B.R. Jovanić

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.

Investigation of anodic alumina by a photoluminescence method: II

Abstract Photoluminescence emission spectra of anodic oxide films on aluminium were measured under the conditions where an interference of the Lummer-Gehrke type takes place (the emission angle was approximately equal to the total reflection angle). Both barrier (obtained in 0.1 M ammonium tartrate) and porous (obtained in 0.1 M oxalic acid) oxide films were investigated. From the positions of sharp interference maxima and minima in the emission spectra, a very precise determination of film thickness d and anodization rate ϰ is possible. The ϰ values obtained (ϰ1 = 1.33 nm V-1 in ammonium tartrate; ϰ2 = 0.317 nm min-1 in oxalic acid) are in excellent agreement with the results of other workers and with our previous results obtained by other luminescence methods. This procedure is more precise than the photoluminescence method described previously and it does not need any assumption about the spatial distribution of photoluminescence centres.

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

Abstract 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 x0 and the number of the avalanche electrons. The formula for spectral intensity of GL is also derived.

Effect of hydrostatic pressure on fluorescence lifetime for 0-0 line (5D0 → 7F0 transition) in SrFCl : Sm2+

Abstract The lifetime τ of fluorescence 0-0 line, 5 D 0 → 7 F 0 , in SrFCl:Sm 2+ has been measured under high pressure up 10 GPa. This study shows that τ decreases exponentially with pressure and can be expressed by exponential regression τ (s) = 0.1853 + 1.1923 exp(−0.1366P) (GPa).

Determination of the refractive index of porous anodic oxide films on aluminium by a photoluminescence method

It is shown that previously described photoluminescence (PL) methods can be used for simultaneous determination of the refractive index n and thickness d of porous anodic oxide films formed on aluminium. The measurement of n and d is based on the determination of the positions of interference maxima which appear in emission PL spectra. For anodic alumina formed in 0.1M oxalic acid at T = 25 ± 1 °C and j = 2.5–12.5 mA cm-2 we obtained n = 1.68 ± 0.02 in agreement with the result of Huber and Gaugler (1.65±0.02) obtained by another measurement method.

The effect of pressure on the position and fluorescence lifetime for the transition in

The aim of this study was to assess the effect of pressure on the position and fluorescence lifetime for the transition in within the 0 - 104 kbar range. The relationship between the pressure and the line position is given by linear regression: (kbar). The change of the fluorescence lifetime for the transition with pressure can be expressed by an exponential decay: .

Investigation of the porosity of thin Anodic Al2O3 films by interference of photoluminescence radiation

Abstract Photoluminescence emission spectra of thin (1–5 μm thick) Al 2 O 3 films formed by d.c. anodization of pure aluminium in 0.1 M oxalic acid have been investigated under the conditions of Lummer-Gehrke-type interference (in which the emmission angle is approximately equal to the total reflection angle). In this case, both p and s components of polarized light give additional (doublet) interference maxima owing to the inhomogeneity (porous structure) of the films. From the position of these doublets it is possible to determine the porosity coefficients of oxide films. The results are in good agreement with data obtained by electron microscopy.

High pressure and lifetime of the 2E level in ruby

The influence of high pressure (0-200 kbar) on the lifetime τ of 2E metastable level of Cr3+ ion ruby is considered. The essentials of the pressure dependence of τ can be understood by assuming a change of oscillator strength, coordination number and effective charge of the Cr3+ ion under pressure. On the basis of these concepts the calculated results for τ are found in good agreement with experimental data up to 120 kbar.

Effect of pressure on the ruby fluorescence lifetime

Abstract The pressure dependence of the fluorescence lifetime of ruby has been measured in the 0–118 kbar pressure range. A linear increase of emission lifetime τ is found with a slope Δτ/Δ P =0.0312 ms/kbar (for the RI line). This increase can be correlated with the pressure dependence of the crystal field strength.

Theoretical consideration of the pressure induced changing of fluorescence lifetime for Sm2+ 0-0 line (5D0 → 7F0 transition) in SrFCl

Abstract The effect of high pressure on the lifetime τ of fluorescence 0-0 line, 5 D 0 → 7 F 0 , in SrFCl : Sm2+ was theoretically considered up to 100 Kbar. The simple model describes the effect of pressure on τ. The starting points were the assumptions that the high pressure can cause the change of τ through a great influence on the energy of 5 D 0 → 7 F 0 transition, refractive index of crystal n and greatest inter-ionic separation R between the Sm2+ ion and surrounding ligand (Cl−). Calculated pressure-induced change of lifetime τ is in good agreement with the experimental data.