![]() ![]() Since they are shielded by outer 5s 2 and 5p 6 orbitals, electrons from 4f orbitals do not participate in bonding and are only slightly affected by the surroundings of the ions. With the absence of 57La and 71Lu, RE atoms, all have incompletely filled 4f orbitals that are positioned in the inner shell of xenon electron configuration, which are responsible for their emission properties. However, they are costly but highly efficient for many technological applications, mainly in lighting and display devices. Even though the group is regarded as rare earth elements, they are not particularly rare. Because of many similarities, such as ionic +3 charges and similar ionic radius, 39Y that also belongs to the III transition group and is positioned just above 57La is also often considered as a part of the RE group. Rare earth (RE) elements are sixth period elements in the periodic table, from 57La to 71Lu. A better understanding on these topics may progress the desired design of this kind of material towards specific applications. It is of great importance to summarize publications on rare earth‐doped anatase TiO2 nanoparticles to find correct TiO2-RE combination to sensitize trivalent rare earths luminescence, as well as to predict or tune structural and morphological properties. Visible (VIS) and ultraviolet (UV) luminescence of several RE3+ ions can be obtained when incorporated into anatase TiO2, also affecting microstructural characteristics of TiO2. It is a challenge to optimize the synthesis procedure to incorporate rare earth RE3+ ions into the TiO2 structure due to large mismatch in ionic radii between the Ti4+ and RE3+ and because of the charge imbalance. Also, by doping TiO2 with optically active ions, visible light via up‐ or downconversion luminescence can be produced. Doping of TiO2 with various ions can increase the photocatalytic activity by enhancing light absorption in visible region and can alter structure, surface area and morphology. Because of the high photocatalytic activity, anatase is a preferred TiO2 form in many applications such as for air and water splitting and purification. The FESEM study indicated that the surfaces of the particles are highly roughened on milling and particles are agglomerated.Titanium dioxide is a wide band‐gap semiconductor of high chemical stability, nontoxicity and large refractive index. The PL study showed the lowering of emission peaks in the milled powder, which is primarily due to the presence of defects. The variation in the band gap is attributed to the combined effect of particle size and phase content of the powder. UV-visible absorption spectra showed that the band gap energy of the milled powder varies between 3.1 to 3.37 eV for direct transition. A phase diagram of the different phases of TiO2 under different milling time has been obtained. The volume fraction of srilankite first increased and then decreased with increase of milling time. Milling was found to reduce the volume fraction of the anatase and increase that of the rutile with increasing milling time. XRD showed transformation from anatase to srilankite (an intermediate high-pressure form of TiO2) and then to rutile with increasing milling time to 10 hrs. Evolution of the structure and microstructure of the powder with milling time was studied by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Photoluminescence (PL) and UV-Visible spectroscopy. A series of TiO2 powder in anatase form was ball milled at a speed of 300 rpm at room temperature and ambient pressure with ball-to-powder weight ratio 10:1 for different milling time. ![]()
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