Laser diodes organic lasers

Sakai K, Tsuzuki T, Itoh Y et al (2005) Using proton-transfer laser dyes for organic laser diodes. Appl Phys Lett 86 081103... 

GaN as a semi-conducting material for electronics is about to be launched on the market, especially for the use in blue- and UV-emitting LEDs and laser diodes [2]. The material is deposited on crystalline substrates like sapphire using thin-film epitactical techniques. Often, metal-organic chemical vapor deposition (MOCVD) is used. The necessity for such technologies limits the production rate and pushes up costs. 

P. A. Johnson, T. E. Barba , B. W. Smith, and J. D. Winefordner, Ultralow detection limits for an organic dye determined by fluorescence spectroscopy with laser diode excitation, Anal. Chem. 61, 861-863 (1989). 

The use of conjugated light emitting polymers in the construction and commercialisation of organic LEDs is described in the section 3.8.6 on electroluminescence phenomena of Chapter 3. The rapid expansion of the development work on LEDs has inevitably led to the examination of luminescent conjugated polymers as materials for constructing laser diodes. 

From the first synthesis of rare-earth /9-diketonates in 1897 by Urbain until now, hundreds of different complexes formed by reaction between Lnni ions and /3-diketone derivatives have been described in the literature. Interest for this type of complexes comes from then-potential application in numerous and diverse domains. These complexes can be used for example as extractants in solvent-solvent extraction processes or as active compounds for the development of chelate lasers or liquid lasers. But they can also find applications in NMR as shift reagents or as electroluminescent materials in organic light-emitting diodes (OLEDs) (Binnemans, 2005b). 

Crystalline silicon is the most widely used semiconductor material today, with a maiket share of above 90%. Because of its indirect electronic band structure, however, the material is not able to emit light effectively and therefore carmot be used for key applications like light-emitting diodes or lasers. Selected one- or two-dimensional silicon compounds like linear or branched polysilylenes [1] or layered structures like siloxene [2], however, possess a direct band gap and therefore exhibit intense visible photoluminescence. Siloxene, a solid-state polymer with a sheet-like layered structure and an empirical formula Si H (OH) , in particular, is considered as an alternative material for Si-based liuninescent devices. Detailed studies of stmctural and photophysical properties of the material, however, are strraigly impeded by its insolubility in organic solvents. 

The last example of this section deals with the optical function of hole-transport layers. In OLEDs some light is waveguided in the combined anode/organic layers due to total internal reflection [44], By increasing the thickness of the hole conductor the emitter can be optically decoupled from the contact. In a series of devices with increasing thickness of the hole conductor, deposited subsequently from solution, it was shown that a HTL thickness larger than 300 nm was necessary to accomplish this. As a very sensitive measure the threshold of amplified spontaneous emission (ASE) was used (Fig. 9.18, [45]). This is an important result with respect to a potential electrically driven organic laser diode. 

There are several prerequisites for the realization of an electrically driven organic laser diode. Aside from a low-threshold active organic material a suitable resonator structure incorporating electrical contacts has to be found. 

The challenge on the way to the electrically driven organic laser diode is therefore to find a laser material with a low-threshold and a quantum efficiency that is relatively independent of current density and electric field [14]. 

---