Device having spacers

1. An electroluminescent device comprising:

a substrate;

one or more light-emitting elements formed over the substrate, the one or more light-emitting elements including first and second spaced-apart electrodes wherein at least one of the first and second electrodes is transparent and a light-emitting layer comprising quantum dots formed between the first and second electrodes;

a cover located over the one or more light-emitting elements and spaced apart from the one or more light-emitting elements to form a gap between the cover and the one or more light-emitting elements; and

separately formed elastic compressible spacer elements located in the gap between the cover and the one or more light-emitting elements and wherein the spacer elements are in physical contact with the one or more light-emitting elements, the cover, or both the one or more light-emitting elements and the cover.

2. The electroluminescent device of claim 1 , wherein the light-emitting layer is a polycrystalline inorganic light-emitting layer comprising core/shell quantum dots within an inorganic semiconductor matrix.

3. The electroluminescent device of claim 1 , wherein the light-emitting layer is a hybrid light-emitting layer comprising core/shell quantum dots within an organic semiconductor matrix.

4. The electroluminescent device of claim 1 , wherein the first electrode lies over the substrate, the light-emitting layer lies over the first electrode on the side of the first electrode opposite the substrate, and the second electrode is the transparent electrode and lies over the light-emitting layer on the side of the light-emitting layer opposite the first electrode.

5. The electroluminescent device of claim 1 , wherein further comprising light-scattering particles located on the transparent electrode on the side of the transparent electrode opposite the light-emitting layer.

6. The electroluminescent device of claim 1 , wherein at least one of the electrodes is a patterned electrode defining independently controlled, spatially separated, light-emitting areas.

7. The electroluminescent device of claim 6 , wherein the spacer elements are located in the light-emitting areas.

8. The electroluminescent device of claim 6 , wherein the spacer elements are located between the light-emitting areas.

9. The electroluminescent device of claim 1 , wherein the gap is maintained at a pressure of less than one atmosphere.

10. The electroluminescent device of claim 1 , wherein the gap has an optical index lower than the optical index of any of the components of the one or more light-emitting elements.

11. The electroluminescent device of claim 1 , wherein the spacer elements are selected from the group of titanium dioxide, polymer, barium oxide, calcium, and calcium oxide.

12. The electroluminescent device of claim 1 , wherein the spacer elements are transparent.

13. The electroluminescent device of claim 1 , wherein the spacer elements are affixed to the cover or to one or more light-emitting elements with an adhesive.

14. The electroluminescent device of claim 13 , wherein the adhesive is patterned.

15. The electroluminescent device of claim 1 , wherein the spacer elements are spherical, cylindrical, or randomly shaped particles.

16. The electroluminescent device of claim 1 , wherein the spacer elements have a refractive index greater than the refractive index of any component of the light-emitting element

17. An electroluminescent device comprising:

a substrate;

one or more light-emitting elements formed over the substrate, the one or more light-emitting elements including first and second spaced-apart electrodes wherein at least one of the first and second electrodes is transparent and a light-emitting layer comprising quantum dots formed between the first and second electrodes;

a cover located over the one or more light-emitting elements and spaced apart from the one or more light-emitting elements to form a gap between the cover and the one or more light-emitting elements; and

separately formed spacer elements located in the gap between the cover and the one or more light-emitting elements and wherein the spacer elements are in physical contact with the one or more light-emitting elements, the cover, or both the one or more light-emitting elements and the cover, wherein the separately formed spacer elements have a first average size and wherein the device further comprises separately formed light-scattering particles, wherein the light-scattering particles have a second average size smaller than the first average size, and are located in the gap, in contact with the one or more light-emitting elements and located between the spacer elements.

18. The electroluminescent device of claim 17 , wherein the light-scattering particles and the spacer elements are deposited from a common dispersion.

19. An electroluminescent device comprising:

a substrate;

one or more light-emitting elements formed over the substrate, the one or more light-emitting elements including first and second spaced-apart electrodes wherein at least one of the first and second electrodes is transparent and a light-emitting layer comprising quantum dots formed between the first and second electrodes;

a cover located over the one or more light-emitting elements and spaced apart from the one or more light-emitting elements to form a gap between the cover and the one or more light-emitting elements; and

separately formed spacer elements having a cross section greater than 1 micron located in the gap between the cover and the one or more light-emitting elements and wherein the spacer elements are in physical contact with the one or more light-emitting elements, the cover, or both the one or more light-emitting elements and the cover.