This thesis presents results of a study of ZnS:Mn thin film phosphors used in Thin Film ELectroluminescent (TFEL) and Laterally Emitting TFEL (LETFEL) devices, examining techniques for phosphor growth optimisation and post deposition processing in order to strengthen development of novel TFEL devices. To achieve this, thin films of phosphor were deposited using RF magnetron sputtering to investigate the use of co-sputtering in order to optimise dopant concentration. 800 nm films of ZnS:Mn were simultaneously co-sputtered from ZnS and ZnS:Mn (1 wt.%) solid targets. The thin films were deposited at different manganese concentrations by varying the relative RF power applied to each target. The films were deposited directly onto 100 mm diameter (100) n-type silicon substrates, or onto a layer of 300 nm of Y2O3 to fabricate electroluminescent test devices. Luminescence from the phosphor films was characterised via photoluminescent excitation using a 337 nm pulsed N2 laser, with the photoluminescence (PL) optimum obtained at 0.38 ZnS:Mn power ratio. Electroluminescence (EL) from TFEL devices were excited by applying a sinusoidal waveform voltage at a frequency of 1 kHz with maximum luminance obtained at 0.36 ZnS:Mn power ratio.