Random Lasers (RLs) are realized in disordered media with gain; the feedback for stimulated emission of light is given by the scattering and no external cavity is needed. The cavity is given by multiple scattering. Therefore, when light rays penetrate these materials they interfere with each other because of scattering and, by different material-dependent mechanisms, they establish standing modes.
In a RL the multiple scattering process defines optical modes with a certain central frequency and bandwidth, lifetime and a rich spatial profile. Recently promising methods for the fabrication of planar lasers are referred to RLs and are based on active molecular layers in which defects, aggregates or external beads behave as scattering centers. To build a RL it is important to create strong enough scattering for the material to become optically thick. However, due to the intrinsically randomness of the scattering centers, conventional methods for the fabrication of RLs do not allow for a careful control of the device geometrical parameters, and in turn of the lasing properties. We describe the use of semiconductor organic materials for RL devices in term of physical-chemical properties, characteristics and advantages. Non-conventional self-organization and lithographic processes have been used for the realization of nanoscale organic random lasers. For the first time, the glassy nature of RL spectral intensity fluctuations was experimentally demonstrated in a solid disordered system.