METHOD AND ARRANGEMENT FOR INFLUENCING LIGHT PROPAGATION DIRECTIONS

Abstract

A method for influencing light propagation directions of a light-emitting surface emitting light of a first wavelength range in a first direction and light of a second and wavelength range in a second direction. The wavelength ranges have a wavelength-dependent spectral radiance and differ in a peak wavelength. A switchable color converter is arranged in front of the light-emitting surface. The method includes the steps of a) deactivating the color converter for a first mode so that the second-wavelength range is transmitted and the first-wavelength range is absorbed, such that light from the light-emitting surface is only perceptible from the second direction, or b) activating the color converter for a second mode so that light of the first-wavelength range is converted into light of the second-wavelength range and light of the second-wavelength range is transmitted, such that light from the light-emitting surface is perceptible from both directions.

Claims

1. A method for influencing the light propagation directions of at least one light-emitting surface, wherein the light-emitting surface emits light of a first wavelength range in a first spatial direction and light of a wavelength range at least partially differing from the first wavelength range in a spatial direction differing from the first spatial direction, wherein the first and second wavelength ranges have a wavelength-dependent spectral radiance and differ at least in a peak wavelength, and wherein at least one switchable color converter which, in the deactivated state, absorbs light of shorter wavelengths and at the same time transmits light of longer wavelengths and which, in an activated state, converts light of shorter wavelengths into light of longer wavelengths and transmits light of longer wavelengths, and is arranged in front of the light-emitting surface with reference to a viewing direction, the method comprising the following steps: deactivating the color converter for a first mode so that light of the second wavelength range is transmitted and light of the first wavelength range is absorbed, such that the light emanating from the light-emitting surface is only perceptible from the second spatial direction, or activating the color converter for a second mode so that light of the first wavelength range is converted into light of the second wavelength range and light of the second wavelength range is transmitted, such that the light emanating from the light-emitting surface is perceptible from both the first and the second spatial directions.

2. The method according to claim 1, wherein the switchable color converter is formed by quantum dots, wherein each quantum dot has a spatial extent of a maximum of 100 nm.

3. The method according to claim 1, wherein the switchable color converter does not cover the entire light-emitting surface but rather only a subarea thereof.

4. The method according to claim 1, wherein the switchable color converter is deactivated in the presence of an electric field and activated in the absence of an electric field.

5. The method according to claim 1, wherein there is a multitude of self-luminous light-emitting surfaces, each of which corresponds to an emitting surface of a smallest pixel of a QLED display, OLED display, mini-LED display, LED display or micro-LED display, which smallest pixel is formed as a layer body.

6. The method according to claim 5, wherein, in the layer body of the smallest pixel there is at least one electro-optical component which changes an emitting characteristic of the light-emitting surface, by varying a resonance condition in the layer body, and which is formed as a distributed Bragg reflector (DBR), semitransparent mirror, waveplate, liquid crystal layer, electrochromic layer, electrowetting element, switchable absorber or as phase-change material so that, at least in the first spatial direction, light of the first wavelength range is emitted instead of light of the second wavelength range.

7. A method for influencing the light propagation directions of at least one self-luminous or illuminated light-emitting surface, wherein: in a first mode, the light-emitting surface selectively emits light of a first wavelength range in a first spatial direction and light of a second wavelength range at least partially differing from the first wavelength range in a second spatial direction differing from the first spatial direction, or, in a second mode, emits light at least of the second wavelength range in both the first and second spatial directions, wherein the first and second wavelength ranges have a wavelength-dependent spectral radiance and differ at least in a peak wavelength, and wherein at least one color filter which absorbs light of the first wavelength range and transmits light of the second wavelength range is arranged in front of the light-emitting surface with reference to a viewing direction, this method comprising the following steps: activating the first mode, wherein light of the second wavelength range, after passing through the color filter, is only perceptible from the second spatial direction, or activating the second mode, wherein light of the second wavelength range, after passing through the color filter, is perceptible from both the first and second spatial directions.

8. The method according to claim 7, wherein there is a multitude of self-luminous light-emitting surfaces, each of which corresponds to an emitting surface of a smallest pixel of a QLED display, OLED display, mini-LED display, LED display or micro-LED display, which smallest pixel is formed as a layer body.

9. The method according to claim 8, wherein in a layer body of each light-emitting surface arranged under the light-emitting surface, there is an electro-optical component which varies a resonance condition in the layer body and which is formed as a DBR (distributed Bragg reflector), semitransparent mirror, waveplate, liquid crystal layer, electrochromic layer, electrowetting element, switchable absorber or as phase-change material, so that switching can be carried out between the emission of light of the first wavelength range and of the second wavelength range in the first spatial direction.

10. The method according to claim 1, wherein there is at least one pair of inner wavelength ranges within the first wavelength range and the second wavelength range for each of three primary colors red, green and blue for a full-color display, wherein for each pair of inner wavelength ranges, of two peaks in the spectrum which are separated by some nanometers to 200 nm, one peak lies in the first wavelength range and one peak lies in the second wavelength range.

11. An application of a method according to claim 1 for generating a first operating state for a restricted viewing mode and a second operating state for a public viewing mode in a display screen whose smallest pixels have electro-optical components and light-emitting surfaces, wherein the switchable color converter is deactivated for generating the first operating mode and is activated for generating the second operating mode.

12. An arrangement for influencing light propagation directions of at least one light-emitting surface, wherein the light-emitting surface emits light of a first wavelength range in a first spatial direction and light of a second wavelength range at least partially differing from the first wavelength range in a second spatial direction differing from the first spatial direction, wherein the first and second wavelength ranges have a wavelength-dependent spectral radiance and differ at least in a peak wavelength, further comprising at least one switchable color converter which, in a deactivated state, absorbs light of shorter wavelengths and at the same time transmits light of longer wavelengths and which, in an activated state, converts light of shorter wavelengths into light of longer wavelengths and transmits light of longer wavelengths, and is arranged in front of the light-emitting surface with reference to a viewing direction, wherein: the color converter is deactivated for a first mode so that light of the second wavelength range is transmitted and light of the first wavelength range is absorbed, such that the light emanating from the light-emitting surface is only perceptible from the second viewing direction, and the color converter is activated for a second mode so that light of the first wavelength range is at least partially converted into light of the second wavelength range and light of the second wavelength range is transmitted, such that the light emanating from the light-emitting surface is perceptible from both the first and second spatial directions.

13. The arrangement according to claim 12, wherein the switchable color convertor comprises quantum dots.

14. An arrangement for influencing the light propagation directions of at least one light-emitting surface, wherein in a first mode, the light-emitting surface selectively emits light of a first wavelength range in a first spatial direction and light of a second wavelength range at least partially differing from the first wavelength range in a second spatial direction differing from the first spatial direction, or, in a second mode, emits light at least of the second wavelength range in both the first and second spatial directions, wherein the first and second wavelength ranges have a wavelength-dependent spectral radiance and differ at least in a peak wavelength, further comprising at least one color filter which is arranged in front of the light-emitting surface with respect to a viewing direction and which absorbs light of the first wavelength range and transmits light of the second wavelength range, wherein: the first mode is activated, wherein light of the second wavelength range, after passing through the color filter, is perceptible only from the second spatial direction, or the second mode is activated, wherein light of the second wavelength range, after passing through the color filter, is perceptible from both the first and second spatial directions.

15. The arrangement according to claim 14, wherein there is a multitude of self-luminous light-emitting surfaces, each of which corresponds to an emitting surface of a smallest pixel of a QLED display, OLED display, mini-LED display, LED display or micro-LED display, which smallest pixel is formed as layer body.

16. The arrangement according to claim 15, wherein, in a layer body of each light-emitting surface arranged under the light-emitting surface F, there is an electro-optical component which varies the resonance condition in the aforementioned layer body.

17. The method of claim 2, wherein each quantum dot has a spatial extent of a maximum of 50 nm.

18. The method of claim 2, wherein each quantum dot has a spatial extent of a maximum of 20 nm.

19. The arrangement according to claim 16, wherein the electro-optical component is formed as a DBR (distributed Bragg reflector), semitransparent mirror, waveplate, liquid crystal layer, electrochromic layer, electrowetting element, switchable absorber or as phase-change material so that so that emission of light of the first wavelength range can be switched on and off.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The invention will be explained in more detail in the following with reference to drawings which also disclose key features of the invention. The drawings show:

[0049] FIG. 1 the schematic diagram of the construction of a prior art OLED pixel;

[0050] FIG. 2 the schematic diagram of a first embodiment of the method according to the invention;

[0051] FIG. 3 the schematic diagram illustrating the manner of operation of the first embodiment of the method according to the invention shown in FIG. 2;

[0052] FIG. 4 the schematic diagram of a modification of the first embodiment of the method according to the invention shown in FIG. 2;

[0053] FIG. 5 the schematic diagram of a second embodiment of the method according to the invention;

[0054] FIG. 6 the schematic diagram illustrating the manner of operation of the second embodiment of the method according to the invention shown in FIG. 5;

[0055] FIG. 7 the schematic diagram of a third embodiment of the method according to the invention; and

[0056] FIG. 8 an exemplary diagram for exemplary wavelength ranges Δλ.sub.1 and Δλ.sub.2.

DETAILED DESCRIPTION OF THE DRAWINGS

[0057] The drawings are not to scale and are merely schematic depictions.

[0058] FIG. 1 shows the schematic diagram of the construction of the layer body of a prior art OLED pixel. Located below a transparent substrate 1 (e.g., of glass or a polymer) in viewing direction is a semitransparent first electrode 2, for example, an anode, an organic layer 3 followed by an emissive layer 4 and, under the latter, another organic layer 5 and, finally, a mirror with a second electrode 6, for example, a cathode. In general, the organic layers 3 and 5 in the layer body in particular can be appreciably more complex. This embodiment with (at least) one OLED pixel as (self-luminous) light-emitting surface F makes use of the fact that light from OLEDs toward lateral emitting angles has a shorter wavelength than perpendicularly emitted light.

[0059] Further, FIG. 2 shows the schematic diagram of a first embodiment of the method according to the invention which is based on the OLED construction according to FIG. 1. The method according to the invention for influencing the light propagation directions of at least one self-luminous or illuminated light-emitting surface F, which light-emitting surface F emits light of a first wavelength range Δλ.sub.1 in a first spatial direction R1 and light of a wavelength range Δλ.sub.2 at least partially differing from the first wavelength range Δλ.sub.1 in a spatial direction R2 differing from the first spatial direction R1, and the wavelength ranges Δλ.sub.1 and Δλ.sub.2 have a wavelength-dependent spectral radiance and differ (but otherwise can also partially overlap) at least in a peak wavelength, and a switchable color converter 7 which, in the deactivated state, absorbs light of shorter wavelengths and at the same time transmits light of longer wavelengths and which, in the activated state, converts light of shorter wavelength into light of longer wavelengths and transmits light of longer wavelengths is arranged in front of the aforementioned light-emitting surface F with reference to viewing direction, the method comprising the following steps: [0060] deactivating the color converter 7 for a first mode so that light of the second wavelength range Δλ.sub.2 is transmitted and light of the first wavelength range Δλ.sub.1 is absorbed, by means of which the light emanating from the light-emitting surface F is only perceptible from the second viewing direction R2, or [0061] activating the color converter 7 for a second mode so that light of the first wavelength range Δλ.sub.1 is at least partially converted into light of the second wavelength range Δλ.sub.2 and light of the second wavelength range Δλ.sub.2 is transmitted, by means of which the light emanating from the light-emitting surface F is perceptible from both spatial directions R1, R2.

[0062] It should also be noted, without limiting generality, that the first wavelength range Δλ.sub.1 is emitted in the first spatial direction R1 and the second wavelength range Δλ.sub.2 is emitted in the second spatial direction R2. This association shall also apply in the following embodiments of the invention. It will be appreciated that the two spatial directions R1 and R2 could also be interchanged without departing from the scope of the invention.

[0063] The light-emitting surface F is represented by a bold black line (as sectional view) in FIG. 2. In reality, however, it has a surface area of a few square micrometers to, typically, some square millimeters. The light-emitting surface F is oriented perpendicular to the drawing plane of the schematic diagram.

[0064] The schematic diagram illustrating the manner of operation of the first embodiment of the method according to the invention is shown in FIG. 3.

[0065] The color converter 7 is deactivated for the first mode (right-hand side) so that light of the second wavelength range Δλ.sub.2 (denoted here by “R” for light with longer wavelength on average, for example, usually red light) is transmitted and light of the first wavelength range Δλ.sub.1 (denoted here by “B” for light with shorter wavelength on average, for example, usually blue light) is absorbed, as a result of which the light proceeding from the light-emitting surface F is only perceptible from the (restricted) second spatial direction R2.

[0066] In contrast, the color converter 7 is activated for the second mode (left-hand side in FIG. 3) so that light of the first wavelength range Δλ.sub.1 is converted into light of the second wavelength range Δλ.sub.2 and light of the second wavelength range Δλ.sub.2 is transmitted, as a result of which the light emanating from the light-emitting surface F is perceptible from both spatial directions R1, R2.

[0067] The switchable color converter 7 can preferably be formed by means of quantum dots. There is a multitude of quantum dots for each color converter. Each quantum dot can have, for example, a spatial extent of a maximum of 100 nm, preferably a maximum of 50 nm, particularly preferably a maximum of 20 nm. The switchable color converter 7 need not necessarily be connected with the substrate 1.

[0068] Of course, “spatial direction” R1 or R2 means a solid angle spreading out in one or two planes and comprising a few to some degrees in each plane. It is also possible that, e.g., a spatial direction R1 is outwardly cone-shaped, a second conical shape being cut out inside of this cone, for example, that of a second spatial direction R2, so that both spatial directions R1 and R2 together give a total conical shape. Correspondingly, a plurality of spatial directions together give a larger solid angle. The fact that the spatial directions R1 and R2 differ need not mean that they can also have a certain overlap. However, in the area of the overlap, the method described above does not afford an extensive influence on the propagation directions of the light emitted by the light-emitting surface F.

[0069] Semiconductor nanocrystals, for example, are contemplated as materials for the quantum dots, such as: CdSe, CdS, CdTe, ZnSe, ZnTe, ZnS, HgTe, InAs, InP, GaAs, GaP, GaInP 2, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeT, CdZn CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSeS, HgZnSeSe, HgZnSeS, GaN, AlN, AlP, AlAs, InN, InP, InAs, GaNP, GaNAs, GaPAs, AlNP, AlNAs,AlPAs,InNP, InNAs, InPAs, GaAlNP, GaAlNAs, GaAlPAs, , GaInPAs, InAlNP, InAlNAs, and/or InAlPAs. It is also possible to use other types of quantum dots, e.g., graphenes, synthetic perovskites or silicon.

[0070] It may be helpful for particular configurations that the switchable color converter 7 does not cover the entire self-luminous or illuminated light-emitting surface F but rather only a strict subarea thereof. This is shown in FIG. 4. Here the color converter 7 only partially overlaps the light-emitting surface F, namely at the edges. The color converter 7 is used for obliquely exiting light, but not for perpendicularly exiting light.

[0071] It is advantageous when the switchable color converter 7 is deactivated in the presence of an electric field and activated in the absence of an electric field.

[0072] Further, there is preferably provided a multitude of self-luminous light-emitting surfaces F, each of which corresponds to a smallest pixel of a QLED display, OLED display, mini-LED display, LED display or micro-LED display. Smallest pixels can be color subpixels (e.g., red, green, blue) or monochromatic pixels or full-color enabled pixels depending on the construction of the imaging device. Also contemplated are LCD-type, SED-type, FED-type or other types of display screen whose smallest pixels correspond to the multitude of illuminated or self-luminous light-emitting surfaces F.

[0073] Beyond this, it is possible that a distributed Bragg reflector (DBR) 9, a semitransparent mirror, additional emission layers and/or a waveplate are provided in the layer body of a smallest pixel of this kind so that, at least in the first spatial direction R1, light of the first wavelength range Δλ.sub.1 is emitted instead of light of the second wavelength range Δλ.sub.2. An additional element of this kind can also be switchable. A switchable DBR can be realized, for example, by means of liquid crystals or a phase-change material. It is important in this respect that the light of the second wavelength range Δλ.sub.2 is collimated, i.e., limited to certain propagation directions R2.

[0074] Further, FIG. 5 shows the schematic diagram of a second embodiment of the method according to the invention. In this case, in a first mode, the aforementioned light-emitting surface F selectively emits light of a first wavelength range Δλ.sub.1 in a first spatial direction R1 and light of a second wavelength range Δλ.sub.2 at least partially differing from the first wavelength range Δλ.sub.1 in a second spatial direction R2 differing from the first spatial direction, or, in a second mode, emits light at least of the second wavelength range Δλ.sub.2 in both spatial directions R1, R2, the wavelength ranges Δλ.sub.1 and Δλ.sub.2 have a wavelength-dependent spectral radiance and differ (but otherwise can also partially overlap) at least in a peak wavelength or their peak wavelengths, and at least one color filter 8 which absorbs light of wavelength range Δλ.sub.1 and transmits light of the wavelength range is arranged in front of the aforementioned light-emitting surface F with reference to viewing direction. In a particularly preferable manner, the light of wavelength range Δλ.sub.2 is collimated in the first mode and not collimated in the second mode.

[0075] Proceeding therefrom, the second embodiment of the method according to the invention comprises the following steps: [0076] activating the first mode in which light of the second wavelength range Δλ.sub.2 after passing the color filter 8 is only perceptible from the second spatial direction R2, or [0077] activating the second mode in which light of the second wavelength range Δλ.sub.2 after passing the color filter 8 is perceptible from both spatial directions R1, R2.

[0078] This manner of operation of the second embodiment of the method according to the invention is shown as schematic diagram in FIG. 6. When the first mode is activated (right-hand side in the drawing), light of the second wavelength range Δλ.sub.2 (denoted here by “R” for light with longer wavelength on average) is transmitted and light of the first wavelength range Δλ.sub.1 (denoted here by “B” for light with shorter wavelength on average) is absorbed, as a result of which the light emanating from the light-emitting surface F is perceptible after passing through the color filter 8 only from one spatial direction R2. On the other hand, if the second mode is activated so that light of the second wavelength range Δλ.sub.2 is transmitted, the light emanating from the light-emitting surface F is perceptible from spatial directions R1, R2 after passing through the color filter 8 as is shown on the left-hand side in the drawing.

[0079] Further, a switchable DBR 9 (distributed Bragg reflector), a switchable mirror and/or a switchable waveplate can be provided in the layer body of every self-luminous or illuminated light-emitting surface F in the above-mentioned method variant according to FIG. 5 so that the emission of light of the first wavelength range Δλ.sub.1 can be switched on and off.

[0080] The invention acquires special significance in the application of the above-described method for generating a first operating state B1 for a restricted viewing mode and a second operating state B2 for a public viewing mode in a display screen whose smallest pixels correspond to the aforementioned light-emitting surfaces F according to one of the method variants mentioned above, wherein [0081] for the first operating state B1 for a restricted viewing mode, a switchable color converter 7, if provided, is deactivated and/or a DBR (distributed Bragg reflector) 9, a switchable mirror or a waveplate, if provided, is activated, and [0082] for the second operating state B2 for a public viewing mode, a switchable color converter 7, if provided, is activated and/or a DBR (distributed Bragg reflector) 9, a switchable mirror or a waveplate, if provided, is deactivated.

[0083] Further, FIG. 7 shows the schematic diagram of a third embodiment of the method according to the invention. This is a further development of the second embodiment according to FIG. 5 in which the layer body contains various emissive layers 4 for R, G, B (red, green, blue) in order to obtain full color from a luminous light-emitting surface F. Accordingly, the first wavelength range Δλ.sub.1 comprises red, green and blue spectral components. The light propagation direction are influenced in this case via (at least) one color converter 7 arranged in front of the substrate and one color filter 8 for light of shorter wavelength on average, i.e., the first wavelength range Δλ.sub.1. The various emissive layers 4 (R, G, B for red, green and blue, respectively) in combination with the color converter 10 produce these three primary colors in a light-emitting surface F which is self-luminous in this instance.

[0084] In case of the use of full color, described above, two or three or possibly even more such color converters 7 or color filters 8 which are responsible for one or more peak wavelengths can be provided depending on the configuration.

[0085] Finally, FIG. 8 shows an exemplary diagram for exemplary wavelength ranges Δλ.sub.2 and Δλ.sub.1. It should be noted here once again that the wavelength ranges Δλ.sub.2 and Δλ.sub.1 can certainly have more wavelength peaks, although they must be pairwise disjoint.

[0086] The drawings described above can also be made use of in an analogous manner to illustrate the arrangements according to the invention which will not be described here in order to avoid redundancy.

[0087] The method according to the invention described above meets the above-stated object. A method and arrangement for influencing light propagation directions are described. The invention is particularly applicable to OLED pixels or OLED display screens and is capable of making possible operating modes for public view and restricted view. Further, the invention is inexpensively implementable and universally usable particularly with diverse types of display screen in order to make it possible to switch between a private viewing mode and a public viewing mode in such a way that the resolution of such a display screen is not significantly reduced.

[0088] The invention described above can advantageously be used in cooperation with an image display device anywhere that confidential data are displayed and/or entered, such as when entering a PIN number or displaying data on automatic teller machines or payment terminals or for entering passwords or when reading emails on mobile devices. The invention can also be applied in passenger cars when the driver’s attention should not be drawn to distracting images. Further cases of application lie within the field of lighting and advertisement, in particular for preventing light pollution.

LIST OF REFERENCE CHARACTERS

[0089] 1 substrate [0090] 2 semitransparent first electrode [0091] 3 organic layer [0092] 4 emissive layer [0093] 5 organic layer [0094] 6 mirror and electrode or reflective second electrode [0095] 7 color converter [0096] 8 color filter [0097] 9 DBR (distributed Bragg reflector) [0098] 10 color converter [0099] F light-emitting surface