Coherent and incoherent light generation with rare earth doped crystals

In this thesis fluorides and oxides Pr-doped are characterized as new Solid State sources in the visible range. Since the trivalent Praseodymium ion (Pr) has several transitions in the visible spectral range, it is suitable for both incoherent white light emission and for visible laser emission. Suitable laser diodes based on GaN, emitting in the blue spectral region, have been commercially available since 2003. Compared to the mixing of three colours obtained from three different ions (Er,Tm, Ho usually) the Pr emission efficiency is potentially higher because it is minimized the interaction between energy levels of different ions which can cause quenching of the emission. Moreover the efficiency is not limited by the up-conversion process. Besides, the inorganic bulk fluorides investigated have very low phonon energy (a few hundreds of cm−1 ), and they usually show lower non-radiative decay rates owing to the quenching of radiation. Fluorides are relatively hard, not hygroscopic and not prone to ageing problems therefore they posses a virtually unlimited lifetime and better power scalability than LEDs and OLEDs. This work also investigates other promising rare earth as visible emitters, such as Dysprosium in oxide (YPO4 ) and Europium and Samarium in fluorides (BaY2F8), all this materials has interesting emission in the visible light and could be excited using some inexpensive GaN laser diode, with an emission of ∼ 405 nm. The last part of the thesis regards the coherent light generation in the 1.9 micron regions, that is part of the so called “eye safe” wavelength region. Laser systems that operate in this region offer exceptional advantages for free space applications compared to conventional systems that operate at shorter wavelengths. This gives them a great market potential for the use in LIDAR and gas sensing systems and for direct optical communication applications. The favourable absorption in water makes such lasers also very useful for medical applications.