Up-conversion processes in Nd3+-doped chloro-sulfide glasses

Up-conversion processes of Nd3+ ions are studied in low phonon energy halogeno-sulfide glasses based on GeS2,Ga2S3 and CsCl. Samples are prepared in sealed silica ampoules heated at 925°C in a tubular rocking furnace. Up-conversion spectra are recorded at room temperature and liquid-nitrogen temperature, with continuous excitation from a Ti-sapphire ring laser. The addition of CsCl to the GeS2–Ga2S3 sulfide glass results in a shift of the bandgap towards shorter wavelengths. Thus, emission from larger energy states of Nd3+ can be observed in CsCl containing glasses. Blue emission from the 2P1/2 state and green, yellow and red emissions from 4G7/2 are observed with excitation at 818 nm, within the 4F5/2 state. A 2-photon mechanism with pump excited state absorption (ESA) is responsible for this up-conversion process. Excitation at 888 nm into 4F3/2 results in the green, yellow and red emissions only. In that case, two mechanisms are proposed: energy-transfer up-conversion (ETU) and signal ESA.