• Hughes, Mark A.

Abstract

This thesis focuses on two different, but complementary, aspects of the modification ofgallium lanthanum sulphide (GLS) glasses. Firstly the addition of transition metal ionsas dopants is examined and their potential for use as active optical materials is explored.It is also argued that the spectroscopic analysis of transition metal ions is a useful toolfor evaluating the local environment of their host. Secondly femtosecond (fs) lasermodification of GLS is investigated as a method for waveguide formation.Vanadium doped GLS displays three absorption bands at 580, 730 and 1155 nmidentified by photoluminescence excitation measurements. Broad photoluminescence,with a full width half maximum of ~500 nm, is observed peaking at 1500 nm whenexciting at 514, 808 and 1064 nm. The fluorescence lifetime and quantum efficiency at300 K were measured to be 33.4 μs and 4% respectively. Analysis of the emissiondecay, at various vanadium concentrations, indicated a preferentially filled, highefficiency, oxide site that gives rise to characteristic long lifetimes and a low efficiencysulphide site that gives rise to characteristic short lifetimes. X-ray photoelectronspectroscopy measurements indicated the presence of vanadium in a broad range ofoxidation states from V+ to V5+. Tanabe-Sugano analysis indicates that the opticallyactive ion is V2+ in octahedral coordination and the crystal field strength (Dq/B) was1.84. Titanium and nickel doped GLS display a single absorption band at 590 and 690nm, and emission lifetimes of 97 and 70 μs respectively. Bismuth doped GLS displaystwo absorption bands at 665 and 850 nm and lifetime components of 7 and 47 μs. Basedon comparisons to other work the optically active ions are proposed to be Ti3+, Ni+ andBi+, all of these displayed emission peaking at ~900 nm.Through optical characterisation of fs laser written waveguides in GLS, a formationmechanism has been proposed. Tunnelling has been identified as the dominantnonlinear absorption mechanism in the formation of the waveguides. Single modeguidance at 633 nm has been demonstrated. The writing parameters for the minimumpropagation loss of 1.47 dB/cm are 0.36 μJ pulse energy and 50 μm/s scanning speed.The observation of spectral broadening in these waveguides indicates that they mayhave applications for nonlinear optical devices. Fs laser written wave

Topics

• impedance spectroscopy
• photoluminescence
• nickel
• glass
• glass
• strength
• Lanthanum
• titanium
• vanadium
• Bismuth