Abstract
Monoclinic Bi2O3:Ho3+ powder was synthesized using a co-precipitation method, followed by the deposition of Bi2O3:Ho3+ thin films on Si (100) substrates at various substrate temperatures (room temperature–600 °C) and oxygen partial pressures (5–200 mT) using pulsed-laser deposition. X-ray diffraction analysis showed a single α-Bi2O3 phase at temperatures of 400 and 500 °C, while a mixed α- and β-Bi2O3 phase was obtained at 600 °C. The films deposited at the different oxygen partial pressures showed an α-Bi2O3 and non-stoichiometric phase. The influences of different substrate temperatures and oxygen partial pressures on the morphology and the thickness of the films were analyzed using a scanning electron microscope. The root mean square roughnesses of the films were determined by using an atomic force microscope. The surface components, oxidation states and oxygen vacancies in all the deposited thin films were identified by X-ray photoelectron spectroscopy. The optical band gap of the Bi2O3:Ho3+ thin films was calculated using diffused reflectance spectra and was found to vary between 2.89 and 2.18 eV for the deposited films at the different temperatures, whereas the different oxygen partial pressures showed a band gap variation between 2.97 and 2.47 eV. Photoluminescence revealed that Ho3+ was the emitting centre in the isolated thin films with the 5F4/5S2 → 5I8 transition as the most intense emission in the green region.
Highlights
The recent popularity of Bi2 O3 as a p-type semiconductor as a research topic, is mainly due to its attractive physical properties, which include wide optical bandgap energies that range from about2.0 to 3.9 eV, high dielectric permittivity, good photocatalytic activity, high refractive index, oxide ion conductivity and good photoluminescence (PL) [1,2]
In our pervious study we reported on the structural, optical, photoluminescence and photocatalytic properties of the monoclinic
The disks were introduced into a pulsed laser deposition (PLD) chamber and placed in a target holder which was rotated at 10 degrees/min to avoid laser-pinning
Summary
The recent popularity of Bi2 O3 as a p-type semiconductor as a research topic, is mainly due to its attractive physical properties, which include wide optical bandgap energies that range from about2.0 to 3.9 eV, high dielectric permittivity, good photocatalytic activity, high refractive index, oxide ion conductivity and good photoluminescence (PL) [1,2]. Bi2 O3 has the potential to be used in a number of modern applications, including their applications as supercapacitors, optical coatings, optoelectronic devices, gas sensors, microwave integrated circuits, solar cells, etc. The α-Bi2 O3 phase is the favourite research candidate amongst the different polymorphic forms, due to its high refractive index, good photocatalytic activity and Coatings 2020, 10, 1168; doi:10.3390/coatings10121168 www.mdpi.com/journal/coatings. Coatings 2020, 10, 1168 stability at room temperature, while the α-Bi2 O3 nanostructure is well-known as a visible light active semiconductor. This makes it a very suitable candidate for solid-state white lightening optoelectronics, optical switches, ultra-short pulse generators and nonlinear optical fibre devices [1,5,6,7]. The β-Bi2 O3 on the other hand, has shown tremendous potential in photo-electrochemical and photocatalytic applications [8]
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