Emisión láser en películas delgadas

Abstract

In this work we make an approach to some spectroscopy related concepts such as luminescence, emission spectra, the characteristics of absorption and emission, laser and amplified spontaneous emission. We address specifically the concept of fluorescence as it is the phenomenon in which the current line of investigation of this work is based, starting by giving a theoretical background in some basic aspects and then proceeding to a more detailed study of our state-of-the-art samples, commenting the importance of each one of the samples separately and focusing in the optical properties that make them some of the most important components in the field. These samples are thin film composites with different active layers including the organic polymer poly[2-methoxy-5-(2’- ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV), the organic semiconductor 5,6,11,12- Tetraphenyltetracene (rubrene) and organometallic T iO2 perovskites. These material have an extensive literature being one of the most popular topics due to their high charge carrier mobility, astounding growth rates of their efficiencies, advantageous costs of production, among other issues. We set the main objectives: the optical the characterization of the different materials, and the analysis of various types of setups to try to obtain different types of emission like laser, or amplified spontaneous emission. We show the specifications of the samples of rubrene, perovskites and MEH-PPV; to cover the characteristics of the thin film composites. Then we briefly talk about the devices used for the optical characterization, mentioning some of their specifications and proceed to show the set ups that we utilized for the absorption, emission, lifetimes, etc. A theoretical background is given for a better comprehension of the results derived from the optical characterization. The experimental results are displayed and discussed separately for each one of the materials. We study thoroughly the processes that take place, highlighting the particular peculiarities of each sample. For the rubrene samples the absorption spectrum was analyzed for different samples and their lifetimes were studied according to the diagram levels of the rubrene. No ASE emission was observed. For the perovskite based samples we study the lifetime of compact and porous perovskites, giving also an analysis of their emission spectra. For the MEH-PPV we start with the absorption and emission spectra of different composites, no laser phenomenon was observed for the samples but narrow emission peaks were observed, showing variable wavelength according to the angle of detection; as well as ASE, whose threshold power was studied for the different composites. All the results were compared with those that can be found in the literature and delve into the possible causes for ones that do not adjust to what we expect. Finally we sum up the measurements we made and present the conclusions we reached in this project.