Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Patent
1996-08-15
1998-06-16
Patel, Ashok
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
313502, 313506, 428917, 428690, B32B 3300, C09K 1170, H01J 6144
Patent
active
057676224
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an electroluminescent system having a substance which is light-emitting when an electric voltage is applied.
2. Description of the Related Art
Electroluminescent systems are known. In these, either inorganic or organic substances are used which can be excited by means of an electrical voltage to send out light beams. As inorganic substances, for example, monocrystalline III-V or II-IV semiconductors and powdered ZnS compounds are used which may be doped differently. The drawback in these electroluminescent, inorganic systems is that high alternating voltages must be available as operating voltage. If these electroluminescent, inorganic systems are intended to be used, for example, in motor vehicles for the lighting of display instruments, the battery charge which is present in the motor vehicle as direct voltage must be converted accordingly. On the one hand, this voltage conversion is very complex and, because of the operation at high alternating voltages, it also requires an additional electromagnetic compatibility protection for further electronic systems of the motor vehicle.
Furthermore it is known to use electroluminescent, organic substances, for example, polymers, dyes, polymers doped with molecules and polymer blends. Here, it is a drawback, however, that the organic substances have an insufficient long-time stability, particularly a thermal and/or chemical stability. This means that the use of electroluminescent systems with organic substances is not possible in practical applications, for example, for the lighting of display instruments in motor vehicles.
SUMMARY OF THE INVENTION
In contrast, the electroluminescent system having a substance which is light-emitting when an electric voltage is applied, characterized in that the light-emitting substance (12) is formed by inorganic particles (22) which are connected with one another via organic spacers (26), offers an advantage that an electroluminescent system, which can be produced in a cost-advantageous manner and which is versatile in its applications, can be accomplished in a simple manner. Since the light-emitting substance is formed by inorganic particles, which are connected with one another via organic spacers, it is possible in an advantageous manner to obtain a light-emitting substance wherein the desired electrical, electronic, chemical, and mechanical properties can be achieved in a purposeful way. By means of the inorganic particles, which are connected with one another via the organic spacers, a binary system is created wherein the inorganic particles take over the electron conductivity of the light-emitting substance, while the organic spacers take over the mechanical stabilization of the light-emitting substance and the generation of the light radiation. Therewith, the properties of the inorganic particles are ideally combined with those of the organic spacers so that, by way of optimizing the inorganic particles as well as the organic spacers to fit their specific application, light-emitting substances can be accomplished that have a high thermal and/or chemical stability and that are provided with high quantum efficiency during electroluminescence. By means of a targeted installation of functional groups in the organic spacers it is possible to purposefully influence the probability for a radiant recombination of electrons and holes so that a high luminous efficiency can be accomplished with the light-emitting substance according to the invention.
An advantageous embodiment of the invention provides that the organic spacers are formed by an organic, e.g., sphere preferably an organic ligand, e.g., sphere. The organic ligand envelope determines the positioning of the inorganic particles within the light-emitting substance because the ligand envelopes enter into a chemical combination with one another which determines the mechanical stability of the substance and thus the position of the inorganic particles. By selecting a thickness for the ligand env
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Colvin et al; Light emitting diodes made from cadmium selenide nanocrystalsand a semiconducting polymer, Aug. 1994.
Fenske Dieter
Hueppauff Martin
Schmid Guenter
Patel Ashok
Robert & Bosch GmbH
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