Electroluminescent device

1. An electroluminescent device, comprising:

first and second electrodes that are at least partially transparent in a spectral domain;

an electroluminescent layer that lies between the first and second electrodes and that is suitable for emitting electromagnetic radiation in the spectral domain, the electromagnetic radiation being circularly polarized in a first polarization direction;

a structured substrate, the first electrode lying between the structured substrate and the electroluminescent layer, the structured substrate comprising:

features that are reflective in the spectral domain, and that possess a hollow geometric shape configured so that electromagnetic radiation that passes through the first electrode is reflected from the reflective features while preserving the first polarization direction,

a filler material that is transparent in the spectral domain and that is arranged to fill the reflective features so that the structured substrate has a planar surface.

2. The device according to claim 1 , wherein the hollow geometric shape of the reflective features is configured so that electromagnetic radiation that passes through the first electrode is reflected from the reflective features N times, N being a non-zero even integer number.

3. The device according to claim 1 , wherein the reflective features have at least one V-shaped profile.

4. The device according to claim 1 , wherein the reflective features comprise inclined flanks that make an angle comprised between 30° and 60° with respect to the normal to the planar surface of the structured substrate.

5. The device according to claim 1 , wherein the reflective features are of concave shape, and the structured substrate comprises a matrix array of microlenses forming the filler material.

6. The device according to claim 1 , wherein the reflective features are periodically distributed in a direction perpendicular to the normal to the planar surface of the structured substrate.

7. The device according to claim 6 , wherein the electromagnetic radiation possesses a dominant wavelength, denoted λ, and the reflective features have a spatial period longer than 5λ, and preferably longer than 10λ.

8. The device according to claim 1 , wherein the electromagnetic radiation possesses a dominant wavelength, denoted λ, and the reflective features have a depth larger than 5λ.

9. The device according to claim 8 , wherein the depth, denoted H, and the spatial period, denoted P, respect H=P/2.

10. The device according to claim 1 , wherein the reflective features are made of a metal chosen from Ag and Al.

11. The device according to claim 1 , wherein the electroluminescent layer is made of a chiral organic material.

12. The device according to claim 1 , wherein the first and second electrodes are made of a transparent conductive oxide.

13. The device according to claim 1 , wherein the spectral domain is chosen from:

the visible domain with wavelengths comprised between 400 nm and 780 nm,

the UV-A domain with wavelengths comprised between 315 nm and 400 nm,

the near-infrared domain with wavelengths comprised between 780 nm and 3 μm.

14. The device according to claim 1 , wherein the reflective features comprise inclined flanks that make an angle comprised between 40° and 50° with respect to the normal to the planar surface of the structured substrate.

15. The device according to claim 1 , wherein the electromagnetic radiation possesses a dominant wavelength, denoted λ, and the reflective features have a depth larger than 10λ.