited by Er-Er interactions at higher rare-earth ion concentrations and by residual OH species in the sol-gel derived waveguides. Vacuum heat treatment at a temperature near 570°C was somewhat effective in increasing the Er fluorescence lifetime, whereas reactive atmosphere processing in CCl4 or Cl2 at a similar temperature appeared to be less effective.

The influence of reactive atmosphere processing on the crystallisation kinetics of GaF 3/InF 3 based glasses

Gallium–indium fluoride based glasses are one of the lowest phonon energy hosts for Pr-ion doped fibre amplifiers. However, to date the fabrication of low background loss fibres have been proved difficult. In the present investigation, GaF 3/InF 3 based glasses are prepared under the controlled reactive atmosphere of SF 6, HF and N 2 gas mixture. The devitrification characteristics of glass samples prepared in a range of reactive-atmospheres (RA) have been studied using differential scanning calorimetry. From the isothermal data, the time–temperature–transformation curves have been compared for various reactive-atmosphere processing (RAP) conditions and, the influence of RAP conditions on the glass stability is discussed. Loss in multimode fibres (~135 μm) drawn from the glass rods processed under RAP conditions are compared as a function of processing conditions. The measured loss values are reported in 0.5 to 2.0 μm wavelength regime.

Reactive atmosphere synthesis of sol-gel heavy metal fluoride glasses

A glass based on ZrF4 was synthesized by a combination of sol-gel and reactive atmosphere processing. Infrared spectroscopy and combustion analysis show that the fluorination process reduces the concentration of organic and hydroxide impurities. Chemical changes have occurred during fluorination; this is indicated by different x-ray diffraction traces and crystallization characteristics for the fluorinated sample compared to the oxide gel product. Chemical analysis from x-ray fluorescence indicates that the fluorinated gel is chemically similar to a melted glass of the same composition. Differential scanning calorimetry gives a glass transition temperature of 290 °C and a crystallization temperature of 390 °C. These values are consistent with those expected for a fluoride glass prepared by conventional methods.

Reactive Atmosphere Processing of Fluoride Glasses

Reactive Atmosphere Processing of Fluoride Glasses

Spectral properties of Nd 3+ in aluminophosphate glasses

The spectral properties of laser glasses in the system R 2O(MO)·Al 2O 2·Ln 2O 3·P 2O 5(R = Li, Na, K; M = Ca, Sr, Ba; Ln 2O 3 = Nd 2O 3 + La 2O 3), at a high Nd 3+ ion doping concentration of 1 × 10 21 ions/cm 3, were studied. Fe 2O 3 and other common transition metal oxide impurities were less than 10 ppm, and the absorption coefficient at 3.5 μm caused by OH − was below 1.0 cm −1 after removing the hydroxyl groups thoroughly by reactive atmosphere processing (RAP). Absorption and fluorescence spectra were measured at each composition. The effective linewidth was determined from the emission spectrum. The stimulated emission cross section for the 4 F 3 2 − 4 I 11 2 transition was calculated using the Judd-Ofelt model and the modified Deutschbein method. The results show that the influence of Al 2O 3 in phosphate glasses on fluorescence lifetime is much less than that in silicate glasses, and that both the fluorescence lifetime and the stimulated emission cross section decrease with increasing attraction between the alkali or alkaline-earth ions and oxygen. From the spectral and thermomechanical properties measured it is concluded that high Al 2O 3 containing aluminophosphate glasses with a high stimulated emission cross section of 3.3 × 10 −20 cm 2, a fluorescence lifetime of 180 μs at 10 21 Nd 3+ ions/cm 3 amd a thermal expansion coefficient of 80 × 10 −7 °C −1 can be obtained from these systems.

Synthesis and Characterisation of Heavy Metal Fluoride Glasses and Fibres

AbstractThe fabrication of optical fibres based on fluoride glasses has required the development of novel preparation techniques. Some of these techniques are based on methods used to prepare multicomponent oxide glass fibres although some have been developed specially for fluoride glasses. This paper will review such processes as glove-box melting, reactive atmosphere processing, and rapid quenching; show how these have been used to prepare fluoride glass fibres with losses down to 2.6 dB/km at 2.6 μm; and discuss remaining problems with the glass.

Nd:YAG quantum efficiency and related radiative properties

Measured quantum efficiencies of ten different Nd:YAG crystals show a variation from 0.47 to 0.87. In phototropic crystals, the quantum efficiency can be degraded by color center formation or improved by bleaching. Color center bleaching occurs by oxidation, using a high-temperature reactive atmosphere process to control crystal defects related to hydroxyl impurities. Ion-ion and ion-lattice interaction effects are examined for further evidence of Nd/sup 3+/ fluorescence quenching centers. Fluorescence rates, nonequivalent crystal field (NCF) effects, line broadening, Nd/sup +3/ lattice-defect interactions, and their temperature dependences are studied. Nd/sup 3+/ site perturbations occur in all crystal samples. Five NCF Nd/sup 3+/ sites show 6 cm/sup -1/ site-to-site Stark level shifts at liquid helium temperatures. Smaller scale shifts are characteristic of particular samples. While the crystals examined show individual differences, only hydroxyl-related coloration provides specific evidence of quenching centers. >

Reactive atmosphere processing of oxides (Part II)

The application of the reactive atmosphere process (RAP) to rare-earth oxides to suppress OH − impurity introduction is extended to the reduction of the higher oxide. A marked difference in the action of H 2 and CO is shown in the reduction of Tb 4O 7 to Tb 2O 3.

Water-free fused silica for laser windows made by the reactive atmosphere process

We have produced by the reactive atmosphere process (RAP) a new form of fused silica that is nearly free (of the order of 1 ppm) of water-derived impurities (OH−, H+). This RAP-fused silica is a vitreous form of the cristobalite crystal phase of SiO2 and not the quartz phase. Therefore, it is called “fused cristobalite”. This fused cristobalite exhibits simultaneously increased resistance to nuclear radiation, with no damage up to 10 Mrad (of 60Co gamma irradiation), and greatly increased IR transparency due to the lack of water absorption at the 2.73 μm OH stretch vibrational band. We present absorption measurements in the near-IR comparing our RAP-fused cristobalite with seven types of commercial fused sillica.

Reactive Atmosphere Processing of Fluoride Glasses

Reactive Atmosphere Processing of Fluoride Glasses

Effect of RAP purification on materials characterization

The purpose of a reactive atmosphere process (RAP) is to remove impurities, especially, polyatomic anion impurities, the most difficult of which is OH -. The latter, a pseudo-halide, is shown to be close in property to the fluoride. The two are far removed in reactivity and stability from the other halides. Thermodynamic arguments are presented to demonstrate that the practice of using the respective hydrogen halide gas as the sole RAP agent does not meet the defined objective of RAP. The criterion for the use of halogen as the RAP agent to clean up OH - impurity from metal oxides is given. The unusually large activity coefficient of OH - which influences melting behavior and solid-solid transitions is also shown to exert a limiting role on the purity of vapor-transported films. The unusually low electron affinity of OH - is made the basis of a model for color-center formation.

Dehydration of fluoride glasses by NF3processing

Reactive atmosphere processing with a NF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> gas is employed in the preparation of fluoride glasses to remove hydroxides in the glasses. The hydroxides are effectively removed by NF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> processing without any resultant increase in the scattering.

Elimination of Complex Ions in Fluoride Glasses by NF3 Processing

The influence of complex ions (NH4+, CO32-, NO3-, SO42- and PO43-) in fluoride glasses on absorption loss is investigated. To remove these ions, reactive atmosphere processing with NF3 has been applied. NH4+, CO32-, NO3- and SO42- are effectively eliminated by the NF3 processing.