Radiation emitting device

1. A radiation emitting device comprising:

a first electrode, which emits first charge carriers having a first charge during operation;

a first charge carrier transporting layer, which comprises a fluorescent substance and is arranged on the first electrode;

a second charge carrier transporting layer, which contains at least two different phosphorescent substances and is arranged on the first charge carrier transporting layer, the at least two different phosphorescent substances being present as dopants in a charge carrier transportation matrix material; and

a second electrode, which emits second charge carriers having a second charge during operation and is arranged on the second charge carrier transporting layer;

wherein during operation the second charge carrier transporting layer is substantially free of first charge carriers emitted by the first electrode.

2. The radiation emitting device as claimed in claim 1 , wherein the second charge carrier transporting layer is unipolar and can transport only second charge carriers, or blocks first charge carriers.

3. The radiation emitting device as claimed in claim 1 , wherein a unipolar charge carrier transporting layer, which blocks the charge carriers having the first charge or can transport only charge carriers having the second charge, is arranged between the first charge carrier transporting layer and the second charge carrier transporting layer.

4. The radiation emitting device as claimed in claim 1 , wherein the radiation emitting device comprises an organic light emitting diode, and wherein one of the first charge carrier transporting layer, the second charge carrier transporting layer, the phosphorescent substance and the fluorescent substance comprise organic materials.

5. The radiation emitting device as claimed in claim 1 , wherein a recombination of charge carriers having the first charge and charge carriers having the second charge can result in the formation of excitons as excited electronic states, which comprise singlet and triplet excitons.

6. The radiation emitting device as claimed in claim 5 , wherein the excitons formed in the first charge carrier transporting layer comprise triplet excitons, and wherein the phosphorescent substance emits phosphorescent radiation upon excitation by the energy of the triplet excitons formed in the first charge carrier transporting layer.

7. The radiation emitting device as claimed claim 1 , wherein a recombination of charge carriers having the first charge and charge carriers having the second charge takes place only in the first charge carrier transporting layer.

8. The radiation emitting device as claimed in claim 1 , wherein the first electrode is an anode, the first charge carrier transporting layer is a hole transporting and electron transporting layer, the second charge carrier transporting layer is an electron transporting layer, and the second electrode is a cathode.

9. The radiation emitting device as claimed in claim 8 , wherein the second charge carrier transporting layer is a hole blocking, or exclusively electron transporting layer.

10. The radiation emitting device as claimed in claim 1 , wherein the first electrode is a cathode, wherein the first charge carrier transporting layer is a hole transporting and electron transporting layer, wherein the second charge carrier transporting layer is a hole transporting layer, and wherein the second electrode is an anode.

11. The radiation emitting device as claimed in claim 10 , wherein the second charge carrier transporting layer is an electron blocking or exclusively hole transporting layer.

12. The radiation emitting device as claimed in claim 1 , wherein an exciton blocking layer is situated between the second charge carrier transporting layer and the second electrode.

13. The radiation emitting device as claimed in claim 1 , wherein the fluorescent substance comprises an organic material.

14. The radiation emitting device as claimed in claim 1 , wherein the fluorescent substance is present as a dopant in a charge carrier transporting matrix material.

15. The radiation emitting device as claimed in claim 1 , wherein the phosphorescent substance comprises an organic material.

16. The radiation emitting device as claimed in claim 1 , wherein the phosphorescent substances emit with different wavelengths.

17. The radiation emitting device as claimed in claim 16 , wherein the second charge carrier transporting layer has partial regions which each comprise a substance that is phosphorescent at different wavelengths, and the wavelength of the emitted radiation of the phosphorescent substance increases with greater distance from the first charge carrier transporting layer.

18. The radiation emitting device as claimed in claim 1 , wherein HOMO/LUMO levels of the second charge carrier transporting layer are coordinated with the HOMO/LUMO levels of the first charge carrier transporting layer such that no charge carriers having the first charge can pass into the second charge carrier transporting layer.

19. The radiation emitting device as claimed in claim 1 , wherein HOMO/LUMO levels of the second charge carrier transporting layer are coordinated with the HOMO/LUMO levels of the first charge carrier transporting layer such that triplet excitons can pass from the first into the second charge carrier transporting layer.

20. The radiation emitting device as claimed in claim 1 , wherein the thickness of the second charge carrier transporting layer is coordinated with the diffusion length of the triplet excitons, such that the triplet excitons can diffuse through the entire second charge carrier transporting layer.

21. The radiation emitting device as claimed in claim 1 , wherein at least two second charge carrier transporting layers are present and the total thickness of all the second charge carrier transporting layers is less than or equal to the diffusion length of the triplet excitons.

22. The radiation emitting device as claimed in claim 1 , wherein a charge carrier transport path for transporting the first and second charge carriers during operation runs through the device and the charge carrier transport path for the first charge carriers is restricted to that region of the device which is delimited by the first electrode and the first charge carrier transporting layer and the charge carrier transport path of the second charge carriers runs at least through the second charge carrier transporting layer and the first charge carrier transporting layer.

23. A radiation emitting device comprising:

a first electrode which emits first charge carriers having a first charge during operation;

a first charge carrier transporting layer comprising a fluorescent substance and arranged on the first electrode;

at least two second charge carrier transporting layers containing a phosphorescent substance and arranged on the first charge carrier transporting layer; and

a second electrode which emits second charge carriers having a second charge during operation and arranged on the second charge carrier transporting layer;

wherein during operation the second charge carrier transporting layer is substantially free of first charge carriers emitted by the first electrode; and

wherein a total thickness of all the second charge carrier transporting layers is less than or equal to a diffusion length of a triplet exciton.

24. A radiation emitting device comprising:

a first electrode which emits first charge carriers having a first charge during operation;

a first charge carrier transporting layer, which comprises a fluorescent substance and is arranged on the first electrode;

at least two second charge carrier transporting layers, which are arranged on the first charge carrier transporting layer;

wherein each second charge carrier transporting layer comprises a phosphorescent substance which emits at a different wavelength; and

a second electrode which emits second charge carriers having a second charge during operation and is arranged on the second charge carrier transporting layer,

wherein during operation the second charge carrier transporting layer is substantially free of first charge carriers emitted by the first electrode.

25. The radiation emitting device as claimed in claim 24 , wherein the second charge carrier transporting layers are arranged such that the wavelength of the emitted radiation increases with greater distance from the first charge carrier transporting layer.

26. The radiation emitting device as claimed in claim 24 , wherein HOMO/LUMO levels of all the second charge carrier transporting layers are coordinated with one another such that an exciton transfer through all the charge carrier transporting layers can be effected from the first charge carrier transporting layer.