The Study Of MIR Luminescence Properties Of Dy³⁺-doped Ge-Ga-S-CsI Chalcohalide Glasses

Chalcogenide glass is one kind of excellent infrared optical materials, with low phonon energy, high transmittance from visible to far-infrared spectra. It also possesses higher second- and third- order optical nonlinearities comparing to oxide glass. Halides doped chalcogenide glass system can widen optical transmittance range, improve rare-earth solubility and reduce the energy gap. In this paper, our studies mainly focus on the optical properties and energy transfer mechanisms of Dy3+ doped in Ge-Ga-S-CsI system.Absorption cross-section of the 6H11/2 and 6H13/2 levels and emission cross-sections of the 2.7 and 4.2μm fluorescences in Dy3+-doped Ge-Ga-S glasses increased with decreasing sulfur concentration. Measured lifetimes of the two energy levels also increased at the same time due to the reduced non-radiative relaxation rates. The non-radiative relaxations quenching the lifetimes of 6H13/2 and 6H11/2 manifolds are cooperative upconversion processes of the following types, i.e., 6H13/2,6H13/2→6H15/2, [6F11/2, 6H9/2] and 6H11/2, 6H13/2→6F9/2-6H7/2, 6H15/2. The existence of these types of energy transfers was confmned by the analysis using the rate equations. Rate of these cooperative upconversions was small for 60GeS₂-30Ga₂S₃-10CsI (c) with less content of sulfur.Effects of CsI addition to Ge-Ga-S glass on the MPR as well as emission characteristics of Dy3+ were also investigated. The oscillator strengths of the excited manifolds in Dy3+-doped Ge-Ga-S-CsI glass were smaller than those for Ge-Ga-S glass. It is from the weaker perturbation of rare-earth by more ionic nature of bonds between cations and I- than sulfur. Addition of CsI resulted in the reduction of the MPR rate as well as the enhancement in quantum efficiencies of the mid-infrared fluorescence. CsI's addition to Ge-Ga-S glass did not change the phonon energy participating in the MPR processes which is 375cm-1 by asymmetrical stretching vibration of [GeS₄] tetrahedra. However, the addition of CsI caused the broadening of the excited manifolds and consequently, it diminishes the population of the lowest Stark component of the excited manifold with increasing temperature. Therefore, the MPR rates for CsI-containing glasses increased more slowly than that for Ge-Ga-S glass with temperature. Furthermore, electron-phonon coupling strength was reduced in Ge-Ga-S-CsI glass and consequently decreased the MPR rates. Besides, adding CsI into chalcogenide glass system can improve rare-earth solubility as well as glass forming ability.