20 research outputs found
Anatase-to-rutile phase transition of samarium-doped TiO2 powder detected via the luminescence of Sm3+
AbstractWe employed a sol-gel route to prepare 1% samarium-doped TiO2 nanopowders. Time-resolved photoluminescence (PL) and Raman characterization was performed. After a thermal treatment the powder crystallized in an anatase phase and revealed intense Sm3+ photoluminescence. The emission spectrum of Sm3+ exposed well-resolved crystal-field splitting enabling monitoring of the changes in the local environment.We thoroughly investigated the influence of the annealing treatment (in air) on Sm emission intensity. Annealing up to 800 ∘C led to a systematic enhancement of Sm emission. Annealing at higher temperatures, however, led to a marked weakening of Sm3+ emission and simultaneous appearance of an emission band near 830 nm. Annealing temperatures as high as 1000 ∘C were needed to induce the phase transition from anatase to rutile. It was possible to use Sm3+ as a structural probe revealinge peculiarities of the phase transition
Elaboration of IVB group metal oxide structures and their possible applications
Elaboration of IVB group metal oxide structures and their possible
applications
Summary
The description and discussion about an easy and flexible method for
preparing of nanometer level homogeneous Ti(OBu)4 Zr(OBu)4, Hf(OBu)4 based
sols and concentrates, suitable as precursors for preparing metal oxide thin (RE
doped and undoped) films and tubular microstructures were presented in the
current thesis.
The main results presented in current thesis can be summarized as follows:
• We have shown that spry pyrolysis, dip-coating and spin-coating techniques
can be used to prepare rare earths activated TiO2, ZrO2 and HfO2 films with
controllable and uniform thickness.
• We have demonstrated that metal alkoxide based synthesis of thin Sm3+
doped titania and hafnia films will yield materials which after band-to-band
optical excitation give Sm3+-specific emission with a well-resolved fine
structure. The latter indicates that the samarium ions are fitted in to quite
regular positions in the host lattices.
• We suggest the possibility of using synthesized RE doped HfO2 as
scintillator material (e.g. in medicine) as it has high density and atomic
number combined with luminescent properties for that application. Also we
propose that thin porous TiO2:Sm3+ films can be considered as
photoluminescence-based oxygen sensing material as intensity of the Sm3+-
specific emission was found to be sensitive to the chemical composition of
the ambient atmosphere.
• We have demonstrated for the first time that gelation of the surface of a
metal-alkoxide precursor, spontaneous cracking of obtained gel film,
subsequent dissolving the non-gelled layer of precursor will lead to selfrolling
of gel film segments. Obtained metal oxide micro-tubes are
transparent in visible light and have outer diameter of 20-30 μm. We have
also shown that obtained tubular gel structures can be baked at up to 500 oC
to crystalline the material. We propose that obtained oxide materials can be
used in the production of catalysts, gas-sensors, stationary phases in
chromatography, composite materials, MEMS or NEMS components, heat
insulators etc. Patent pending.
Summry in Estonian
IVB grupi metallide oksiidstruktuuride väljatöötamine ja nende võimalikud
rakendused
Käesolevas väitekirjas käsitletakse dopeerimatta ja haruldaste
muldmetallide ioonidega dopeeritud õhukeste oksiidkilede ja torukujuliste
mikrostruktuuride valmistamismeetodeid ja sünteesitud materjalide mõningaid
omadusi. Materjalide valmistamisel kasutatakse lähtematerjalidena metallide (Ti,
Zr, Hf) alkoksiidide ja nendest sünteesitud homogeenseid soole ja kontsentraate.
Tööst lähtuvad tulemused on järgmised:
• Näidati, et pihustus-pürolüüsi-, vurr-katmis- ja sukelduspindamistehnikat,
kasutades on võimalik valmistada kontrollitava ja ühtlase paksusega ja
haruldaste muldmetallide ioonidega dopeeritud õhukesi TiO2, ZrO2 and HfO2
kilesid.
• Näidati, et metallide alkoksiididel baseeruv Sm3+ dopeeritud titaan-, ja
hafniumoksiidkilede süntees annab materjali, mis tsoon-tsoon ergastuse
tulemusel kiirgab samaariumi 3+ ioonile iseloomuliku hästi eristatava
struktuuriga spektriga. Viimane näitab, et samaariumi ioonid on asetunud
regulaarselt põhioksiidi kristallvõresse.
• Pakume välja võimaluse, et sünteesitud haruldaste muldmetalli ioonidega
lisandatud HfO2 on potentsiaalselt rakendatav sintillaatormaterjalina, sest
sellises materjalis on ühendatud vastava rakenduse jaoks olulised omadused
nagu raske aatom, suur tihedus ja luminestsentskiirguse eraldumine kõrge
energiaga osakesega vastasmõjust. Samuti pakume välja, et Sm3+ ioonidega
dopeeritud TiO2 on rakendatav fotoluminestsensil põhineva hapniku sensori
väljatöötamiseks, sest täheldati, et sünteesitud materjalist lähtuv
luminestsentskiirguse intensiivsus on tundlik ümbritseva atmosfääri
keemilisele koostisele.
• Näidati esmakordselt, et metallalkoksiidi kontsentreeritud sooli pinna
geelistamisel ja selle spontaanse pragunemise tulemusena saadud geelkile
fragmentide geelistumatta materjali lahustamine viib geel-segmentide
rullumiseni. Saadud metalloksiid mikro-torud on nähtavas valguses
läbipaistvad ja omavad välisdiameetrit 20-30 μm. Samuti näitasime, et
saadud struktuure on võimalik kuumutada vähemalt 500 oC, mis on vajalik
materjali viimiseks oksiidsele keemilisele koostisele. Sünteesitud materjalide
võimalikeks rakendusteks näeme nende kasutamist näiteks katalüsaatorite,
gaasisensorite, kromotograafia kolonnide seisvate faaside,
komposiitmaterjalide, mikro- või nanoelektromehaaniliste süsteemide
(MEMS või NEMS) komponentide, soojusisolatsioonimaterjalide
valmistamiseks. Väljatöötatud meetodi tehniline lahendus on patenteeritud
Simulation of cracking of metal alkoxide gel film formed on viscous precursor layer using a spring-block model
Drying-induced cracking of thin films attached to a non-solid (viscous) substrate is studied both experimentally and numerically. The numerical model is essentially a modification of the spring-block model, introducing a shear stress due to faster drying of the upper film layer, and annealed disorder in the distribution of the spring strengths. The simulation results are in a qualitative agreement with the experimental results, covering all the qualitatively different experimental regimes of the fragment formation. The model allows us to identify the physical processes responsible for the formation of micro-tubes in our experiments, and is helpful in designing and interpreting the film cracking experiments