This lab specializes in optical spectroscopy and microscopy, in particular spectroscopy at low temperatures with high spectral and also temporal resolution (picoseconds). Some of the techniques employed are, for example, pump-probe spectroscopy in the nanosecond to millisecond time range, spectral hole burning (SHB), time-correlated single photon counting (TCPS), Raman spectroscopy, confocal optical microscopy, and near field optical microscopy. Another focus of our work is phase-sensitive ultrasonic probing of the mechanical properties of nanometric objects, including organic and inorganic thin films, in the MHz to GHz frequency range. The complete photophysic characterization of conjugated materials (organic, inorganic and also biologic materials) and optoelectronic devices can be accomplished in this lab equipped with spectroscopic techniques that cover the entire spectrum, from UV to mid-infrared are available: transmission and reflection spectroscopies, fluorescence and phosphorescence spectroscopies with a resolution between 2 ps and milliseconds, photoinduced absorption spectroscopy time resolved in a regime ranging from 30 fs to milliseconds, electroabsorption spectroscopy, a femtosecond laser equipment, and other electromodulación techniques. Equipment is optimized to detect signals at low optical intensity, as in photovoltaic devices (due to low solar radiation) and molecular electronics (due to low number of molecules). Measurements are made in environmentally controlled or high vacuu, at room temperature or down to 1.5 ºK. The samples studied are samples in solution, in films of varying thickness and optoelectronic devices, being in the latter case possible to test the optical properties during operation. This lab includes the following Advanced Characterization Services: - Steady State Electroabsorption spectroscopy. This technique is a useful tool to characterize anionic and cationic features in organic semiconductors. In addition it is a very helpful technique for understanding degradation mechanisms in organic light emitting diodes. Field induced electroabsorption studies allow to elucidate the built-in field across the device active area which is intrinsically related to the work-function difference between cathode and anode. Formation of oxide at the electrodes or chemical impurities at the organic-inorganic interface can therefore be revealed by the associated change in built-in field. - Photoconductivity measurements. Characterization of the spectral response of photodetectors and solar cells is another activity that can be provided by our laboratory. We can also provide a range of different services such as measuring the monochromatic spectral response, determination of the external quantum efficiency and current-voltage characteristics. - Transient absorption measurements. We can monitor dynamics of long-lived excited states such as unrelaxed polarons or triplet states. The temporal window detection of this experiment expands from 1 ns to 100 ms. These type of studies are for instance relevant for characterization of photosensitizers in photodynamic therapy, studies of light harvesting biological complexes and characterization of charged states in organic disordered systems. - Pump-probe spectroscopy. The early dynamics (30 fs – 1ns) of excited states in semiconductors can be probe with this technique. The nature of these states as well as their main decay mechanisms are unravelled by probing across the visible and near infrared. Upon exciting at high fluences it is possible to reveal the presence of annihilation processes which are intrinsically related to the exciton mobility. In molecular materials charged excitations (polarons) can be spectrally distinguish from Frenkel excitons. Monitoring polaron absorption provides information on polaron mobility and recombination processes, of crucial importance for optoelectronic devices
