Invented by Uri Banin, Hagai Arbell, Bernhard Rieger, Ming-chou Wu, Merck Patent GmbH, Yissum Research Development Co of Hebrew University of Jerusalem
The Merck Patent GmbH, Yissum Research Development Co of Hebrew University of Jerusalem invention works as followsAn optically-active structure and a device for displaying information are presented.” The device used an optically-active structure consisting of liquid crystal material, and a number of nanorods configured emit light within one or more predetermined bands in response to pumping. The liquid crystal’s orientation changes the orientation of the nanorods, modulating the light emitted from them.
Background for LC-based optical Display System
Flat panel display systems are used widely in many devices/systems such as computer monitors and laptops. They can also be found on mobile phones, TV sets, and televisions. In general, flat panel displays have become the most popular display type on the market.
Liquid Crystal (LC), based display system, is a key component of the wide variety of flat-screen display systems. The LC based systems use molecular materials that combine certain liquid properties with a crystal-like arrangement between molecules. Due to the liquid properties, the LC material can be oriented differently in response external fields. Electric field. The LC molecules can be distinguished by their optical properties, such as the birefringence or transmission of polarized light.
LC-based display system use back-illumination units that provide high intensity and uniform lighting on the device’s surface. The LC panel in the display system modulates the uniform back-illumination of the device by blocking or completely blocking light from different areas along the surface. For sufficient modulation, light from the back-illumination is converted into polarized light. The input polarizer is attached to bottom of the LC-cell. Rotation of the LC material changes its transmission to polarized light.
Various types LC based display are known to the art. This includes devices based on LC material with negative dielectric anisotropy, such as those described by U.S. Nos. Nos.
Also, different types of back illumination devices are known. These include units that use optical emission from nanoparticles. Nano-dots or nanoparticles in rod shape. U.S. Pat. describes, for example, optical display devices and illumination units. No. No. 8,471,969 and US Patent Publications 2013/181,234 & 2014/009/902, which are all assigned to the assignee. These nanoparticles-based lighting units can provide high intensity illumination at a desired colour temperature while reducing energy costs and, in some cases, eliminating the need for polarization filters.
The display system can be configured to provide a certain amount of transparency for light coming from the back. Transparent organic LED (TOLED), reflective head-up display, thick blue sheet display and transparent LCD are some of the technologies that provide at least a partially transparent display. These techniques allow the user to see the backside of the display while still allowing light to pass through.
For example US 2014/0292839 provides a transparent display device including a liquid crystal panel. The liquid crystal panel consists of a color filter, an array substrate and a liquid-crystal layer. It also includes a first and second polarizer. The first polarizer lies on the side of the color-filter substrate that is farthest from the liquid crystal. The second polarizer can be disposed on the side of the array substrate that is farthest from the liquid-crystal layer. The color filter substrate consists of a transparent layer and a colored filter. The color filter has compound pixel areas, each of which includes a color sub-pixel area and a transparency sub-pixel. The second polarizer has a nonpolarized pattern that corresponds spatially to the transparent subpixel region of the color filter. After a light passes through the nonpolarized pattern, polarization remains unchanged.
As indicated above, LC based display devices typically use the variation in optical transmission to modulate illumination (i.e. Display an image. The image displayed on a display is created by blocking or partially blocking light transmission in different regions/pixels. These transmission blocking display techniques are energy inefficient because they require high intensity back lighting.
The conventional configuration of partially transparent or transparent display systems has limitations, such as low contrast, brightness and limited viewing angles. It is also difficult to scale up the display size. The present invention uses optically active nanoparticles (in particular nanorods) and their optical emission to create a transparent display system that can provide high brightness, while still maintaining the transparency of the system. The display should transmit at least 15%, preferably 30%, and even more preferably, 40% of the visible light that passes through it. In the art, a novel display device configuration is needed. The present invention is a layer/structure that can be used in display devices. The optically-active structure can allow the display device perform at a higher energy efficiency. The optically active structures of the invention also allow for the design of optically-transparent display systems. The optically-active structure of the invention includes one or more layers with a plurality optically active rod shaped nanoparticles embedded in a molecular liquid crystal matrix (LC). The rod-shaped particles are aligned preferably with the LC matrix such that the orientation variations of the LC molecule cause rotation/shifting together with the nanoparticles.
The optically active rod nanoparticles absorb light in a first wavelength range, typically between UVA (320-400nm) and violet (380-450nm), emitting light within one or more subsequent wavelength ranges. The wavelengths for the second range of wavelengths are determined by the size, shape and composition of the nanoparticles. The material composition of nanoparticles is also used to determine the absorption of first wavelength range light. In some embodiments, nanoparticles that are anisotropic, i.e. One axis is longer than the other. According to certain preferred embodiments, nanoparticles can also be selected as rod-shaped nanoparticles of semiconductors. These rod-shaped particles (also known as nanorods), may have a core-shell, a core-double-shell or a core-multi-shell structural design, wherein the core is made of ONE material composition, and the shells of another material composition. The core may also be made of a single-material core, core-shell, or core-multishell, and it may have an anisotropic or non-anisotropic shape.
In response to pumping energy, nanorods generally emit dipole-like light. Nanorods also provide optical emission that has a relatively high polarization (PR) ratio. In this context, polarization is defined as the ratio of light intensity with parallel and perpendicular orientations relative to the alignment axis of nanorods. The nanorods, when pumped appropriately, emit light in a wavelength range determined by the nanorods parameters. This light is propagated in directions that are perpendicular the the nanorods long axis. The light emitted from the nanorods also has a linear polarization. The polarization ratio may be higher than 1.5 or, preferably, greater than 4. The polarization ratio (PR) may be higher than 1.5, or preferably greater than 4.
The LC layer in which the embedded nanorods are located is designed to change the orientation of LC molecules as a response to an external field. Generally, the LC is configured to respond to an external electric field (either direct current (DC), or alternating field (AC)) by varying the orientation of the LC molecule. In some embodiments, the LC molecules are configured to be aligned parallel to the surface of the layer in one orientation (planar orientation) and aligned vertical to the surface of the layer in a second orientation (vertical/homeotropic orientation). Rotation of the LC materials is preferably configured also to vary the orientation of the embedded nanorods. This rotation may have an effect on the absorption of pumping energy and/or one or more properties emitted by the nanorods, as described further below.
As described above, in some embodiments the present invention is a display system with an optically active structure that can be configured and operated to respond to pumping energy input (e.g. Pumping light) to emit structured light from the device in response to operational commands received from a controller. In certain embodiments, a display system can be configured to at least partially transmit visible light. Display devices are typically designed to change the light they emit to produce one or more images with predetermined presentation times (e.g. a video display).
The present invention, in its broadest aspect, provides an optically-active structure that comprises at least one liquid crystal layer and a plurality optically-active nanorods mixed within the at least one liquid crystal layer. In one orientation, the nanorods emit light in one or more second wavelength ranges predetermined at a high intensity in response to input radiation from a pumping wavelength of the first range, and in a different orientation, the nanorods emit light in a lower intensity in response to the pumping wavelength.
The optically active nanorods can be selected based on their material composition and geometry, which emit light in the second wavelength range.
The liquid crystal material can be configured to change its orientation in response to an external electric field. The liquid crystal material is preferably configured to rotate the axis alignment of said optically-active nanorods in response to the change in orientation. This will alter the properties of light that are absorbed and emitted by the nanorods. The liquid crystal material can be oriented differently to produce a continuous change in the emission of light.
In general, the liquid-crystal material in the optically-active nanorods can be aligned with a predetermined parallel axis to the surface in one orientation state. Then the orientation of the nanorods can be changed to align along a perpendicular axis to the surface in another orientation. In certain embodiments, liquid crystal material can be configured with negative anisotropy.
The nanorod material can be configured or selected to change its emission properties as a response to an external electric field. In the presence of an electric field, the applied field could cause the nanorod to emit less light. The nanorods material should be selected so that external electric fields do not substantially change the wavelength of light emission. This is to prevent color variations when emission intensity is decreased.
The optically-active structure may also include an electrode arrangement consisting of a number of electrode elements that define a number of independently operable pixels in the structure. Said electrode elements are configured to apply a selective electric field to the corresponding pixels, thereby causing rotation of the liquid cristal material and optically-active nanorods.
The optically-active structure can be composed of optically-active nanorods with different types, each having a material composition and dimension that is selected to produce optical emission at a wavelength range distinct from the wavelength ranges of the nanorods in other types. The optically-active nanorods may be arranged in a number of pixel regions to enable color image formation through selective spatial and time variation of the emitted light. Red, green and blue pixels regions and/or pixel areas emitting white lights of desired illumination temperatures.
Click here to view the patent on Google Patents.