ORALS

SESSION: AdvancedMaterialsSatPM2-R2	5th Intl. Symp. on New and Advanced Materials and Technologies for Energy, Environment and Sustainable Development
Sat Oct, 26 2019 / Room: Leda (99/Mezz. F)
Session Chairs: Nadezda Stevulova; Liudmila Lisitsyna; Session Monitor: TBA

17:10: [AdvancedMaterialsSatPM212]
Photoluminescence of Phosphors Containing W-O Emission Complexes
Aida Tulegenova¹ ; Liudmila Lisitsyna² ; ¹2Al-Farabi Kazakh National University, Almatу,, Kazakhstan; ²Tomsk State University of Architecrure and Building, Tomsk,, Russian Federation;
Paper Id: 93 [Abstract]

Natural phosphors like MeWO₄, possessing high light emissions at small volumes, are considered to be a promising material for X rays and γ-scintillators. Nanostructured MeWO₄ materials are promising candidates for photoluminescence. During the past decade, unique properties of these materials such as photocatalytic activity, photochromism and electrochromism have attracted the attention of researchers. Photoluminescence in ZnWO₄ crystals, WO₃ crystalline micropowders, as well as in LiF crystals and MgF₂ ceramics doped with tungsten trioxide, was researched at 300 K. Prepared As phosphors were not transparent in the range ≥4 eV (WO₃, ZnWO₄), or they became opaque in this range after doping with tungsten trioxide (LiF crystals, MgF₂ ceramics). Emission was excited by photons with 6>E_ph ≥ 4 eV. The focus of these studies is on the emissions of phosphors with different types of matrices. What they have in common is that the lattices contain W-O polyhedrons. The following was revealed: - Spectral-kinetic characteristics of the phosphors' photoluminescence in the visible range (band at 2.6-2.7 eV) are independent of the width of the band gap (from 13 till 3.8 eV), of the lattice structure of phosphorus matrices and of the method of preparing the materials (grown in air, sintering, laser ablation). - The emission characteristics of phosphors: spectral position of emission band, the value of long-lived time decay, the emission band FWHW and the value of the Stokes shift are similar to those in the WO₃ crystalline micropowder. It looks as if emission centers were created under UV irradiation in specific areas of phosphors with the same properties in all materials under research. - The work deals with a hypothesis according to which the presence of the WO₃ phase in phosphor matrices defines the structure of emission centers (oxygen-depleted polyhedron W⁶⁺nO^2-) and high sensitivity to UV irradiation. The latter is due to the small width of the band gap of the WO₃ lattice (3.8 eV) compared with those in the researched phosphorus matrix lattices. - The emission in the WO₃ material is of a recombination nature. It means that wide-gap dielectric phosphors doped with WO₃ (LiF and MgF₂), free electrons, and holes are created when E_ph<E_g in the matrices. Perhaps, in this case, photocatalytic activity, photochromic, and electrochromic properties are inherent properties of many oxides of transition metals revealed in WO₃-containing materials [1, 2].

References:
[1] J. Grabis, D. Jankovica, M. Kodols, D. Rasmane. Latvian J. Chem., 1/2 (2012) 93-98
[2] G. Huang, Y. Zhu. J. Phys. Chem. C, 111 (2007) 11952-1195