The book focuses on synthesis, characterization and studies on environment stability of thin films of green light emitting small molecules of 8-hydroxyquinoline metal complex (Alq3, Inq3 and Znq2) deposited at different deposition conditions using thermal evaporation. The characterization tools like UV-Vis,IR, photoluminescence, spectroscopic ellipsometry, atomic force microscopy (AFM) and lifetime measurements are used. Degradation studies are presented on these films. Effect of air, moisture, exposure to white light on these films is shown. The change in photoluminescence properties, morphology and possibilities of formation of new phase is also predicted. To see the influence of deposition conditions on the nucleation and growth of thin films which affect the film microstructure and hence the physical and device properties,the influence of deposition rate and substrate temperature on environmental stability is shown.The tendency of blue shift in PL peak position of organic films is exploited by converting green light emitting Znq2 film to blue.