Observation of ESA, ET and thermally enhanced frequency upconversion in Nd3+: LiTeO2glass

Abstract

Infrared to visible upconversion emission bands are observed in Nd 3+ : LiTeO 2 glass at 430, 482, 525, 535, 580, 600, 664 and 766 nm wavelengths due to the 2 P 1/2 4 I 9/2 , 2 P 1/2 4 I 11/2 , 2 P 1/2 4 I 13/2 , 4 G 7/2 4 I 9/2 , 2 P 1/2 4 I 15/2 , 4 G 7/2 4 I 11/2 & 4 G 5/2 + 2 G 7/2 4 I 9/2 , 4 G 7/2 4 I 13/2 and 4 G 7/2 4 I 15/2 transitions, respectively. Mechanisms involved in these upconversion emissions are shown to either involve excited state absorption or energy transfer depending upon the concentration of the rare earth ions. The emission bands at 755 and 968 nm are also observed due to the thermally excited phonon absorption, on excitation with 800 nm wavelength. A 90 fold enhancement in the intensity of anti-Stokes emission at 755 nm is observed in this glass when temperature is raised from 298 to 523 K. Fluorescence intensity ratio (FIR) and sensitivity ( S ) of the two thermally coupled levels viz. 4 F 3/2 and 4 F 5/2 are calculated at different temperatures and results show that these levels could act as temperature sensor in tellurite host. Lifetimes of the excited levels 2 P 1/2 , 4 G 7/2 , 4 F 3/2 , 4 F 5/2 and 4 F 7/2 involved in the emission process are also determined and their temperature dependence is described.