Annual Report 2012 - Latvijas Universitātes Cietvielu fizikas institūts

Main investigations and results
ALUMINUM OXYDE Al 2 O 3
L.Trinkler, B.Berzina
Photoluminescence studies were fulfilled for nominally pure Al 2 O 3 nanopowder
samples with different grain size and different lattice structure phases synthesized in
RTU Institute of Inorganic Chemistry. It was found that luminescent properties of this
material are determined primarily by a phase of crystal lattice and uncontrolled
impurities, which are present in very small concentrations. Phase transition from δ to α
structure is followed with drastic changes in luminescence spectra – wide diffuse bands
in 600-900 nm range are replaced by narrow lines. This phenomenon is explained by
switching of active luminescence centers due to transformation of crystal field symmetry
as a result of phase transition. It was found that wide diffuse luminescence bands typical
for samples with δ phase occur due to emission titanium, iron and chromium ions (at
750 nm, 700-900 nm and 690-710 nm, correspondingly), while narrow lines in
photoluminescence of samples with α phase arise due to emission of chromium and
manganese ions. The results obtained allow evaluate the Al 2 O 3 being useful for red light
emitters.
These studies were performed within a support of European project ERDF
2010/0253/2DP / 2.1.1.1.0/10/APIA/VIAA/079.
HEXAGONAL BORON NITRIDE hBN
V.Korsak, B. Berzina, L.Trinkler
Spectral characterization of hBN consisting of macro-size grains or nanotubes was
performed. Photoluminescence spectra of materials were studied within a wide
temperature range between 8 K and 300 K [1]. It was found that in all materials studied
there are two main phonon-assisted luminescence bands at ~300 nm and ~400 nm
caused by native defects of hBN appearing independently on a particle size and material
origin. The 300 nm luminescence is related to the intracenter processes of a single
defect, characterized with the phonon-assisted luminescence/exitation spectra presenting
a common zero-phonon line (Fig.4). It was found that the 400 nm luminescence is
caused by recombination of a donor-acceptor pair, which is located at or near material
surface. It was also found that the intensity of the 400 nm luminescence in hBN depends
on oxygen content in ambient atmosphere surrounding the sample. This feature allows
propose hBN as a material applicable for oxygen sensors.
On basis of investigations mentioned above Valdis Korsaks has defended his PhD
Thesis.
These studies were performed within a support of European project ERDF
2010/0253/2DP / 2.1.1.1.0/10/APIA/VIAA/079.
ALUMINUM NITRIDE AlN
L.Trinkler, B. Berzina, V.Korsaks, R.Kirsteins
The native defect-induced photoluminescence of AlN of different structures
(ceramics, macro-size powder, nanopowder, nanorods, nanotips) was studied using the
spectral methods mentioned above. It was found that there are two main luminescence
bands at ~400 nm (UV band) and 480 nm (blue band), which are observable in all AlN
structures with varied ratio of their intensities. It allows conclusion that the same defect
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