Synthesis and study of spectroscopic properties of CdF2 crystals codoped with luminescent rare earth ions (Ho3+/Yb3+)

In this paper, we report the optical analysis of Ho3+ ions doped CdF2 single crystals. The pulled crystals were prepared by use of the Bridgman technique from a vacuum furnace in fluoride atmosphere after purification of the starting materials. Absorption, excitation, emission and fluorescence decay spectra were recorded at room temperature. The Judd-Ofelt (JO) analysis was applied to obtain the three phenomenological intensity parameters (Omega(t), t = 2, 4, 6) and the transition strengths. The JO intensity parameters Omega(2),Omega(4) and Omega(6) for 4f-4f transitions of Ho3+ ions were computed from the optical absorption spectra using UV, visible and near infrared transitions. These parameters were then used to calculate the radiative transition probabilities (A(JJ')), branching ratios (beta(JJ')) and radiative lifetimes (tau(rad)) of the main laser emitting levels of Ho3+ ions. The obtained spectroscopic properties are compared to those of Ho3+ transitions in other fluoride and oxide hosts. The excitation spectrum in the UV-Visible spectral range is very close to the absorption spectrum indicating that all observed absorption levels can excite the holmium green emission corresponding to (5)F4(S-5(2))-> I-5(8) transition. The emission spectrum is mainly dominated by the green emission alongside the blue and red emissions. For the main transitions, there is a good agreement between the emission spectrum and the spontaneous emission probabilities given by the JO analysis. Using the Fuchtbauer-Ladenburg method, the emission cross-section of the three main visible emission were determined in addition to other important laser parameters such radiative quantum efficiency and optical gain. We discuss the mechanisms of energy transfer in a forthcoming publication. (C) 2014 Elsevier B.V. All rights reserved.