EP2179323A1

EP2179323A1 - Lcd backlighting with led phosphors

Info

Publication number: EP2179323A1
Application number: EP08774036A
Authority: EP
Inventors: Holger Winkler; Thomas Juestel
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2007-08-20
Filing date: 2008-07-23
Publication date: 2010-04-28
Also published as: KR20100074142A; TW200925742A; US20110299008A1; JP2010537375A; DE102007039260A1; CN101784948A; WO2009024229A9; WO2009024229A1

Abstract

The invention relates to a liquid crystal display equipped with a backlighting system with a white light source, which contains a semiconductor diode and a phosphor layer consisting of a combination of at least two phosphors, wherein at least one phosphor emits red light and at least one phosphor emits green light, and a production process therefor.

Description

LCD backlight with LED phosphors

The invention relates to a liquid crystal display with a background lighting system with a white light source, which comprises a semiconductor diode and a phosphor layer of a combination of at least two

Contains phosphors, wherein at least one phosphor emits red and at least one phosphor green light. Furthermore, the invention relates to a backlight system and its manufacturing method.

Liquid crystal displays (LCDs) are passive display systems, i. they do not shine themselves. These indications are based on the principle that light passes or does not pass through the layer of liquid crystals. This means that an external light source is needed to create an image. In reflective liquid crystal displays, the ambient light is used as an external light source, so they basically do without backlighting. In transmissive liquid crystal displays, light is generated in a backlight system. In the meantime, transflective liquid crystal displays (transmissive and reflective at the same time) play a major role, in which a transflector is usually located behind the polarizer facing away from the observer. Each pixel is subdivided into a reflective and a transmissive subpixel whose associated liquid crystal layer thicknesses are approximately in the ratio 1: 2. The reflective part operates with ambient light and has a reflective substrate layer, e.g. made of aluminium. The transmissive part behaves e.g. like a TN-ZeIIe (= twisted nematic) and can be switched by switchable

Backlight especially in poor outdoor lighting conditions to realize the necessary contrast. The latter come nowadays, e.g. in PDAs, games (Game Boys), viewfinder for digital cameras or even in (cheap) notebooks are used because they u.a. are energy efficient.

In liquid crystal displays, primary colors of the pixels can be generated by using white light from the backlight with the help of filtered by color filters eg into the primary colors blue, green and red. The color gamut, which is important for the color representation, which the display can produce is limited by the purity of the blue, green and red primary colors. Transferred to a CIE xy color chart, the red, green and blue primary colors of the display span a triangle indicating the color space that can be displayed by the display. Colors outside this color space can not be displayed by the display.

In liquid crystal displays, the color space is determined by several factors:

For one, this is the backlight source and the LCD panel itself: each pixel of the screen consists of red, green, and blue areas. The colors of these areas are generated by the transmission of the white light of the backlight through a color filter array. The color filters are partly responsible for the color space of the display.

Commonly used for LCDs are broadband emitting light sources for backlighting, such as CCFLs (CoId Cathode Fluorescent Lamps) or xenon discharge lamps, which emit a wide range of colors with levels of unwanted color, such as light emitting diodes. As orange, yellow and cyan. To maximize the displayable color space of the screen only pure red, green and blue are needed. The primary colors must be saturated because the white light of the primary light source is broken down into the primary colors by the color filters.

In this case, to increase the color space, it is necessary to convert the light of the backlight into a spectrum of narrower bands of blue, green and red portions by using additional color filters. In addition to the technical complexity of such additional color filtering while the luminous flux is greatly reduced, causing the

Brightness of the screen is reduced. To circumvent these disadvantages of the broadband backlight. The CCFLs leading to a limited color space and the necessary additional complex color filters for reduced screen brightness have therefore recently been substituted by LED arrays. These arrays consist of blue, green and red LEDs that emit a much narrower band compared to CCFLs. For this reason, the displayable color space of the display is larger and the achievable brightness higher because only simple color filters are needed. Other advantages that result are the higher energy efficiency of the display, because the backlight transmittance is significantly higher for LEDs (70%) than for CCFLs (5%). Furthermore, LED backlights have a significantly longer life than CCFLs (100,000 operating hours for LEDs vs. 5000 operating hours for CCFLs), and LEDs do not use mercury, which is essential in CCFLs.

However, the disadvantage of using backlit blue, green and red LEDs is that the semiconductor chips of LEDs are different: InGaN for blue light, InGaN for green light (but with higher In content) and red Light is used in InGaAIP as a material basis. These three materials show different efficiencies for the emission of light and exhibit different degradation behaviors. As a consequence, an elaborate active control must be used which keeps the color point of the white light composed of the blue, green and red LEDs constant via control circuits which intervene in the LED control.

This sophisticated active control for each individual backlight LED (up to several 1000 LEDs) results in such high costs that LCD TVs equipped with them are 4 to 10 times more expensive than CCFL-equipped displays.

The high price prevents the market penetration of the qualitatively much better LED backlight. WO 02/095791 describes a liquid crystal panel equipped with a gas discharge lamp (cold cathode lamp or Xe discharge lamp) as a white light source containing a phosphor layer with a combination of phosphors emitting red, green and blue light.

The object of the present invention was to provide a backlight system which has the same high quality

(in terms of displayable color space and brightness) as a R, G, B-LED backlight has, but this at a much lower cost.

It has now surprisingly been found that the use of certain LEDs on the use of the complex active control of each LED can be dispensed with and these LEDs can be used in conventional backlight systems. These LEDs according to the invention allow less expensive backlighting, which is calculated over the life of the screen, with lower costs than a conventional CCFL backlight.

The present invention thus provides a liquid crystal display equipped with at least one backlight system having at least one white light source, which contains at least one semiconductor diode, preferably emitting blue, and at least one phosphor layer comprising a combination of at least two phosphors, wherein at least one phosphor is red light and at least one phosphor emits green light. A liquid crystal display usually has a liquid crystal unit and a backlight system. The liquid crystal unit typically comprises a first and a second polarizer and a liquid crystal cell having two transparent layers, each carrying a matrix of light-transmissive electrodes. Between the two substrates, a liquid crystal material is arranged. The liquid crystal material includes, for example, TN (twisted nematic) liquid crystals, super twisted nematic (STN) liquid crystals, double super twisted nematic (DSTN) liquid crystals, foil super twisted nematic (FSTN) liquid crystals, vertically alligned liquid crystals (VAN) or OCB (optically compensated bend) liquid crystals. The liquid crystal cell is sandwiched by the two polarizers, the second polarizer being seen by the viewer. Also very suitable for monitor applications is the I PS technology (In Plane Switching). In contrast to the TN display are in the

IPS ZeIIe the electrodes, in the electric field, the liquid crystal molecules are switched, only on one side of the liquid crystal layer. The resulting electric field is inhomogeneous and aligned in a first approximation parallel to the substrate surface. The molecules are correspondingly switched in the substrate plane (in plane), which in comparison to TN

Display leads to a significantly lower viewing angle dependence of the transmitted intensity.

Another not-so-well-known technique for good optical properties over a wide viewing angle is the FFS and its further development, the AFFS technology (Advanced Fringe Field Switching). It has a similar operating principle to IPS technology.

A further subject of the present invention is a backlight system with a white light source, which contains a semiconductor diode, preferably emitting in the blue, and a phosphor layer comprising a combination of at least two phosphors which emit red and green light. The backlight system according to the invention can be, for example, a "Direct Lif backlight system (see FIG. 1) or a" side lit "backlight system (see FIG. 2), which has a light guide and a coupling-out structure.

The backlight system has a white light source, which is usually located in a housing, which preferably has a reflector on the inside. The backlight system may further include at least one diffuser plate. For generating and displaying colored images, the liquid crystal unit is provided with a color filter. The color filter contains mosaic patterned pixels that pass either red, green, or blue light. The color filter is preferably arranged between the first polarizer and the liquid crystal cell.

The white (primary) light source includes one emitting in the blue indi- umAluminiumGalliumNitrid semiconductor diode, in particular of the formula InjGa- _j Al _k N, where 0 <i, 0 <j, 0 <k, and i + j + k = 1. Preferably, this is an InGaN semiconductor diode which, in conjunction with corresponding conversion luminescent substances, preferably emits white or almost white light.

This InGaN semiconductor diode has an emission maximum between 430 nm and 480 nm and has a very high efficiency and long life (> 150,000 hours) with only a very low degradation of the efficiency.

In a further embodiment, the white light source may also be a luminescent compound based on ZnO, TCO, ZnSe or SiC. Basically, for a blue-emitting semiconductor diode, which in

Combination with a fluorescent layer that produces white light, one Variety of designs possible, which are selected according to the purpose of use.

The white light source according to the invention has a phosphor layer with a combination of red and green emitting phosphors.

A further subject of the present invention is a process for producing a liquid crystal display equipped with a backlight system with a white light source, comprising the following steps: Production of at least one LED, which consists of a blue-emitting InGaAIN semiconductor, in particular of the formula InjGa _j Al _k N, where 0 <i, 0 <j, 0 <k, and i + j + k = 1, and is composed of a phosphor layer containing a combination of a red and green emitting phosphor. • Installation of one or more LEDs in a housing to a backlight system, including diffusers and reflectors. The backlight system is assembled with a corresponding liquid crystal unit containing a front panel with a color filter system for liquid crystal display.

The green-emitting phosphors which are excited by the blue-emitting primary light source have emission maxima between 520 and 550 nm. According to the invention, all cerium (III) or europium (II) -activated phosphors which are selected from the group of thiogallates are preferred , Silicates, oxonitridosilicates, aluminates, nitrides or garnets. Examples of these phosphors are here (Y ₁ Lu) ₃ (Al ₁ Ga) ₅ Oi ₂ : Ce; SrSi ₂ N ₂ O ₂ : Eu; SrGa ₂ S ₄ : Eu; (Sr, Ba) ₂ SiO ₄ : Eu and SrAl ₂ O ₄ : Eu.

These are prepared by conventional methods via solid-state synthesis or wet-chemically (see William M. Yen, Marvin J. Weber, Inorganic Phosphors, Compositions, Preparation and Optical Properties, CRC Press, New York, 2004)

The red emitting phosphors, which are preferably line emitters, are excited either by the blue emitting primary light source or by the green emitting phosphor. The red-emitting phosphors are preferably europium (III) or chromium (III) -activated line emitters. According to the invention, they have either an emission maximum between 590 and 620 nm (in the case of Eu (I I l) -activated phosphors) or a maximum between 680 and 700 nm (in the case of

Cr (III) activated phosphors). The phosphor layer particularly preferably contains, as the red-emitting phosphor, a europium or chromium activated line emitter selected from the group AI ₂ O ₃ : Cr, Nao.5Gdo.3Euo.2WO4, Nao. ₅ Yo.4Euo.iMoθ4, Nao.5Lao.3Euo.2WO4, Nao.5Lao. ₃ Euo.2MoO ₄ , Nao.5La _o . ₃ Euo.2 (WO ₄ ) o.5 (MoO ₄ ) o.5. La-ι.2Eu ₀ .8MoO ₄ ,

La ₁ .2Eu _{0 8} WO ₄ , (Gd ₀ .6Euo.4) 2 (W0 ₄ ) i.5Pθ4.

Al ₂ O ₃ : Cr (ruby) is efficiently excited in the yellowish-green region of the spectrum to emit a deep red line at 693 nm. Eu (III) activated phosphors can be used if a matrix is used which (partially) removes the ban on europium's inner ff absorption transitions.

The inventively preferred red line emitter A ^ O ₃ ICr is wet-chemically produced (see DE 102006054328.9 and DE 102007001903.5).

Thus, these rubies are very inexpensive to produce and are suitable as a conversion phosphor for pcLEDs to produce warm white light with high efficiency and superior color rendering due to deep red emission. These phosphors can be prepared in a wet-chemical process in which 0.01 to 10 wt% of Cr ³⁺ or Cr ₂ O ₃ doped Al ₂ O ₃ particles are obtained, which have an adjustable size and uniform morphology. The educts for producing the phosphor consist of the base material (eg salt solutions of aluminum) and at least one Cr (III) -containing dopant. Suitable starting materials are inorganic and / or organic substances such as nitrates, carbonates, bicarbonates, hydrogen phosphates, phosphates, carboxylates, alcoholates, acetates, oxalates, halides, sulfates, organometallic compounds, hydroxides and / or oxides of the metals, semimetals, transition metals and / or rare earths, which are dissolved and / or suspended in inorganic and / or organic liquids. Preferably, mixed nitrate solutions, chloride or hydroxide solutions are used which contain the corresponding elements in the required stoichiometric ratio. Another advantage of the red emitting phosphor according to the invention is that the brightness of the phosphor increases with increasing temperature. This is surprising since usually the brightness of phosphors decreases with increasing temperature. This advantageous property according to the invention is particularly important when using the phosphor in high power LEDs (> 1 watt power consumption), since these can come to operating temperatures of over 150 ⁰ C.

The wet-chemical preparation generally has the advantage that the resulting materials have a higher uniformity with regard to the stoichiometric composition, the particle size and the morphology of the particles from which the red line emitter according to the invention is produced. The wet-chemical preparation of the phosphor preferably takes place after precipitation and / or solination.

Method.

The preparation of the line emitter according to the invention is carried out by conventional methods from the corresponding metal and / or rare earth salts, preferably from an aluminum sulfate, potassium sulfate, sodium sulfate and chrome alum solution). The production process is described in detail in

EP 763573 described. In this case, phosphors or precursors thereof are applied to the ruby particles in the process conditions known to those skilled in the art. After separation of the suspension, the material is dried and subjected to an annealing process, which can take place up to 1700 ⁰ C in several stages, and (partial) under reduc- ornamental conditions at temperatures.

After several purification steps, the phosphor is annealed for several hours at temperatures between 600 and 1800 ⁰ C, preferably between 800 and 1700 ⁰ C. In this case, the phosphor precursor is converted into the actual phosphor.

It is preferable to carry out the annealing at least partially under reducing conditions (for example with carbon monoxide, forming gas, pure or diluted hydrogen or at least a vacuum or oxygen deficiency atmosphere).

Furthermore, the inventive red line emitter can also be prepared by single-crystal synthesis methods (for example according to the Verneuil method, see Contacts (Merck) 1991, No. 2, 17-32 or Ullmann (4.) 15, 146, Source: CD Römpp Chemie Lexicon - Version 1.0, Stuttgart / New York: Georg Thieme Verlag 1995)

The mentioned methods are used under designations such as Kyropoulus, Bridgman-Stockbarger, Czochralski, Verneuil and hydrothermal synthesis. One differentiates also crucible-free zone melting u. Crucible pulling (Source: CD Römpp Chemie Lexikon - Version 1.0, Stuttgart / New York: Georg Thieme Verlag 1995).

The red emitting line emitter Nao. ₅ Gdo. ₃ Euo.2WO4, Nao. ₅ Yo.4Euo.iMo0 ₄₎ Nao. ₅ Lao. ₃ Euo. ₂ WO ₄ , Nao.sLao. ₃ Euo. ₂ MoO4, Nao.5Lao.3Euo.2 (WO ₄ ) o.5 (Moθ4) o.5. Lai. ₂ Eu _{0 8} MoO ₄ , LaL ₂ Eu ₀ SWO ₄ ,

(Gd _0th ₆ EU _0. ₄₎ 2 (WO ₄₎ i _.5 PO ₄ are preferably wet-chemically prepared, and then thermally treated (see DE 102006027026.6). For the preparation can be used as starting materials nitrates, halides and / or phosphates of the corresponding metals, semimetals, transition metals and / or rare earths.

According to the invention, the dissolved or suspended educts with a surface-active agent, preferably a glycol, more

Hours heated and the resulting intermediate at room temperature with an organic precipitating reagent, preferably acetone, isolated. After the cleaning and drying of the intermediate this is subjected to a thermal treatment for several hours at temperatures between 600 and 1200 ⁰ C, so that the end product of the red

Line emitter phosphor is created.

Both the red and green emitting conversion phosphors, which are the phosphor layer, are chemically stable to degradation during operation of the LED, i. they show no tendency to hydrolysis and no reaction with materials from their environment.

The following examples are intended to illustrate the present invention. However, they are by no means to be considered limiting. All compounds or components that can be used in the formulations are either known and commercially available or can be synthesized by known methods.

Examples

Example 1 Production of Red-emitting Phosphor Particles of the Composition Ali ₉ 9i0 ₃ : Cro.oo9

In 450 ml of deionized water, 223.8 g of aluminum sulfate 18-hydrate, 114.5 g of sodium sulfate, 93.7 g of potassium sulfate and 2.59 g of KCr (SO ₄ ) ₂ x 12H ₂ O. (Chromalaun) dissolved at about 75 ⁰ C. 2.0 g of a 34.4% titanium sulfate solution are added to this mixture, resulting in the aqueous solution (a).

In 250 ml of deionized water are 0.9 g tert. Sodium phosphate 12 hydrate and 107.9 g of sodium carbonate dissolved, from which the aqueous solution

(b) arises.

The two aqueous solutions (a) and (b) are added simultaneously to 200 ml of deionized water while stirring within 15 min. It is stirred for another 15 min. The resulting solution is evaporated to dryness and the resulting solid annealed at about 1200 ⁰ C for 5 h. Water is added to wash out free sulphate. After customary purification steps with water and drying, the desired phosphors Ali.99iO ₃ : Cr ₀ .oo9 are formed.

Example 2: Preparation of the red phosphor Nao. ₅ Gdo. ₃ Euo. ₂ WO ₄

2.708 g of gadolinium nitrate hexahydrate and 1.784 g of europium nitrate hexahydrate are dissolved in 100 ml of ethylene glycol [solution 1]. At the same time, a solution of 1.550 g of sodium tungstate dihydrate in 50 ml of demineralized water is prepared [solution 2]. 40 ml of solution 1 are introduced, to which is added a mixture of 45 ml of solution 2, 45 ml of ethylene glycol and 3 ml of NaOH.

Sol. (1M) dropped. After the dropwise addition (solution has a pH of 7.5), the mixture is refluxed for 6 hours. After cooling the reaction solution, 200 ml of acetone are added dropwise, then the precipitate is removed by centrifuging, washed once more with acetone and dried in a stream of air, transferred to a porcelain dish and calcined at 600 ⁰ C for 5 h.

Example 3: Preparation of the red phosphor NaO ₅ Yo ^ Eu _{0 1} MoO ₄ 3.06 g of yttrium nitrate hexahydrate and 0.892 g of europium nitrate hexahydrate are dissolved in 100 ml of ethylene glycol [solution 1]. At the same time a Solution of 1, 210 g of sodium molybdate dihydrate in 50 ml of deionized water [Solution 2]. 20 ml of solution 1 were initially charged, to which was added a mixture of 45 ml of solution 2, 45 ml of ethylene glycol and 3 ml of NaOH solution. (1M) dropped. After the dropping, the mixture was refluxed for 6 hours.

After cooling the reaction solution, 200 ml of acetone were added dropwise, then the precipitate was removed by centrifuging, washed once more with acetone and dried in a stream of air.

The mixture was transferred to a muffle furnace and calcined there at 600 ⁰ C for 5 hours.

Example 4 Preparation of the Red Phosphorus Na ₀ , ₅ Lao, ₃ Euo, ₂ W0 ₄ (Precipitation Reaction)

2.120 g of lanthanum chloride hexahydrate and 1.467 g of europium chloride hexahydrate are dissolved in 100 ml of demineralized water [solution 1]. At the same time, a solution of 4.948 g of sodium tungstate dihydrate in 100 ml of deionized water is prepared [solution 2]. 100 ml of solution 1 are initially introduced, to which solution 2 is added dropwise (checking the pH, should be in the range from 7.5 to 8, possibly with NaOH solution (1M)) and then the mixture is refluxed for 6 hours After the reaction solution has cooled, the precipitate is filtered off with suction and dried to give a white precipitate The mixture is calcined at 600 ^° C. for 5 hours. Example 5 Preparation of the Red Phosphor Nao, ₅ Lao, ₃ Eu _{0) 2} Mo0 ₄ by Complexation with Citric Acid

1.024 g of molybdenum (IV) oxide are dissolved in 10 ml of H ₂ O ₂ (30%) with gentle heating. To the yellow solution, add 4.608 g of citric acid, together with 10 ml of dist. H ₂ O given.

Subsequently, 1.040 g of La (NO ₃ ) x 6 H ₂ O and 0.714 g of Eu (NO ₃ ) x 6 H ₂ O and 0.340 g of NaNO _{3 are} added and made up to 40 ml. The yellow solution is dried in a vacuum drying cabinet, initially forming a blue foam, from which finally results in a blue powder. Subsequently, the solid is annealed at 800 ^° C. for 5 hours.

Example 6: Preparation of the red phosphor Nao, sLao, 3Eu _o . ₂ (W0 ₄ ) o, s

2.120 g of lanthanum chloride hexahydrate and 1.467 g of europium chloride hexahydrate are dissolved in 100 ml of demineralized water [solution 1]. At the same time, a solution of 1.815 g of sodium molybdate dihydrate and 2.474 g of sodium tungstate dihydrate in 100 ml of deionized water is prepared [solution 2]. From solution 1, 100 ml are introduced, to this solution 2 is added dropwise (pH should be in the range of 7.5 - 8, possibly with NaOH solution (1 M) correct). Subsequently, the mixture is refluxed for 6 hours. After cooling the reaction solution, the precipitate is filtered off and dried, then calcined at 600 ⁰ C for 5 h.

Example 7: Preparation of the red phosphor La ₁₁₂ Eu _01S MoO ₄ by complexing with citric acid 1.024 g of molybdenum (IV) oxide are dissolved in 10 ml of H ₂ O ₂ (30%) with gentle heating. To the yellow solution, add 4.608 g of citric acid, together with 10 ml of dist. H ₂ O given. Subsequently, 1.040 g of La (NO ₃ ) x 6 H ₂ O and 0.714 g of Eu (NO ₃ ) x 6 H ₂ O and 0.340 g of NaNO _{3 are} added and made up to 40 ml. The yellow solution is dried in a vacuum drying cabinet, initially forming a blue foam, from which finally results in a blue powder. The solid is then calcined at 600 ^° C. for 5 hours.

Example 8: Preparation of the red phosphor Lai, ₂ Euo, ₈ W0 ₄ by complexing with citric acid

0.9711 g of tungsten (IV) oxide are added with gentle heating in 10 ml of H ₂ O ₂

(30%) solved. Simultaneously, a solution of 0.7797 g La (NOs) ₃ -6 H ₂ O, Eu (NO ₃₎ ₃ -6 H represented 0.5353 g ₂ O and 1, 8419 g citric acid in 40 ml H ₂ O and the blue tungstenate sol. given. The blue solution is dried in a vacuum drying cabinet, initially forming a blue foam, from which finally results in a blue powder. The solid is then calcined at 600 ^° C. for 5 hours

Example 9 Production of the Red Phosphor (Gdo. ₆ Euo.4) 2 (W0 ₄ ) i.5Pθ4

2.23 g of GdCl ₃ .6H ₂ O and 1.465 g of EuCl ₃ .6H ₂ O are dissolved in 100 ml of ethylene glycol (solution 1).

There are 1, 73 g of Na ₂ WO _{4 dissolved} in 70 ml of H ₂ O (solution 2). There are 0.74 g K ₃ PO _{4 dissolved} in 70 ml of ethylene glycol (solution 3). 100 ml of solution 1 are placed in an Erlenmeyer flask. To this, 70 ml of solution 3 are added first. The solution becomes cloudy but becomes clear again after brief stirring. Subsequently, a mixture of 70 ml of solution 2 and 5 ml of NaOH solution. (1M) added dropwise. The reaction mixture is transferred to a three-necked flask and heated for at least 6 h with stirring and reflux.

250 ml of acetone are added dropwise to the reaction solution. The precipitate is then removed by centrifuging and washed once more with acetone. The product is then annealed for 4 hours at 650 ⁰ C in the oven.

Example 10 Production of the Green-emitting Phosphor Ba ₂ SiO ₄ = Eu

390 g of barium carbonate, 3.5 g of europium (III) oxide, 63 g of silica gel (SiO ₂ ) and 5.4 g of ammonium chloride are mixed by grinding. The mixture is annealed over a period of 8 h in CO atmosphere at 1100 ^c C. After pulverization, a further 5.4 g of ammonium chloride are added and mixed well homogeneously. This mixture will now turn into CO

Atmosphere annealed at 1200 ⁰ C for 14 h. After milling, the powder is washed with water to remove excess halides and air dried.

Example 11: Preparation of the Green-emitting Phosphor Lu ₃ Al ₅ Oi ₂ = Ce

537.6 g of ammonium bicarbonate are dissolved in 3 liters of deionized water. 205.216 g of aluminum chloride hexahydrate, 228.293 g of lutetium chloride, water-containing (x H ₂ O) and 3.617 g of cerium chloride hexahydrate are dissolved in about 400 ml of deionized water and added rapidly to the bicarbonate solution. drips, while the pH value by addition of conc. Ammonia are kept at pH 8. Then it is stirred for another hour. After aging, the precipitate is filtered off and dried in a drying oven at about 12O ⁰ C.

The dried precipitate is crushed and then calcined for 4 hours at 1000 ° C in air. The product is then mortared again and calcined at 1700 ⁰ C in forming gas for 8 hours.

Example 12: Production of an LED and Installation in a Liquid Crystal Display

The phosphor from Example 10 (green phosphor) and the red phosphor from Example 6 are used in a quantitative ratio of 1: 2.17 in both components A and B of a silicone resin system OE 6336 from Dow

Corning mixed with the aid of a tumble mixer, so that the phosphor concentration in the two components A and B is 10 wt%. Then 2.2 wt% of silica gel powder from Merck for thixotroping are added to both mixtures and the resulting mixtures are homogenized again in a tumble mixer. In each case 5 ml of the component

A and 5 ml of component B are mixed homogeneously and filled into a cartridge, which is connected to the dispensing valve of a dispenser. In the dispenser, COB (chip on board) raw LEDs consisting of bonded InGaN chips each having a surface area of 1 mm ² and emitting at 450 nm wavelength are fixed. By means of the xyz positioning of the dispensing valve, domes are applied to each chip. The domes consist of the thixotropic mixture of the two silicone components and the two phosphors, as well as the silica gel powder. The thus treated COB LEDs are then exposed to a temperature of 15O ⁰ C, in which the silicone is solidified. The LEDs can now be put into operation and emit white light a color temperature of 6000 K.

Several of the LEDs manufactured above are then incorporated into a backlight system of a liquid crystal display.

Description of the drawings

In the following the invention will be explained in more detail by means of exemplary embodiments:

1 shows a schematic representation of the liquid-crystal display according to the invention (direct-lit version) (1 = LCD unit without background illumination, 2 = backlight unit, 3 = diffuser, 4 =

LED with phosphor layer according to the invention; 5 = homogeneous luminous flux of the backlight unit)

2 shows a schematic representation of the liquid crystal display (side-lit version) according to the invention (1 = LCD unit without backlighting; 2 = backlight unit; 3 = diffuser; 4 = LED with phosphor layer according to the invention; 5 = homogeneous luminous flux of the backlight unit )

Claims

claims

1. A liquid crystal display equipped with a backlight system with at least one white light source, which contains at least one semiconductor diode and at least one phosphor layer of a combination of at least two phosphors, wherein at least one phosphor emits red light and at least one phosphor emits green light.

2. A liquid crystal display according to claim 1, characterized in that the white light source luminescent IndiumAluminiumGalliumNitrid- semiconductor, in particular the formula InjGajAl _k N, wherein 0 <i, 0 <j, 0 <k, and i + j + k = 1 contains.

3. A liquid crystal display according to claim 1 and / or 2, characterized in that the white light source contains a blue emitting InGaN semiconductor.

4. Liquid crystal display according to one or more of claims 1 to 3, characterized in that the phosphor layer contains a red emitting phosphor as europium (lll) - or chromium (lll) -activated line emitter.

5. A liquid crystal display according to claim 4, characterized in that the phosphor layer as a red-emitting phosphor europium (lll) - o- the chrome (lll) -activated line emitter selected from the group AI ₂ O ₃ : Cr, Nao.5Gdo.3Euo .2WO4, Nao.5Yo.4Euo.-i MoO ₄ , Nao.5Lao.3Euo.2WO4, Nao.5La ₀ .3Euo.2MoO ₄ , Na ₀₁ SLa _{0 3} Eu _{0 2} (WO ₄ ) o. ₅ (MoO ₄₎ o.5, LaI Eu ₂ _{0 8} MoO _4, La _{I 2} _{0 8} Eu WO _4, (Gd _0. ₆ Eu _0. ₄₎ ₂ (WO ₄₎ ₄ ₁ .5PO contains.

6. Liquid crystal display according to one or more of claims 1 to 5, characterized in that the phosphor layer is a green emitting phosphor as Cer (Hl) - or Europium (II) -activated phosphor selected from the group of thiogallates, silicates, Oxonitridosilikate, aluminates, nitrides or grenade contains.

7. backlight system having at least one white light source, which contains at least one semiconductor diode and at least one phosphor layer of a combination of at least two phosphors which emit red and green light.

8. backlight system according to claim 7, characterized in that the white light source is a luminescent indium-aluminum gallium nitride semiconductor, in particular the formula InjGa _j Al _k N, where 0 <i, 0 <j, 0 <k, and i + j + k = 1 contains.

9. backlight system according to claim 7 and / or 8, characterized in that the white light source contains a blue-emitting In-GaN semiconductor.

10. backlight system according to one or more of claims 7 to 9, characterized in that the phosphor layer contains a red emitting phosphor as europium (lll) - or chromium (lll) -activated line emitter.

11. backlight system according to one or more of claims 7 to 10, characterized in that the phosphor layer is a red emitting phosphor as Europium- or chromium-activated line emitter selected from the group AI ₂ O ₃ : Cr, Nao.5Gdo.3Euo.2WO4, Na ₀ .5Yo.4Eu ₀ .iMoO ₄ , NaO ₁ SLa ₀₃ Eu ₀₂ WO ₄ , Na _{0 5} La _{0 3} Eu ₀₂ MoO ₄ , Na ₀ ^ La _{0 3} Eu _0-2 (WO ₄ ) o.5 (MoO ₄ ) o.5, LaL ₂ Eu _{0 8} MoO ₄ , La _{1 2} Eu _{0 8} WO ₄ , (Gd ₀ .6Euo.4) 2 (WO ₄ ) i contains 5PO4.

12. backlight system according to one or more of claims 7 to 11, characterized in that the phosphor layer is a green emitting phosphor as cerium (lll) - or europium (II) -activated phosphor selected from the group of thiogallates, silicates, oxonitridosilicates, aluminates, nitrides or grenade contains.

13. A white light source which contains a blue-emitting indium-aluminum-gallium nitride semiconductor, in particular of the formula InjGa _j Al _k N, where 0 <i, 0 <j, 0 <k, and i + j + k = 1, and a phosphor layer having a combination of at least two phosphors emitting red and green light.

14. White light source according to claim 13, characterized in that it contains a blue emitting InGaN semiconductor.

15. White light source according to claim 13 and / or 14, characterized in that the phosphor layer comprises a red-emitting phosphor as European

Contains (III) or chromium (III) activated line emitter.

16. White light source according to one or more of claims 13 to 15, characterized in that the phosphor layer is a green-emitting phosphor as cerium (lll) - or europium (II) -activated phosphor selected from the group of thiogallates, silicates, oxonitridosilicates , Aluminates, nitrides or garnets.

17. A method for producing a liquid crystal display equipped with a backlight system with a white light source, comprising the following steps: Producing at least one LED, which consists of a blue-emitting InGaAIN semiconductor, in particular the formula InjGa _j Al _k N, where 0 <i, 0 <j, 0 <k, and i + j + k = 1, as well as composed of a phosphor layer containing a combination of a red and green emitting phosphor.

• Installation of one or more LEDs in a housing to a backlight system, including diffusers and reflectors.

The backlight system is assembled with a corresponding liquid crystal unit containing a front panel with a color filter system for liquid crystal display.