Optical spectroscopy of rare earth ions in glasses

Abstract

The relationships between host glass composition and optical properties of rare earth ions were studied by means of absorption and emission spectroscopy. Eu³⁺ and Tb³⁺ were found to be appropriate indicator ions for determining the properties of the local environment around rare earth ions. Er³⁺ and Nd³⁺ ions are widely used in lasers and amplifiers. The knowledge of the compositional influence on the spectroscopic parameters of rare earth ions enabled the modeling of the emission properties of important Er³⁺ and Nd³⁺ transitions in order to figure out the Optimum host glasses. Fluoride phosphate and phosphate glasses are attractive candidates for lasers and amplifiers. In these glasses, the degree of covalency between the rare earth ions and surrounding ligands mainly affects the spectroscopic parameters of rare earth ions such as Judd-Ofelt parameters and electron-phonon coupling strength. The increase of the electron-phonon coupling strength with the phosphate content is responsible for the decrease of the Er³⁺ emission intensity at 540 nm. Otherwise, it increases the Er³⁺ emission intensity at 1.5 µm in the fluoride phosphate glasses. The lower microparameters of Nd³⁺ cross relaxation in phosphate glasses cause the higher lifetimes of the Nd³⁺ ⁴F₃/₂ laser State at higher Nd³⁺ concentrations with respect to fluoride phosphate glasses. The energy transfer to OH groups in phosphate glasses decreases the hfetime and emission intensity of the laser State of both Er³⁺ and Nd³⁺ ions.