Co-doped Aluminate Research Articles

Boron and Aluminum Codoped ZnO Transparent Conducting Films with High Electrical Stability

We suggest boron (B) and aluminum (Al) codoped ZnO (BAZO) transparent conducting thin films with high electrical stability for photovoltaic applications. The resistivity of widely used Al-doped ZnO (AZO) film decreased slightly by B doping. Above all, the resistivity of BAZO (4.9 at. % boron) increased by less than 1.5 times, whereas that of reference AZO film increased by over than 8 times after thermal annealing in atmospheric air. The carrier concentration and Hall mobility were much less degraded in BAZO films. X-ray photoelectron spectroscopy analysis showed that the peak portion related with chemisorbed oxygen at 100 nm-inside of the film was suppressed in BAZO film compared with AZO film. The B atoms would restrain the oxygen permeation into the film, which made the process of oxygen chemisorption inactive.

Effects of aluminum co-doping on photoluminescence properties of Ce 3+-doped SiO 2 glasses

SiO 2 glasses co-doped with Al 3+ ions were prepared by a sol-gel method by holding 0.5% of Ce 3+ ions constant and varying the Al 3+ ions concentrations. Thermal stability, the structural, chemical and the optical properties of the samples were studied by using differential scanning calorimetric (DSC), thermo gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), UV-vis spectroscopy and photoluminescence spectroscopy (PL). The DSC and TGA of samples depicted that the presence of dopant and co-dopant decreased the endothermic peak temperature and the yield respectively. SEM images showed that the particles were in the nano-range and spherical in shape. The XRD showed that all the samples were amorphous. The UV absorption measurements indicated that the presence of Al 3+ ions significantly reduced the SiO 2 absorption band, increased the absorbance intensity of SiO 2 and decreased the transmittance as compared to the presence of the Ce 3+ ions alone. The photoluminescence results displayed an optimum increase in luminescence intensity when the ratio of Al: Ce was 10:1 and further increase in aluminum content quenched the luminous intensity.

Photoluminescence of Tb 3+/Ce 3+ co-doped aluminum oxynitride powders

Aluminum oxynitride(AlON) phosphors co-doped by Tb 3+ and Ce 3+ were synthesized by nitridation of the precursor which was co-precipitated from Al(NO 3) 3 solution and nanosized carbon black at 1750 °C for 2 "hrs" in flowing nitrogen atmosphere. The obtained AlON based powders were composed of polycrystalline spinel typed particles with sizes in the range of 1–3 μm. Under an excitation of 275 nm, it was found that co-doping of Ce 3+ could drastically enhance the luminescence of AlON:Tb 3+ powder by energy transfer. The product with 0.5 mol% Ce 3+ and 0.67 mol% Tb 3+ exhibited a strong broad green emission at 540 nm. The critical quenching concentration of Tb 3+ in AlON:0.5 mol% Ce 3+/xmol% Tb 3+ phosphor was determined to be 0.67 mol%. It was supposed that the mechanism of concentration quenching of Tb 3+ in AlON:0.5 mol% Ce 3+ xmol% Tb 3+ phosphor was dipole–dipole interaction.

Room-Temperature Ferromagnetism in Cobalt and Aluminum Co-Doping Tin Dioxide Diluted Magnetic Semiconductors

Sn0:897Co0:10Al0:003O2 diluted magnetic semiconductor films were grown on (100) silicon substrate by magnetron sputtering and then annealed at 300 � C and 500 � C for 1.5 h, respectively. Room temperature ferromagnetism was observed for the as-deposited film. The saturation magnetization (Ms) decreases as annealing temperature increases, and the value of Ms for the films annealed at 500 � C is about half of the value for the as-deposited films. The electrical resistivity of Sn0:897Co0:10Al0:003O2 drops in a range of 10 6 to 10 � � m with increasing the annealing temperature. The XRD and HRTEM investigation illustrates that no impurity phase and Co clusters exist in the films, indicating the ferromagnetism of the films is intrinsic. The F-center-mediated exchange model is adopted to explain the room-temperature ferromagnetism of the films. [doi:10.2320/matertrans.M2009373]

Anomalous Eu layer doping in Eu, Si co-doped aluminium nitride based phosphor and its direct observation

Eu, Si co-doped AlN shows blue luminescence by UV and electron excitation. However, it is not clear how Eu is located in a wurtzite AlN lattice as there is not enough space for a large Eu cation. In the present study, Eu, Si co-doped AlN is analyzed to elucidate the luminescent Eu center’s location and the role of co-dopant Si. The XRD shows that the lattice parameters decrease compared to Eu solely doped AlN and undoped AlN due to Si doping in the AlN lattice. The Eu solely doped product shows impurity phase contamination with a reddish body color. Si co-doping is essential for Eu incorporation into AlN. TEM-EDS and HAADF-STEM measurements clarify that Eu forms a single layer structure with the Si condensation between the AlN wurtzite blocks. Another Si layer condensation is observed at the half position between Eu layers. Electron diffraction shows that there is no apparent long range ordering of Eu layer. The XAFS study shows that all the Eu in the product has a divalent valence and that the bond distance to the first neighboring anion is long at 0.315(8) nm. This is in good agreement with the model structure and the blue emission property. This result indicates that layer type doping can be a used to design new phosphors.

Luminescence and X-ray Diffraction Studies of Rare Earth Doped Silica Sol-Gel Glass

We present recent work exploring the effects of aluminum co-doping on the luminescent properties of rare earth ions in sol-gel glasses. Using x-ray diffraction techniques we have identified the formation of aluminum rich nano-crystals in silica glass annealed to high temperatures. We discuss implications of these results in understanding the impact aluminum co-doping has on rare earth luminescence in sol-gel glass.

Codoping of aluminum and gallium with nitrogen in ZnO: A comparative first-principles investigation

We perform first-principles density-functional theory calculations to investigate the atomic structures and electronic properties of dopant complexes involving Al, Ga, and N in wurtzite ZnO. We find that both Al and Ga substituted on Zn sites act as single donors and exhibit a strong attractive interaction with a nitrogen acceptor located at the nearest-neighbor oxygen site in the same (0001) plane, forming passive (Al-N) and (Ga-N) complexes. These structures induce fully occupied defect states above the valence-band maximum of bulk ZnO. On introducing a higher concentration of nitrogen, (Al-2N) and (Ga-2N) complexes form. The additional N atom in these complexes prefers to occupy another nearest-neighbor site of the Al or the Ga atom, compared to being further away from it, and acts as an acceptor with ionization energies of 0.17 and 0.14 eV, respectively. These values are lower than the ionization energy of the single N acceptor, which is 0.33 eV. This indicates that (Al,N) and (Ga,N) codoping could increase the percentage of N dopants that are activated by ionization. The interaction between two (Al-N) complexes and the interaction between the (Al-2N) complex and a N atom (on a neighboring oxygen site) are very weak, indicating that the N concentration cannot be significantly increased by Al and N codoping or cluster doping. In contrast, two (Ga-N) complexes prefer to bind together in the same (0001) plane, implying that the passive complexes which create the impurity band could reach high concentration. The formation energy for (Ga-2N) is lower than (Al-2N) in the neutral and the negative charge states under most experimental conditions. Furthermore, the (Ga-2N) complex binds with additional N atoms located at nearest-neighbor O sites and therefore has a tendency to form clusters of (Ga-3N) and (Ga-4N). Under Zn-rich conditions and for an NO source of nitrogen, the cluster (Ga-3N) has a lower formation energy and lower transition levels compared to the (Ga-2N) complex; the (Ga-4N) complex has the lowest formation energy and the lowest $(0/1\ensuremath{-})$ transition energy among the (Ga,N) complexes. Our findings suggest that codoping of (Ga,N) could efficiently enhance the N dopant solubility with the NO source (rather than an ${\text{N}}_{2}$ source for nitrogen) and is likely to yield better $p$-type conductivity than (Al,N) codoping.

P- and n-Type Doping in SiC Sublimation Epitaxy Using Highly Doped Substrates

The co-doping of nitrogen and aluminum has been studied in the sublimation epitaxy growth process. It is shown that the doping may be tuned from n-type to p-type by effect of substrate doping, growth face and volume of the growth crucible. The co-doped layers show a nearly ideal I V characteristic and luminescence at room temperature.

Optical Properties of Tm-Er Codoped Aluminate Glasses

Transparent CaO-Al2O3-B2O3 glasses codoped with Tm3+ and Er3+ were prepared by melt quenching and subsequent heating. Optical absorption spectra revealed an ultraviolet to visible absorption band corresponding to a relative electronic transition of Tm3+ and Er3+. For Tm-only doped glasses, the 791-nm absorption line is prominent and also has comparable strength in Tm-Er codoped glasses. Both 405-nm and 791-nm wavelengths have been used as excitation sources to comparatively study the photoluminescence characteristics of Tm3+ and Er3+. Only Er3+ emission at 1528 nm has been observed under a pumping wavelength of 405 nm. However, both Tm3+ and Er3+ emission can be found with an excitation wavelength of 791 nm. It implies that 791 nm should be very e ective for pumping Tm-Er codoped aluminate glass for application in broadband optical waveguide ampli ers.

Multiple solution-doping in optical fibre fabrication II – Rare-earth and aluminium co-doping

This work is part of a study of solution-doping in Modified Chemical Vapour Deposition, as used for fabrication of specialty silica optical fibres. It has been shown in an earlier paper that multiple soakings of a porous silica soot layer with intermediate heat-treatment stages between soakings can be used to introduce high levels of aluminium into an optical fibre core. The present paper demonstrates that the same technique can be applied to doping a fibre core with the rare-earth erbium and to co-doping aluminium and erbium simultaneously. Dopant levels have been tracked through the various stages, from soaked soot layer to the sintered glass layer to the collapsed preform. Experimental data are presented for both erbium soaking and co-doping with aluminium and erbium. The role of aluminium in preventing rare-earth segregation is confirmed.

Spectroscopic properties of neodymium doped high silica glass and aluminum codoping effects on the enhancement of fluorescence emission

Nd3+-codoped and Al3+-Nd3+-codoped high silica glasses have been prepared by sintering nanoporous glasses impregnated with Nd3+ and Al3+ ions. The Judd–Ofelt intensity parameters Ω2,4,6 of Nd3+-doped high silica glasses were obtained and used to analyze aluminum codoping effects. Fluorescence properties of Nd3+-doped high silica glasses strongly depend on the Al3+ concentration. While Nd3+ ion absorption and emission intensities of obviously increase when aluminum is added to Nd3+-doped high silica glasses, fluorescence lifetimes decrease and aluminum codoping has almost no influence on the radiative quantum efficiencies. This indicates that aluminum codoping is responsible for an anti-quenching effect through a local modification of rare-earth environments rather than through physical cluster dispersion.

5D 3→ 7F J emission in terbium-doped sol–gel glasses

In silicate sol–gel glass doped with trivalent terbium, the intensity of violet and blue fluorescence from the 5D 3 level is highly dependent on terbium concentration, on the presence of Al 3+ co-dopant, and on annealing conditions. Evidence is presented that aluminum co-doping prevents rare earth clusters from forming, and also modifies the coupling of rare earth ions to the local environment. 5D 3 emission is observed in glasses annealed at 750 °C, and increases in intensity with increasing annealing time and with higher temperature. This behavior is shown to be due to the removal of residual hydroxyl ions.

Structural and spectroscopic analysis of [formula omitted]-Al 2O 3 to [formula omitted]-Al 2O 3-CoAl 2O 4 phase transition

Co-doped alumina powders were synthesized by means of the polymeric precursor method to obtain ceramic pigments. The effect of different contents of Co 2+ on phase transition γ to α -Al 2O 3 and appearing of CoAl 2O 4 spinel were studied by means of X-ray diffraction. A partial phase diagram of the system CoAl 2O 3 was proposed from these data by means of determination of the percentages of these phases according to the calcining temperature. Critical particle size to phase transition was determined by means of calculations of crystallite size and determination of superficial area through the BET method. UV–vis spectroscopy of the samples allow to compare the band shift with the phase transition. Besides, a study of thermal stability and intensity of the blue coloration of the synthesized powders with the presence of cobalt in relation to the calcining temperature was accomplished and compared to the phase transition. The results show that the higher blue color intensity was obtained for the powders with Co-doped γ -Al 2O 3 closest of phase transition to α - Al 2 O 3 + CoAl 2 O 4 .

Densification and Grain Growth of Fe‐Doped and Fe/Y Codoped Alumina: Effect of Fe Valency

The effect of iron and iron/yttrium codoping on the densification and grain growth of ultra high‐purity (99.995%) fine‐grained alumina has been studied. The experiments were carried out under both oxidizing (flowing air) and reducing conditions (N2/H2 mixture, pO2∼5.1 × 10−14). For studies carried out in air, relative to undoped alumina, the addition of 1000 ppm Fe was found to reduce the densification rate by a factor of 5 and also retard the grain growth rate. This result, which was consistent with tensile creep data obtained in a separate study, was attributed to the retardation of grain‐boundary diffusive processes by segregating Fe(III) ions. In contrast, under reducing conditions the 1000 ppm Fe‐ doped samples exhibited an increase in the densification rate of 2.5 orders of magnitude over that of the undoped samples. In the case of the codoped compositions (1000 ppm Fe/1000 ppm Y), for heat treatment in air, the densification behavior did not differ significantly from that of samples singly doped with Y (1000 ppm). However, under reducing conditions, the presence of the Fe2+ in the samples appeared to compensate for the retarding effect of the yttrium, such that the densification rate of the codoped samples was comparable with that of the undoped material. A mechanism based on compensating point defects is invoked to rationalize the more rapid kinetics under reducing conditions.

Mechanism of Persistent Luminescence in Eu2 + and Dy3 + Codoped Aluminate and Silicate Compounds

A mechanism of persistent luminescence that was proposed in 1996 for has been widely adopted to explain afterglow in many and codoped aluminates and silicates. The mechanism involves the thermally activated release of a hole from in its excited 5d state to the valence band which is subsequently trapped by . In this work the location of the lanthanide energy levels relative to the valence and conduction band of various compounds is presented. It is shown that the mechanism of persistent luminescence cannot be correct. An alternative model that involves the ionization of the 5d electron to conduction band states and subsequent trapping by is proposed. The level schemes are consistent, both qualitatively and quantitatively, with many observations regarding persistent luminescence. They also provide insight into the mechanism of thermal quenching of 5d-4f emission.

Aluminum co-doping of soda-lime silicate glasses: Effect on optical and spectroscopic properties

One of the limits of using silicate glasses as a host for Er 3+ is the emission bandwidth, which is smaller than in the case of other oxide glasses, such as phosphates and tellurites. The bandwidth can be increased by adding aluminum to the composition. Here we present an experimental investigation of the effect of increasing aluminum content on optical and spectroscopic properties of this glass. Glass samples were prepared by melting at 1550 °C reagent grade SiO 2, Al 2O 3, Na 2CO 3, K 2CO 3, CaCO 3, (NH 4) 3PO 4 and Er 2O 3; Al 2O 3 concentration ranged from 0.99 to 20 mol%. Both heating and cooling rates were equal to 0.17 °C s −1. Measurements of the fluorescence bandwidth were then made and as a function of alumina content. Judd–Ofelt analysis was performed and calculated radiative lifetimes were compared with experimental ones. Planar waveguides were also fabricated by using ion-exchange technology, and some optical properties measured by the prism coupling technique. These waveguides had losses of the order of 1 dB/cm at 635 nm.

Electrical and Physical Properties of Al and Nb Doped PbTiO<sub>3</sub> Ceramic Thin Films

A series of Pb(Ti1-xAlx)O3, Pb(Ti1-xNbx)O3 and Pb(Ti1-xAlx/2Nbx/2)O3 thin films were fabricated onto Pt/Ti/SiO2/Si(100) substrates using a chemical solution deposition process. The dielectric constant of the Pb(Ti1-xAlx)O3 thin films increased with increase of aluminum content, while a maximum dielectric constant value was observed for the Pb(Ti1-xNbx)O3 and Pb(Ti1 xAlx/2Nbx/2)O3 thin films when the doping contents were 10 and 20 mol%, respectively. The dielectric constant of the Pb(Ti0.8Al0.1Nb0.1)O3 thin film is about 600, being two times higher than those of Pb(Ti0.9Al0.1)O3 and Pb(Ti0.9Nb0.1)O3 thin films. The Pb(Ti0.8Al0.1Nb0.1)O3 thin film showed less than 10-7 A/cm2 current density at ±150 kV/cm, being superior to the leakage property of the PbTiO3, Pb(Ti0.9Al0.1)O3 and Pb(Ti0.9Nb0.1)O3 thin films. The co-doping of aluminum and niobium is more effective to increase the dielectric and ferroelectric properties as compared with the individual aluminum or niobium doping.

The effect of grain boundary phase on contact damage resistance of alumina ceramics

The effect of grain boundary phase on contact damage behavior is investigated in alumina ceramics. Four types of aluminas doped with MgO, anorthite (CaO·Al2O3·2SiO2), silica, and with both MgO and anorthite are prepared such that they have similar average grain size by adjusting sintering conditions. MgO-doped alumina composed of equiaxed grains shows brittle fracture behavior, and anorthite-doped alumina composed of elongated grains shows a quasi-plastic response under Hertzian sphere indentation. The co-doped alumina with MgO and anorthite, however, is damage tolerant even with its rounded grains, while silica-doped alumina with similar grain size and shape to anorthite-doped alumina shows abrupt strength degradation with low critical load for cone cracking. The damage behavior is discussed from the viewpoint of residual stress induced by thermal expansion mismatch between the grains and grain boundary phases. The damage tolerant behavior of alumina ceramics is significantly affected by the composition of grain boundary phase.

Bismuth- and aluminum-codoped germanium oxide glasses for super-broadband optical amplification.

Broadband infrared luminescence from bismuth-doped germanium oxide glasses prepared by a conventional melting-quenching technique was discovered. The absorption spectrum of the glasses covered a wide range from the visible to the near-infrared wavelength regions and consisted of five broad peaks below 370, 500, 700, 800, and 1000 nm. The fluorescence spectrum exhibited broadband characteristics (FWHM) greater than 300 nm with a maximum at 1300 nm pumped by an 808-nm laser. The fluorescence lifetime at room temperature decreased with increasing Bi2O3 concentration in the glass. Codoping of aluminum and bismuth was indispensable for the broadband infrared luminescence in GeO2:Bi, Al glass.

Transient and persistent spectral hole burning in Eu 3+-doped sol–gel produced SiO 2 glass

Transient and persistent spectral hole burning (TSHB and PSHB) experiments were performed on Eu 3+ ions in sol–gel SiO 2 glasses with aluminum co-doping. Differences in the hole burning behavior were observed among samples made from two organosilicate precursors that were annealed to a series of final temperatures. All glasses exhibited persistent spectral holes when annealed to 800°C but, as the annealing temperature was raised to 1000°C, an increasing number of Eu 3+ ions exhibited TSHB with a corresponding decrease in the number of ions showing PSHB behavior. The transient hole burning behavior is similar in nature to that observed for Eu 3+-doped silicate melt glass.