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Photoluminescence emission of nanoporous anodic aluminum oxide films prepared in phosphoric acid.

Nourmohammadi A, Asadabadi SJ, Yousefi MH, Ghasemzadeh M - Nanoscale Res Lett (2012)

Bottom Line: The photoluminescence emission of nanoporous anodic aluminum oxide films formed in phosphoric acid is studied in order to explore their defect-based subband electronic structure.Different excitation wavelengths are used to identify most of the details of the subband states.Gaussian analysis of the emission data indicates that subband states change with anodizing parameters, and various point defects can be formed both in the bulk and on the surface of these nanoporous layers during anodizing.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, Faculty of Science, University of Isfahan, Isfahan, 81746-73441, Iran. a.nourmohammadi@phys.ui.ac.ir.

ABSTRACT
The photoluminescence emission of nanoporous anodic aluminum oxide films formed in phosphoric acid is studied in order to explore their defect-based subband electronic structure. Different excitation wavelengths are used to identify most of the details of the subband states. The films are produced under different anodizing conditions to optimize their emission in the visible range. Scanning electron microscopy investigations confirm pore formation in the produced layers. Gaussian analysis of the emission data indicates that subband states change with anodizing parameters, and various point defects can be formed both in the bulk and on the surface of these nanoporous layers during anodizing.

No MeSH data available.


Related in: MedlinePlus

Dependence of the PL emission spectra to the anodizing time.
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Figure 4: Dependence of the PL emission spectra to the anodizing time.

Mentions: Most of the previous reports have related the PL properties of PAAO layers to the optical transitions within individual oxygen vacancies. However, there is a clear-cut distinction between their interpretations on the type of the oxygen vacancies. Some researches claim in their articles that the PL spectra are concerned to the singly ionized oxygen vacancies [12,13,15]. But others relate the spectra to both singly ionized and neural oxygen vacancies [11,14]. Singly ionized oxygen vacancies are generally called F+ centers. These point defects form when an electron is trapped in a double ionized oxygen vacancy. Neutral oxygen vacancies are often called F centers. They can be formed if two electrons are trapped in a double ionized oxygen vacancy. Our results could not confirm the interpretations of the first group; otherwise, our results would not agree with the results on crystalline Al2O3. According to Lee and Crawford studies on sapphire [19] and Evans and coworkers on crystalline α-Al2O3[20], if crystalline Al2O3 is excited under a 4.8 eV (260 nm) wavelength, it would emit UV PL radiation due to the F+ color centers at approximately 3.8 eV (326 nm). Only one PL emission about 3.8 eV is fitted out among our results (see the 323-nm peak in Figure 4c). But several visible emissions far greater than 323 nm are identified (Figure 3a). As it is discussed in the next section, our results correspond better with the interpretations of some of the second group of researchers who suggest that F+ centers exist in the bulk structure of PAAO membranes, and neural oxygen vacancies, F centers, are on their surface [11]. Chen and coworkers [21] report measurement of a blue PL emission approximately 420 nm in sapphire due to F+ color centers using a 244-nm excitation wavelength. This excitation is close to the optimized excitation wavelength identified in our study, 265 nm, and several emissions around 420 nm are fitted out in our analyzed PL data (see Figure 3a,b,c). It is shown in the next section that most of these emissions originate from bulk of the nanoporous layer, and emissions which are far greater than 323 nm are from the layer surface.


Photoluminescence emission of nanoporous anodic aluminum oxide films prepared in phosphoric acid.

Nourmohammadi A, Asadabadi SJ, Yousefi MH, Ghasemzadeh M - Nanoscale Res Lett (2012)

Dependence of the PL emission spectra to the anodizing time.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3585920&req=5

Figure 4: Dependence of the PL emission spectra to the anodizing time.
Mentions: Most of the previous reports have related the PL properties of PAAO layers to the optical transitions within individual oxygen vacancies. However, there is a clear-cut distinction between their interpretations on the type of the oxygen vacancies. Some researches claim in their articles that the PL spectra are concerned to the singly ionized oxygen vacancies [12,13,15]. But others relate the spectra to both singly ionized and neural oxygen vacancies [11,14]. Singly ionized oxygen vacancies are generally called F+ centers. These point defects form when an electron is trapped in a double ionized oxygen vacancy. Neutral oxygen vacancies are often called F centers. They can be formed if two electrons are trapped in a double ionized oxygen vacancy. Our results could not confirm the interpretations of the first group; otherwise, our results would not agree with the results on crystalline Al2O3. According to Lee and Crawford studies on sapphire [19] and Evans and coworkers on crystalline α-Al2O3[20], if crystalline Al2O3 is excited under a 4.8 eV (260 nm) wavelength, it would emit UV PL radiation due to the F+ color centers at approximately 3.8 eV (326 nm). Only one PL emission about 3.8 eV is fitted out among our results (see the 323-nm peak in Figure 4c). But several visible emissions far greater than 323 nm are identified (Figure 3a). As it is discussed in the next section, our results correspond better with the interpretations of some of the second group of researchers who suggest that F+ centers exist in the bulk structure of PAAO membranes, and neural oxygen vacancies, F centers, are on their surface [11]. Chen and coworkers [21] report measurement of a blue PL emission approximately 420 nm in sapphire due to F+ color centers using a 244-nm excitation wavelength. This excitation is close to the optimized excitation wavelength identified in our study, 265 nm, and several emissions around 420 nm are fitted out in our analyzed PL data (see Figure 3a,b,c). It is shown in the next section that most of these emissions originate from bulk of the nanoporous layer, and emissions which are far greater than 323 nm are from the layer surface.

Bottom Line: The photoluminescence emission of nanoporous anodic aluminum oxide films formed in phosphoric acid is studied in order to explore their defect-based subband electronic structure.Different excitation wavelengths are used to identify most of the details of the subband states.Gaussian analysis of the emission data indicates that subband states change with anodizing parameters, and various point defects can be formed both in the bulk and on the surface of these nanoporous layers during anodizing.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, Faculty of Science, University of Isfahan, Isfahan, 81746-73441, Iran. a.nourmohammadi@phys.ui.ac.ir.

ABSTRACT
The photoluminescence emission of nanoporous anodic aluminum oxide films formed in phosphoric acid is studied in order to explore their defect-based subband electronic structure. Different excitation wavelengths are used to identify most of the details of the subband states. The films are produced under different anodizing conditions to optimize their emission in the visible range. Scanning electron microscopy investigations confirm pore formation in the produced layers. Gaussian analysis of the emission data indicates that subband states change with anodizing parameters, and various point defects can be formed both in the bulk and on the surface of these nanoporous layers during anodizing.

No MeSH data available.


Related in: MedlinePlus