N. V. Gaponenko

Visible luminescence from europium-doped alumina sol–gel-derived films confined in porous anodic alumina

Abstract In this work, we report on strong photoluminescence (PL) of europium-doped alumina sol–gel-derived films fabricated onto porous anodic alumina of 30 μm thickness. The PL spectra represent a set of peaks typical for Eu 3+ ions with the maximum at 617 nm. PL intensity was found to increase with increase of Eu content in xerogel. Cooling the samples from 300 to 10 K leads to an increase in PL intensity. Eu PL increases nearly linearly with the excitation power within a range up to 25 mW/cm 2 . Red Eu-related PL from all of the samples is visible to the naked eye even at room temperature.

Comparison of terbium photoluminescence from ion implanted and sol–gel-derived films

Abstract In this work, we investigate the photoluminescence (PL) of terbium-doped films fabricated by ion implantation and sol–gel synthesis. Terbium implantation was carried out into SiO 2 , ZrO 2 and Al 2 O 3 thin film fabricated by dry processes onto silicon substrates followed by heat treatment in vacuum at a temperature ranging from 473 to 873 K during 30 min. Sol–gel-derived films were fabricated onto monocrystalline silicon or porous anodic alumina substrates by spin-on deposition of titania or alumina-based sol containing aqueous-alcohol solution of terbium nitrate. PL measurements were carried out at temperatures from 10 to 300 K. Comparison of PL data obtained from Tb-implanted SiO 2 , ZrO 2 and Al 2 O 3 films allows the conclusion that ZrO 2 is the best host material for Tb 3+ ions, revealing a set of sharp well resolved bands corresponding to 5 D 4 – 7 F J electron transitions of Tb 3+ ions with the maximum at 546 nm. Tb PL was found to be 15–20 times stronger for xerogels fabricated onto porous anodic alumina 30-μm-thick in comparison with ion implanted thin films.

Photoluminescence investigation of porous anodic alumina with spin-on europium-containing titania sol–gel films

Abstract In this work, we investigate europium-containing sol–gel derived films fabricated onto porous anodic alumina (PAA) of thickness ranging from 0.5 to 5 μm. The sols were prepared from Ti(OC 2 H 5 ) 4 precursor mixed with aqueous-alcohol solution of europium nitrate and deposited onto PAA. The concentration of europium oxide in xerogel was 40 wt.%. The PL spectra exhibit bands typical for Eu 3+ corresponding to 5 D 0 → 7 F j ( j =1–4) electron transitions with the maximum at 617 nm ( 5 D 0 → 7 F 2 ). The PL intensity of all the bands increases with the thickness of PAA. The samples exhibit a red light emission visible to the naked eye within the investigated temperature range from 10 to 300 K.

High‐efficiency luminescent sources fabricated in mesoporous anodic alumina by sol‐gel synthesis

This paper summarizes our recent results on the synthesis and investigation of photoluminescence (PL) from lanthanide-doped microporous xerogel solids mesoscopically confined in porous anodic alumina (PAA). It was demonstrated, for Tb-doped samples, that the PL intensity is strongly enhanced in comparison to thin xerogel films processed onto flat surfaces and increased with the thickness of the PAA layer. It was revealed for both Tb- and Eu-doped PAA-based structures that maximum emission is achieved at a excitation wavelength near 285 nm for the employed TiO 2 and Al 2 O 3 xerogels. Strong Eu- and Tb-related PL visible to the naked eye was demonstrated, and a method for the fabrication of luminescent images based on anodizing, photolithography, and sol-gel processes is proposed.

Inhomogeneous nanostructured honeycomb optical media for enhanced cathodo- and under-x-ray luminescence

Photo-, radio-, and pulse cathodoluminescence spectra from sol-gel derived titania, doped with strontium and terbium, deposited on porous anodic alumina (PAA) films are reported. The morphology and qualitative elemental depth distributions have been examined by transmission electron microscopy, scanning electron microscopy, and radio-frequency glow discharge optical emission spectroscopy. PAA films with pore and cell sizes ranging from 170 to 190 and 240 to 270 nm, respectively, have been generated on aluminum and monocrystalline silicon substrates followed by spin-on sol-gel derived coating with the subsequent thermal treatment. The resultant PAA surface is not coated with a continuous xerogel film; the xerogel is mainly distributed near the pore bases, leaving much of the pore volume unfilled. The xerogel/PAA structures reveal terbium-related luminescence under x-ray excitation and cathodoluminescence. The same xerogels generated on monocrystalline silicon revealed no cathode- or under-x-ray luminescenc...

Luminescence of Eu3+ and Tb3+ Ions in the Structure Microporous Xerogel/Mesoporous Anodic Aluminum Oxide

We have investigated the luminescence, luminescence excitation, and transmittance of europium- and terbium-doped xerogel films formed on smooth, nanotextured surfaces and in the pores of anodic aluminum oxide. Some factors responsible for enhancement of luminescence in the structure lanthanide-doped xerogel/mesoporous anodic aluminum oxide have been analyzed. It is assumed that the optical excitation of lanthanide ions can be realized directly, through a xerogel matrix, and due to the multiple scattering of exciting radiation by the matrix of mesoporous anodic aluminum oxide.

Enhanced Luminescence of Europium in Porous Anodic Alumina Films

Xerogels doped with lanthanides embedded in mesoporous matrices are known to exhibit intensive lanthanides-related photoluminescence (PL). In this paper we report on novel features peculiar to porous anodic alumina and Eu-doped xerogels embedded therein. For Eu-doped titania xerogel fabricated in a single spin-on step Eu PL increases with the thickness of porous anodic alumina ranging from 0.5 to 5 μm. The structure Eu-doped titania xerogel/porous anodic alumina reveal anisotropy of luminescence at 617 nm (5D0 → 7F2 transitions of Eu3+) with a pronounced maximum towards the channels of the anodic alumina pores. Furthermore, a membrane of porous anodic alumina reveals strong anisotropy of light scattering. Development of these anisotropic properties for the purpose of further PL enhancement of optically active inclusions incorporated in mesoscopic channels of anodic alumina is discussed.

Ion?ion interaction in two-dimensional nanoporous alumina filled with cubic YAlO3?:?Tb3+ matrix

Terbium doped YAlO3 composites, with terbium concentrations up to 2.11 at%, were fabricated by co-precipitation in porous anodic alumina films grown on silicon. The presence of the cubic YAlO3 phase was confirmed by x-ray diffraction and FT-IR analysis. The fabricated samples demonstrate photoluminescence (PL) within the range 350?640?nm, which is associated with f?f transitions from the 5D3, 5G6 and 5D4 levels of Tb3+ ion. Additionally, a broad and fast- decaying PL band in the blue range has been observed, which is associated with defect states. Based on PL excitation spectra, the main excitation channel of Tb3+ ions is due to 4f?5d transitions. Excitation bands observed at 235, 270 and 320?nm have been related to the permitted low-spin 5d2 [LS], 5d1 [LS] and forbidden high-spin 5d1 [HS] states, respectively. The PL decay spectra have been measured, with the results analysed using the maximum entropy method; a strong indication of ion?ion interaction has been observed. The distribution of Tb3+ ions in the PAA?:?YAlO3 structure has been proposed and its influence on optical properties of Tb3+ ions has been discussed.

Terbium photoluminescence in yttrium aluminum garnet xerogels

Based on a colloidal solution containing terbium, yttrium, and aluminum metal ions, a powder was synthesized and films of terbium-doped yttrium aluminum garnet Tb0.15Y2.85Al5O12 were grown on single-crystal silicon and porous anodic alumina. Annealing of the sample in a temperature range from 200–1100°C results in an increase in the photoluminescence intensity in the wavelength range from 480–640 nm, which is caused by Tb3+ ion intra-atomic transitions 5D4→7Fj (j = 3, 4, 5, 6). Annealing at 900°C and higher temperatures gives rise to low-intensity photoluminescence bands in the region of 667 and 681 nm, which correspond to transitions 5D4→7F0, 5D4→7F1, and room-temperature Stark term splitting, which suggests the existence of a crystalline environment of Tb3+ ions. The FWHM of spectral lines in the region of 543 nm decreases from ∼10 to ∼(2–3) nm as the xerogel annealing temperature is increased from 700 to 900°C and higher. Three bands with maxima at 280, 330, and 376 nm, which correspond to Tb3+ ion transitions 7F6→5I8, 5L6, 5G6, 5D3, are observed in the photoluminescence excitation spectra of the studied structures for the emission wavelength at 543 nm. X-ray diffraction detected the formation of a crystalline phase for a terbium-doped yttrium aluminum garnet powder after annealing at 1100°C.

Synthesis and Photoluminescence of Lanthanide-Doped Xerogels in Mesoporous Matrix

The method of synthesis of the mesoscopic structures xerogel/porous anodic alumina (PAA), xerogel/opal, doped with erbium and other optically active lanthanides and their optical properties are considered