Observation of ESA, ET and thermally enhanced frequency upconversion in Nd³⁺: LiTeO₂ glass

Laser and Spectroscopy Laboratory, Department of Physics, Banaras Hindu University, Varanasi – 221005, India

Corresponding author: sbrai49@yahoo.co.in

Received: 28 July 2007
Accepted: 19 November 2007
Published online: 6 February 2008

Abstract

Infrared to visible upconversion emission bands are observed in Nd³⁺: LiTeO₂ glass at 430, 482, 525, 535, 580, 600, 664 and 766 nm wavelengths due to the ²P_1/2   ⁴I_9/2, ²P_1/2   ⁴I_11/2, ²P_1/2   ⁴I_13/2, ⁴G_7/2   ⁴I_9/2, ²P_1/2   ⁴I_15/2, ⁴G_7/2   ⁴I_11/2 & ⁴G_5/2+²G_7/2   ⁴I_9/2, ⁴G_7/2   ⁴I_13/2 and ⁴G_7/2   ⁴I_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. ⁴F_3/2 and ⁴F_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 ²P_1/2, ⁴G_7/2, ⁴F_3/2, ⁴F_5/2 and ⁴F_7/2 involved in the emission process are also determined and their temperature dependence is described.