Luminescence electroluminescent materials

A.H. Kitai, editor, Solid State Luminescence Theory, materials and devices. Chapman and Hall, London, 1993. A multi-authored book on many topics in the field of luminescence and luminescent materials. Many topics are discussed the stress on electroluminescence is strong. 

A new class of silicon-containing copolymers was synthesized by the Heck reaction of distyrylsilane monomers with thiophene and thieno[3,2-fe]thiophene derivatives, their luminescence properties were studied, and these polymers were demonstrated to be promising electroluminescent materials (2001SM1743, 2002MI5). 

Certainly one of the most interesting applications lies in the control of architecture (control of hole and electron injecting and active layers) in very thin electroluminescent devices. The existence of a precursor polyelectrolyte Pre-PPV (39,90,91) of the electroluminescent material poly(p-phenylene-vinylene) (PPV) (92) makes it possible to fabricate polyion multilayer film architectures, in which the Pre-PPV can subsequently be converted to PPV by thermal annealing (19,34-38,87,88,93). The first electroluminescent devices have been prepared and it was found that devices as thin as 13 nm emit light (88). Tum-on voltages of less than 2 V are required to generate light (35) and even an influence of the film architecture on the luminescent properties has been observed (88). However, the structural details of these films are presently not understood and it is not clear how device properties are influenced by film composition and architecture. We have recently shown that the thermal conversion of Pre-PPV to PPV can be carried out with preservation of a layered structure. These results were obtained by neutron reflectometry on... 

V and 1 GHz, respectively. A ne v nonconjugated polymer electroluminescent material, including stilbene derivatives, vas patented [19]. The preparation process for this electroluminescent material involved monomer synthesis and polymer synthesis. The author suggested that this electroluminescent material can be used in electroluminescent devices, luminescent devices, and so on. 

Electroluminescent diodes are not the only way of practical appUcadon of luminescence. Luminescence of materials subjected to action of various types of electromagnetic radiation is used for its detection, for road signs visible at dusk and at night, and many other applications. 

S. S. Chadha. 1993. Powder electroluminescence. In Solid State Luminescence Theory, Materials and Devices, ed. A. H. Kitai. New York Chapman Hall. 

Lanthanide p-diketonates are amongst the best smdied rare-earth luminescent complexes [58]. They are brightly luminescent and volatile so that incorporation into various electroluminescent materials is simple. Moreover their photophysical properties are easily tuned by a judicious choice of ancillary ligands. Indeed, conventional synthesis usually yields bis(hydrated) lanthanide tris(P-diketonates), but the two solvent molecules can be substituted by either a fourth diketonate anion or a donor ligand with adequate functionalisation as to provide convenient light harvesting and subsequent energy transfer onto the metal ion. It is noteworthy that not only visible but also near-infrared luminescence [59,60] is efficiently sensitised in lanthanide p-diketonates. In the case of Eu , some ternary complexes have quantum yields up to 85% [8] and the main asset of their luminescent properties is an emission essentially concentrated in the hypersensitive Dq transition... 

In electroluminescence devices (LEDs) ionized traps form space charges, which govern the charge carrier injection from metal electrodes into the active material [21]. The same states that trap charge carriers may also act as a recombination center for the non-radiative decay of excitons. Therefore, the luminescence efficiency as well as charge earner transport in LEDs are influenced by traps. Both factors determine the quantum efficiency of LEDs. 

Polarized luminescence from oriented molecular materials 1999 Ladder-type materials 1999 Electroluminescence in organics... 

Spiro-FPAl/TPBI/Bphen Cs/Al. A very low operating voltage of 3.4 V at luminance of 1000 cd/m2 was obtained, which is the lowest value reported for either small-molecule or polymer blue electroluminescent devices. Pure blue color with CIE coordinates (0.14, 0.14) have been measured with very high current (4.5 cd/A) and quantum efficiencies (3.0% at 100 cd/m2 at 3.15 V) [245]. In another paper, Spiro-FPA2 (126) was used as a host material with an OLED device structure of ITO/CuPc/NPD/spiro-FPA2 l%TBP/Alq3/LiF that produces a high luminescent efficiency of 4.9 cd/A [246]. 

Blue luminescent materials for organic electroluminescent devices White light-emitting organic electroluminescent devices Blue organic electroluminescent devices... 

The second claim by lida et al. (2007) refers to a composite of an organic electroluminescence device comprising a luminescent material and triarylamine cation-radicals that open a possibility to use a lowered working voltage and to enhance the device durability. Scheme 8.7 represents one of the examples from this patent. 

Poly( -phenylene vinylene) (PPV) was the first reported (1990) polymer to exhibit electroluminescence. PPV is employed as a semiconductor layer. As noted earlier, the layer was sandwiched between a hole-injecting electrode and electron-injecting metal on the other. PPV has an energy gap of about 2.5 eV and thus produces a yellow-green luminescence. Today, other materials are available, which give a variety of colors. 

The use of luminescent materials, the subject of Chapter 3, which was at one time confined largely to the production of fluorescent lamps and cathode ray tubes has spread further into everyday life. It is a common sight to see phosphorescent safety signage in low-light environments, to wear fluorescent garments, to look at electroluminescent displays and to use light emitting diodes in trafhc control and vehicle... 

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. 

Semiconductor band-gap luminescence results from excited electrons recombining with electron vacancies, holes, across the band gap of the semiconductor material. Electrons can be excited across the band gap of a semiconductor by absorption of light, as in photoluminescence (PL), or injected by electrical bias, as in electroluminescence (EL). Both types of luminescence have been used in chemical sensing applications [1,3]. 

---