Galvanoluminescence Research Articles

Effect of Pre-Anodized Film on Micro-Arc Oxidation Process of 6063 Aluminum Alloy.

In the current investigation, micro-arc oxidation (MAO) ceramic coatings on aluminum are galvanostatically synthesized at various processing stages in an alkaline silicate system. The resultant coatings are systematically investigated in terms of the following respects: The working voltage and surface sparking evolution over the studied course of MAO are recorded by the signal acquisition system and the real-time imaging, respectively; the phase composition, the surface morphology, and the polished cross-section of the coatings are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) assisted with an energy-dispersive X-ray spectrometer (EDS), respectively. In particular, with the help of a low-rate increase in working voltage, the evolution of the sparks, the energy consumption, and the microstructure development of aluminum in alkaline silicate electrolyte by pre-anodizing are systematically investigated. The results show that the pre-anodized film can accelerate the evolution process of MAO spark and shorten the reaction process in the early stage of MAO reaction, reducing energy consumption and improving the corrosion resistance of the MAO coating. The γ-Al2O3 phase content after pre-anodized is significantly increased in MAO coatings. In particular, the thicker the pre-anodized film (beyond 8 μm) was broken down and fragmentation thinning in the early stage of the MAO process with the presence of micro discharges. This is due to the fact that the electron transition will be released by the emission of radiative recombination and reveals obvious galvanoluminescence (GL) behavior on the surface of the pre-anodized film. Further, based on the present MAO coating microstructure, a model of coating growth after pre-anodized that evolves over time is proposed.

Light emission from electrodes under dielectrophoresis conditions

The use of fluorescence in microfluidic optical biodetection requires materials with low-background fluorescence to avoid influencing the desired optical signal with spurious light emission. For the same reason, spurious light emission from galvanoluminescence (GL) should be avoided when fluorescence is used in dielectrophoresis (DEP)-based biosensors. Use of non-noble metal electrodes such as indium tin oxide (ITO) in DEP devices is therefore a concern. We evaluate GL in the context of conditions typical of DEP devices. We experimentally show that use of ITO can result in GL. We also show that GL can be avoided, even with metals that demonstrate strong GL such as Al, by proper selection of operating frequency, which can be determined by measuring the impedance spectrum of the DEP device. In addition, we demonstrate that GL results in broadband emission for all of the salt solutions tested. Broadband emission implies that at least some of the light will pass through typical fluorescence filters if a device exhibits GL. We also show that Ni and Cr electrodes do not exhibit GL and may therefore be suitable as low-cost DEP electrodes.

Galvanoluminescence of oxide films during the anodization of titanium

In this paper, we have presented the results of our investigation of galvanoluminescence (GL) originating from oxide films obtained by anodization of titanium in alkaline solutions. For the first time we have measured weak GL during the anodization of titanium and found strong influence of sample's surface pretreatment, as well as anodizing conditions (current density and electrolyte temperature). GL is more intense for rougher titanium samples, higher current density, and higher temperature of electrolyte. Spectral characterization of GL showed that there are wide GL bands present mostly in the visible and near infrared spectral region. As the potential of anodization approaches the breakdown voltage, a numerous transient sparks appear superimposed on the GL.

Galvanoluminescence properties of porous oxide films formed by anodization of aluminum in malonic acid

The influence of anodic conditions on the intensity of galvanoluminescence (GL) and shape of the GL spectra of porous oxide films formed by aluminum anodization in malonic acid aqueous solution was investigated. We have showed that there are wide GL bands in the visible region of the spectrum and observed two dominant spectral peaks. The position as well as the relative ratio of the spectral peaks depends on the voltage of anodization and the temperature of electrolyte. Also, our results have showed that GL is more intense at lower temperature of electrolyte and higher current density. Comparison with GL spectra of porous oxide films in organic carboxylic electrolytes indicates the same type of luminescence centers responsible for GL in this type of electrolytes. Energy dispersive spectroscopy (EDS) as well as Infrared Fourier Transform (ATR-FTIR) spectroscopy confirmed the correlation between GL spectra and incorporation of carboxylic species during anodization in carboxylic acids.

Effect of aluminum annealing on the galvanoluminescence properties of anodic oxide films formed in organic electrolytes

The galvanoluminescence (GL) properties of anodic oxide films formed in organic electrolytes were investigated at different aluminum annealing temperatures. The results of the spectral measurements showed two different types of GL sources: carboxylate ions incorporated in oxide films during the anodization and the molecules AlH, AlO, Al 2, AlH 2, also formed during anodization process and already recognized in the case of inorganic electrolytes. The latter was related to gamma alumina crystalline regions formed by annealing of the aluminum samples at temperatures above 500 °C.

Nature of Galvanoluminescence of Oxide Films Formed by Aluminum Anodization in Inorganic Electrolytes

The presented results of our galvanoluminescence (GL) measurements of oxide films formed by anodization of high purity aluminum samples annealed at 550 °C in inorganic electrolytes show that the sudden rise in the formation of γ alumina crystalline regions is strongly related to the appearance of GL. We have recorded GL spectra and observed six intensive and broad emission band peaks around 430, 483, 544, 575, 601, and 648 nm. A semiquantitative analysis based on literature data on simple molecular species involving the Al atom, as well as those atoms whose presence is possible under given experimental conditions (hydrogen, oxygen, etc.) showed that GL could be caused by transitions in molecules AlH, AlO, Al2, and AlH2, possibly contained in the pores of the γ alumina crystal islands.

The galvanoluminescence spectra of barrier oxide films on aluminum formed in organic electrolytes

In this paper, for the first time we have presented the results of the galvanoluminescence (GL) spectra measurement obtained from barrier oxide films during aluminum anodization in various barrier film forming organic electrolytes (aqueous solution of citric acid, tartaric acid, malic acid, succinic acid and ammonium tartarate). Galvanoluminescence spectral measurements were performed utilizing spectrograph system based on the Intensified Charge Coupled Device (ICCD) camera, intended for time-resolved detection of GL phenomena dynamics. The spectra were recorded for different values of electrolyte temperature and anodization current density. We have showed that there are strong GL bands in the visible region and the shape of the spectra as well as peak intensity of the GL bands depend on the anodization voltage. The results cleraly indicate the existance of more then one type of GL centra or GL mechanisms in barrier films formed in organic electrolytes.

Light-Emitting-Diode-Based Light Source for Calibration of an Intensified Charge-Coupled Device Detection System Intended for Galvanoluminescence Measurements

A spectrally tunable light source utilizing three light-emitting diodes (LEDs) for calibration of a highly sensitive intensified charge-coupled device (ICCD) optical detection system intended for time-resolved galvanoluminescence (GL) measurements is described. The source has been conceived as a low-cost substitute for standard tungsten lamps usually used for relative and absolute calibration of optical detection systems. Three LEDs with different spectral characteristics in conjunction with a system of two integrating spheres as light mixers and light reducers are used. This construction provides control over the source spectrum by changing individual LED contributions. The use of integration spheres eliminated angular distribution of light intensities of LEDs as well as angular dependence of their spectral contributions. Moreover, by using the source we have avoided the problem of stray and diffuse light of higher wavelengths, as well as different light intensities for different wavelengths (up to three orders of magnitude in the range from 400 nm to 750 nm), which we have with standard tungsten lamps. A complete calibration procedure for the LED source and ICCD detection system is described. Finally, for the first time, we have performed time-resolved spectral GL measurements during aluminum anodization in porous film-forming electrolyte phosphoric acid in a transient regime. Two peaks at 425 nm and 595 nm are recognized, confirming the same mechanism of GL in both transient and steady-state regimes of anodization.

The galvanoluminescence spectra of barrier oxide films on aluminum formed in inorganic electrolytes

In this paper, we have presented the results of the galvanoluminescence (GL) spectra measurement of barrier oxide films during aluminum anodization in inorganic electrolytes (aqueous solution of boric acid + borax, ammonium borate, etc.). We have used an ICCD based detection system for time-resolved spectral measurement of very weak light intensities in a wide range of wavelengths. For the first time we have showed that there are two peaks in the GL bands of barrier films. The first one is at about 430 nm, and the second shifts with anodization voltage from 600 nm to 680 nm. Comparison with GL spectra of porous oxide films in inorganic electrolytes indicates the same GL mechanism in barrier and porous oxide films.

The influence of aluminum treatment and anodizing conditions on the galvanoluminescence properties of porous oxide films formed in sulfuric acid solution

In this article, we have presented our recent investigation of luminescence originating from thin oxide film obtained by aluminum anodization in sulfuric acid solution. For the first time we have measured this weak galvanoluminescence (GL) and found strong influence of sample’s surface pretreatment as well as anodization conditions (current density, temperature of electrolyte and electrolyte concentration) on luminescence intensity. GL intensity is the highest for degreased samples, lower for chemically cleaned and almost disappears for electropolished samples. Results obtained in sulfuric acid confirmed the previous measurements in phosphoric and chromic acid that GL intensity is higher for higher current density, lower electrolyte temperature and lower electrolyte concentration.

Galvanoluminescence of porous oxide films formed by anodization of aluminum in chromic acid solution

In this paper, we have presented the results of the galvanoluminescence (GL) measurements of porous oxide films formed by anodization of aluminum in chromic acid aqueous solution. For the first time we have obtained GL spectra in this electrolyte in spite of strong light absorption in part of measuring spectral range, thank to improved experimental procedure, which included preliminary measurement of absorption spectra of the electrolyte. Two spectral peaks at about 425 and 595 nm were observed. Further investigation showed strong influence of surface pretreatment and anodic conditions (current density, temperature of electrolyte and electrolyte concentration) on GL intensity. The ratio of intensities of observed peaks is linear function of the temperature of electrolyte.

The influence of anodizing conditions on the galvanoluminescence spectra of porous oxide films on aluminum formed in phosphoric acid solution

The influence of current density, anodization voltage, electrolyte temperature and electrolyte concentration on the galvanoluminescence (GL) spectra of porous oxide layers obtained by aluminum anodization in phosphoric acid solution was investigated. We have measured GL spectra in both galvanostatic and potentiostatic steady-state regimes and observed two spectral peaks at 425 and 595 nm. It was established that the ratio of intensities of observed peaks does not depend directly on current density (in galvanostatic regime) and anodization voltage (in potentiostatic regime), but strongly depends on electrolyte temperature and electrolyte concentration. The obtained dependences are linear for both regimes.

The theory of galvanoluminescence in the anodic oxide films obtained by aluminum anodization in ammonium tartrate

The experimental as well as the theoretical aspects of galvanoluminescence (GL) during the anodization of aluminum in the barrier-layer forming electrolyte ammonium tartrate are considered in this paper. The experimental results are explained by the avalanche theory, where the electron trapping processes and the influence of interference effects on the measured GL intensity have been taken into account as well. It is assumed that the luminescence is produced by impact excitation of luminescent centers (LCs). The electric field strength F in the parts of the oxide film occupied by avalanches is calculated in addition to its influence on the ionization coefficient α, mean free path for electron capture by trap x 0 and the number of the avalanche electrons. The formula for spectral intensity of GL is also derived.

The galvanoluminescence spectra of porous oxide layers formed by aluminum anodization in oxalic acid

This paper presents the result of the most recent investigations of the galvanoluminescence (GL) spectra of porous oxide layers formed by aluminum anodization in oxalic acid. A new experimental procedure for GL spectra recording was established. This method can be easily applied to GL spectral measurements on porous anodic films. The spectra were recorded for different values of temperature and anodization current density. Two spectral peaks at 446 and 485 nm, respectively, were observed, indicating the probable existence of two kinds of luminescence centers incorporated in the oxide. In addition, it was discovered that the intensity ratio for the two peaks changes with the current density. Those GL measurements, with further photoluminescent (PL) measurements should lead to a definitive explanation of the GL phenomena, as well as of the nature and distribution of luminescent centers in both porous and barrier oxide films on aluminum.

Electroreflectance and Galvanoluminescence of GaAs

In electroreflectance (ER) using the semiconductor-electrolyte technique (saturated solution, 0.5 N, of NH4NO3 in ethyl alcohol at T ∼ 300 °K), a method of modulation of the surface barrier by single-sign square-wave pulses is proposed. This allows an estimation of the surface equilibrium electric fields. They are 5.6 × 104, 1.1 × 105, and 5.7 × 105 V/cm for n = 1.9 × 1014, 7.1 × 1015, and 3.4 × 1017 cm−3, respectively. The surface of these samples has an inversion layer. In samples with n and p = 1016 − 1018 cm−3, the E0 and E0 + Δ0 peaks are displaced 0.02–0.03 eV to smaller energies relative to E0 of the purest sample, n = 1.9 × 1014 cm−3, which has E0 = Eg = 1.43 eV. This shift might be explained by tailing and impurity banding. In samples with n≳1018 cm−3, ER spectra are distorted and seem to be caused by the Moss-Burstein shift modulation. During ER measurements, galvanoluminescence (GL) appears for both n- and p-type samples. Measurements of GL vs voltage and time were made. GL spectra were measured for some n-type samples which agree with photoluminescence and cathodoluminescence. Maximum emitted power of radiation is ∼ 30 μW with quantum efficiency ∼ 10−4. A hole injection mechanism from the electrolyte qualitatively explains the behavior. During ER measurements by the electrolyte method, it is shown that it is necessary to take into account the appearance of GL since this effect can lead to erroneous ER results.

Electrode glow during electrolysis - Galvanoluminescence

Electrode glow during electrolysis - Galvanoluminescence