Investigation of the Structural and Luminescent Properties and the Chromium Ion Valence of Li₂CaGeO₄ Crystals Doped with Cr⁴⁺ Ions

• Main Authors: Dongmei Wang, Xiaowei Zhang, Xinyu Wang, Zhuang Leng, Qianqian Yang, Wen Ji, Hai Lin, Fanming Zeng, Chun Li, Zhongmin Su
• Format: Article
• Language: English
• Published: MDPI AG 2020-11-01
• Series: Crystals
• Subjects: Cr⁴⁺–Li₂CaGeO₄; crystal growth; NIR luminescence property; XPS
• Online Access: https://www.mdpi.com/2073-4352/10/11/1019

Herein<b>, </b>we report on the growth of Cr⁴⁺–Li₂CaGeO₄ crystals by the flux growth method from the flux of LiCl, as well as on the effect of doping Li₂CaGeO₄with Cr⁴⁺ ions on the NIR region spectral properties and crystal structure. The results quantified the occupancy of Cr⁴⁺ in Ge⁴⁺ sites. The emission spectrum presented broad bands in the NIR region, i.e., 1000–1500 nm excited by 980 nm, with maximum peaks at 1200 nm at room temperature caused by the transition of ³T₂→³A₂ in Cr⁴⁺ ions. The lifetime decreased with the Cr⁴⁺ ion doping concentration, specifically from 14.038 to 12.224 ms. The chemical composition and the valence state of chromium in Li₂CaGeO₄ were analyzed using X-ray photoelectron spectroscopy, which showed that the chromium in Li₂CaGeO₄ was tetravalent and no trivalent chromium was found. Therefore, the Cr⁴⁺–Li₂CaGeO₄ crystal has a great potential and future in optical applications.