Effects of Cr3+ addition on the structure and optical properties of α-Zn2SiO4 synthesized by sol-gel method. Issue 1 (January 2018)

• Record Type: Journal Article
• Authors: Babu, B. Chandra; Wang, Gui-Gen; Yan, Bo; Yang, Qi; Baker, Andrew P.
• Is Part Of: Ceramics international. Volume 44:Issue 1(2018)
• Page Start: 938
• Page End: 946
• Publication Date: 2018-01
• Subjects: Structure -- Zn2SiO4 -- Coordination -- XRD -- XPS -- Raman and photoluminescence; Ceramics -- Periodicals; Céramique industrielle -- Périodiques; Ceramics; Periodicals; Electronic journals; 666
• DOI: 10.1016/j.ceramint.2017.10.026
• Languages: English
• ISSNs: 0272-8842

Abstract

Abstract: The α-Zn2 SiO4 (willemite) structure is known as an extremely versatile host matrix for phosphors. Here we show that Cr 3+ has very low solubility in α-Zn2 SiO4 ， and powder x-ray diffraction confirms that ZnCr2 O4 spinel is segregated even at 0.05 mol% Cr addition， while Raman spectroscopy shows that a silicate phase is segregated at the same 0.05 mol% Cr addition and these results confirm that both Zn 2+ and Si 4+ vacancies occur with the addition of Cr 3+ to α-Zn2 SiO4 and charge neutrality requires that two Cr 3+ ions are needed for each Zn 2+ and Si 4+ vacancy. The small addition of Cr 3+ to α-Zn2 SiO4 results in a small lattice expansion and because the Cr–O and Zn–O bond lengths are similar, and the Si–O bond length is shorter, it is expected that the Cr 3+ ion is closer to the Si 4+ vacancies resulting in a lattice expansion. This is supported by X-ray photoelectron spectrometry which shows that the binding energy of Si 2p, and especially O 1s, are more affected by Cr 3+ addition than Zn 2p binding energy. The UV–vis absorption spectrum for α-Zn2 SiO4 :Cr 3+ confirms that the Cr 3+ d 3 ion is in its preferred octahedral coordination but the photoluminescence (PL) measurements show emission in the yellow red region (CIE coordinates x = 0.52 and y = 0.45), rather than red, suggesting that the octahedral coordination for Cr 3+ is distorted. The results confirm that the Cr 3+ is not sited in either of the non-equivalent tetrahedral sites for Zn 2+ in α-Zn2 SiO4, as is typically reported for the other cations added to the host lattice.