Crystalline-structure-dependent green and red upconversion emissions of Er 3+–Yb 3+–Li + codoped TiO 2

• Published in: Optics communications Vol. 284; no. 13; pp. 3311 - 3314
• Main Authors: Cao, B.S., He, Y.Y., Feng, Z.Q., Song, M., Dong, B.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 2011
• Subjects: Crystal structure; Luminescence; Optical materials; Sol–gel growth; Sol–gel growth; Luminescence; Optical materials; Crystal structure
• ISSN: 0030-4018; 1873-0310
• DOI: 10.1016/j.optcom.2011.03.005

Crystalline structures and infrared-to-visible upconversion luminescence spectra have been investigated in 1 mol% Er 3+, 10 mol% Yb 3+ and 0–20 mol% Li + codoped TiO 2 [1Er10Yb(0–20)Li:TiO 2] nanocrystals. The crystalline structures of 1Er10Yb(0–20)Li:TiO 2 were divided into three parts by the addition of Yb 3+ and Li +. Both green and red upconversion emissions were observed from the 2H 11/2/ 4S 3/2 → 4I 15/2 and 4F 9/2 → 4I 15/2 transitions of Er 3+ in Er 3+–Yb 3+–Li + codoped TiO 2, respectively. The green and red upconversion emissions of 1Er:TiO 2 were enhanced significantly by Yb 3+ and Li + codoping, in which the intensities of green and red emissions and the intensity ratio of green to red emissions ( I green / I red ) were highly dependent on the crystalline structures. The significant enhanced upconversion emissions resulted from the energy migration between Er 3+ and Yb 3+ as well as the distortion of crystal field symmetry of Er 3+ caused by the dissolving of Li + at lower Li + codoping concentration and the phase transformation at higher Li + concentration. It is concluded that codoping with ions of smaller ionic radius like Li + can efficiently improve the upconversion emissions of Er 3+ or other rare-earth ions doped luminsecence materials. ► Crystalline structures of Er:TiO2 are divided into three parts by Yb and Li codoping. ► Green and red UC emissions are strongly dependent on the crystalline structures. ► Change of Er symmetry and phase structure by Li codoping enhanced UC emissions.