L. Bryja

Enhancement of Green Terbium-Related Photoluminescence from Highly Doped Microporous Alumina Xerogels in Mesoporous Anodic Alumina

Strong enhancement of green photoluminescence (PL) from microporous alumina xerogels, highly doped with terbium (from 30 to 60 wt % as Tb 2 O 3 ), is reported. The regular structure of a 30 μm thick, mesoporous anodic alumina layer was exploited for spin-on deposition of the alumina xerogel in a single step. The green PL, associated with predominant 5 D 4 - 7 F 5 transitions, along with 5 D 4 7 F j , j = 3, 4, 5, 6 transitions of Tb 3+ , was found to increase with terbium concentration in the alumina xerogel. This effect is attributed to cross-relaxation. The thermal quenching of the green terbium-related emission does not exceed a factor of two within a temperature range from 10 to 300 K for any of the alumina xerogels confined in anodic alumina. Further, such quenching is much reduced with the rise of temperature compared with (i) Tb-doped titania xerogel, (ii) Tb-implanted thermally grown silicon dioxide film, and (iii) Tb-doped alumina xerogels fabricated onto monocrystalline silicon Thus, the terbium-doped structure comprising alumina xerogel/anodic alumina is proposed as a basis for green room-temperature luminescent images.

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.

MOVPE GaN Grown on Alternative Substrates

The structure, morphology and optical properties of GaN films deposited by metalorganic vapour phase epitaxy (MOVPE) on alternative substrates: ZnO, NdGaO, YSZ (yttria stabilized zirconia). Scanning electron microscopy, X-ray diffraction and photoluminescence were used for the epitaxial layers characterisation. The obtained results have been compared to those of GaN layers grown on c-plane sapphire substrates. It was established that the most important step towards the realisation of device quality GaN material on alternative substrates is the first stage of the growth process.

Photoluminescence investigations of 2D hole Landau levels in p-type single Al_{x}Ga_{1-x}As/GaAs heterostructures

We study the energy structure of two-dimensional holes in p-type single Al 1 - x Ga x As/GaAs heterojunctions under a perpendicular magnetic field. Photoluminescence measunnents with low densities of excitation power revealrich spectra containing both free and bound-carrier transitions. The experimental results are compared with energies of valence-subband Landau levels calculated using a numerical procedure and good agreement is achieved. Additional lines observed in the energy range of free-carrier recombinations are attributed to excitonic transitions. We also consider the role of many-body effects in photoluminescence spectra.

Magneto-optical probing of weak disorder in a two-dimensional hole gas

In two-beam magneto-photoluminescence spectra of a two-dimensional valence hole gas we identify the three-level energy spectrum of a free positive trion with a field-induced singlet-triplet transition. The recombination spectrum of acceptor-bound trions is also detected, including a cyclotron replica corresponding to the hole shake-up process. The emergence of a shake-up peak at low temperature is shown to be a sensitive probe of the presence of a small number of impurities inside the high-mobility quantum well, and its relative position is directly related to the hole cyclotron mass.

Optical properties of Zn3P2 thin films

Abstract Polycrystalline and amorphous thin films of Zn 3 P 2 were deposited on SiO 2 and A1 2 O 3 oriented crystal substrates by direct evaporation from a quartz crucible at temperatures of 820–970 K. The thickness of the layers varied from 0.16 to μm. Structural studies by the X-ray diffraction method indicated good quality of the samples. Transmission and reflection measurements were carried out in the wide energy range 1–5 eV. The absorption coefficient and reflectivity spectra, taking into account strong light interference, were calculated. In transmission measurements, optical transitions in the Γ points (1.5 eV) as well as in the L points (2.7 eV) of the Brillouin zone were observed: in reflection measurements, transitions in the L and X (4.6 eV) points were observed. The those for monocrystals.

Impurity-related emission in the photoluminescence from p-type modulation doped Al1−xGaxAs/GaAs heterostructures

Abstract We investigated low-temperature photoluminescence from p-type Al1−xGaxAs/GaAs heterostructures. Our measurements show that at low laser power the H-band emission disappears and is replaced by a line resulting from the recombination of donor-bound electrons with two-dimensional holes. The properties of both lines are explained based on the results of detailed band structure calculations. Measurements in magnetic fields enabled us to examine the binding energy of donor in parallel electric and magnetic fields.

Structure of Oxygen - Implanted Silicon Single Crystals Treated at ≥1400 K under High Argon Pressure

The structure of oxygen - implanted (up to a dose 6x10 17 cm -2 ) silicon, Si:O, treated at 1400 - 1550 K under high (up to 1.5 GPa) argon pressure, was investigated by numerous methods. The oxygen distribution peak narrowed, the dimensions of extended defects decreased and the peak intensity in the Si - O - Si asymmetric stretching vibrational mode diminished with pressure. That effects are explained by decreased misfit at the SiO 2-x /Si boundary and more numerous nucleation sites created in Si:O treated at high pressure.