Journal
RSC ADVANCES
Volume 7, Issue 60, Pages 37643-37653Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c7ra05074g
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Funding
- Executive Unit for Financing Higher Education, Research, Development and Innovation of the Romanian Ministry of Education and Scientific Research [PN-III-P2-2.1-PED-2016-1043]
- Spanish Ministry of Economy and Competitiveness [ENE2014-56109-C3-3-R]
- Spanish Ministry of Economy and Competitiveness, through the Severo Ochoa Programme for Centres of Excellence in RD [SEV-2015-0496]
- Consejo Superior de Investigaciones Cientificas [JAE-Pre-201100578, JAE-Pre-083]
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Photoactive europium doped titanium dioxide (Eu: TiO2) thin films were grown by a matrix assisted pulsed laser evaporation technique. TiO2 and Eu cation-adsorbed TiO2 nanoparticles (NPs) sols were used as starting materials. The sols were synthesized by a colloidal sol-gel route. In order to obtain solid targets, the sols were cooled down until solidification in liquid nitrogen. The irradiation of the solid targets was performed in a controlled oxygen atmosphere using an UV KrF* (lambda = 248 nm, tau(FWHM) nu 25 ns, n = 10 Hz) excimer laser source. The NPs were transferred and deposited onto solid substrates placed in the front of the frozen targets, forming continuous thin films. The as-grown undoped and Eu: TiO2 thin films were submitted to post-deposition thermal treatments. The surface morphology, crystalline structure, and chemical composition of the thin films were characterized by field emission scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Functional optical properties of the films were investigated by UV-VIS-NIR spectroscopy, spectroscopic ellipsometry, and photoluminescence as a function of dopant concentration in the TiO2 host and annealing temperature. A direct correlation was established between the processing conditions, films structure, chemical composition and oxidation states studied both at the top surface and in-depth as well as their functional, optical properties. Eu doping induces a blue-shift of the absorption edge with respect to the as-grown samples. Under visible light excitation (lambda = 488 nm, emitted by an Ar+ laser source), the Eu: TiO2 samples show characteristic photoluminescence corresponding to the D-5(0) -> F-7(i) (i = 0, 1, 2, 3, 4) transitions of Eu+ ions in the visible spectral range. The samples treated at the highest annealing temperature are characterized by strong photoluminescence emission, high transmittance in the VIS-NIR spectral regions, and high refractive index.
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