Down conversion

Abstract

The present invention relates inter alia to an array comprising i times j array elements, wherein the array elements may comprise at least one quantum dot and/or at least one photoluminescent compound. Further the present invention relates to devices comprising these arrays. The arrays and devices can be used to generate white light with high color purity.

Claims

1. An array, .sub.nm, of n times m array elements, A.sub.ij, wherein the array elements A.sub.ij are arrays of i times j elements a.sub.ij, wherein said array A.sub.ij comprises at least one composition comprising at least one quantum dot being localized in one or more of the array elements aij, and wherein n,m are, independent of each other, 1 or larger, wherein n+m is 3 or larger; i is a row index being 1 or larger; j is a column index being 1 or larger; with the proviso that if i=j=1 the composition of array element a.sub.11 comprises at least two quantum dots and at least one photoluminescent compound, wherein if said composition comprises more than one quantum dot, quantum dots showing a re-absorption rate of at least 5% are separated in different array elements.

2. The array of claim 1, wherein the compositions comprised by the array comprise at least one further photoluminescent compound.

3. The array of claim 1, wherein the shape of the array elements a.sub.ij is square, circular, oval, triangular, hexagonal, polygonal and irregular curved.

4. The array of claim 1, wherein less than 20% of the array elements a.sub.ij are transparent and do not comprise a composition comprising a quantum dot and/or a photoluminescent compound.

5. The array of claim 1, wherein said at least one quantum dot has an emission intensity maximum in the range between 380 and 700 nm.

6. The array of claim 1, wherein if said composition comprises more than one quantum dot, said quantum dots differ in their emission intensity maxima.

7. The array of claim 1, wherein said at least one quantum dot is selected from Group II-VI, Group III-V, Group IV-VI and Group IV semiconductors.

8. The array of claim 7, wherein said quantum dot is selected from the group consisting of ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, MgS, MgSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, PbTe, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, and a combination thereof.

9. The array of claim 1, wherein said at least one photoluminescent compound is selected from a fluorescent or phosphorescent material.

10. The array of claim 1, wherein said at least one photoluminescent compound has a broadband spectrum.

11. The array of claim 1, wherein said array further comprises at least one binder material and/or at least one organic dye.

12. A device comprising at least one array of claim 1.

13. The device of claim 12, wherein said device comprises a light source.

14. The device of claim 13, wherein said light source emits blue and/or ultraviolet light.

15. The device of claim 13, wherein said light source is a light emitting diode, organic light emitting diode, polymer light emitting diode, organic light emitting electrochemical cell, laser, or UV lamp.

16. A method for the generation of white light by down conversion through irradiating the array of claim 1 with blue or ultraviolet light.

17. A method for the preparation of the array of claim 1, said method comprising employing a printing technique.

18. The method of claim 17, wherein said printing technique is screen printing, ink jet printing, flexo printing, gravure printing, or offset printing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: Normalized photoluminescence spectrum of 1. YAG: Ce, 2. SEB-095, 3. PDY-132, 4. PDO-123, 5. black body at T=5200 K.

(2) FIG. 2: Emission spectrum of super white 1 (SW1)

(3) FIG. 3: Emission spectrum of super white 2 (SW2)

(4) FIG. 4: Emission spectrum of SW3-Ref, a superposition of SEB-095 and PDY-132.

(5) FIG. 5: Emission spectrum of super white 3 (SW3).

(6) FIG. 6: a) exemplary array with 10 columns and 10 rows comprising 9 different compositions (array elements) in a periodic arrangement; b) array with 6 rows and 1 column; c) array with 5 rows and 8 columns with hexagonal array elements.

(7) FIG. 7: Super array A.sub.41 (a) and A.sub.22 (b).

(8) FIG. 8: Device emitting white light comprising a blue organic light emitting diode (OLED) and a down-conversion layer (801) comprising a composition of the present invention, a substrate (802), such as glass or PET (polyethylene terephthalate), having an anode (803), a hole injection layer and/or a hole transport layer (804), an emissive layer (805), an electron transport layer or electron injection layer (806), a cathode (807) and an encapsulation (808).

(9) FIG. 9: Device emitting white light comprising a blue OLED and a down-conversion array (901), a substrate (902), such as glass or PET, having an anode (903), a hole injection layer and/or a hole transport layer (904), an emissive layer (905), an electron transport layer or electron injection layer (906), a cathode (907) and an encapsulation (908).

WORKING EXAMPLES

Example 1

(10) Materials

(11) The following materials can be used in the present invention as examples.

(12) Yellow emissive polymer PDY-132 (Merck KGaA) and orange emissive polymer PDO-123 (Merck KGaA) are used as organic photoluminescent materials. PDY-132 and PDO-123 are efficient polymeric fluorescent materials, having broad emission from 500 to 700 nm. Both are well soluble in common organic solvent, for example toluene, and show good film formation if coated from solution. In FIG. 1 the photoluminescence (PL) spectrum of thin films of PDY-132 (curve 3) and PDO-123 (curve 4) are shown in FIG. 1, in comparison with a white spectrum using a blue LED and phosphor YAG:Ce (curve 1) as down-converter. Here, the spectrum of PDY-132 shows the highest similarity with the spectrum of YAG:Ce. Curve 5 in FIG. 1 depicts the black body radiation at 5200 K. Further SEB-095 (Merck KGaA) is used as blue organic fluorescent material. The PL spectrum of SEB-095 is also shown in as curve 2 in FIG. 1.

(13) The following 8 quantum dots with core-shell structure are selected in combination with PDY-132 or PDO-123 in order to get a super white light. All quantum dots have PL spectrum of a (quasi-) Gaussian form if excited at 380 nm with a full width at half maximum (FWHM) of about 30 nm. The photoluminescent spectrums of the QDs are shown in FIG. 2 and the maximum wavelengths of QD1 to QD8 are as follows:

(14) TABLE-US-00001 Quantum Dot QD1 QD2 QD3 QD4 QD5 QD6 QD7 QD8 Max. 440 470 500 520 530 580 620 650 wavelength [nm]* *all fluorescence maximum range in +/5 nm

(15) QD1 to QD8 are core-shell type quantum-dots by Plasmachem GmbH, Berlin, Germany. QD1 to QD4 have a ZnCdSe spheric core capped with epitaxial ZnS shell. QD5 to QD8 have a CdSe spheric core capped with epitaxial ZnS shell. All QDs have a surface hydrophobic layer comprising mostly trioctylphosphine oxide. The different emission spectrums are realized by tuning the size of the core, for example QD5 has a core of 2.5 nm in diameter, whereas QD6 of 3.6 nm.

Example 2

(16) Super White1 (SW1)

(17) SW1 is prepared using a mixture of PDY-132 and QDs as down converter for a blue LED or UV light source.

(18) By using a thick enough layer comprising the mixture of the following composition, all blue light from the blue LED light source is absorbed. The mixture of following composition gives a broad emission spectrum as shown in FIG. 2.

(19) TABLE-US-00002 TABLE 1 Composition of the mixture for SW1. Concentration (conc.) is given in wt % PDY- QD1 QD2 QD3 QD4 QD5 QD6 QD7 QD8 132 Conc. 15.7 16.4 16.3 4.5 7.2 3.8 7.7 11.3 17.1

(20) The color rendering index (CRI), CIE coordinates and correlated color temperature of SW1 is calculated by employing the software CIE 13.3 Colour Rendering Index (1994) by International Commission on Illumination, Copyright @ 1994 Peter Sylvester, University of Veszprem. The results are summarized in Table, wherein Tc stands for correlated colour temperature, R1-R14 for the special colour rendering indices using 14 CIE test colour samples and the Ra for general colour rendering index calculated from the first eight special colour rendering indices. For more details please refer to CIE (1995), Method of Measuring and Specifying Colour Rendering Properties of Light Sources, Publication 13.3, Vienna: Commission Internationale de l'Eclairage, ISBN 978-3900734572, http://www.cie.co.at/publiabst/13-3-95.html (A verbatim re-publication of the 1974, second edition. As can be seen in Table 2, SW1 is a high quality white, having a general CRI as high as 96.

(21) TABLE-US-00003 TABLE 2 CRI, CIE coordinates and color temperature of different whites SW1 SW2 SW3 SW3-Ref CIEx 0.34 0.34 0.36 0.34 CIEy 0.36 0.36 0.40 0.38 Tc [K] 5108 5225 4638 5154 R1 95.8 98.4 91.9 70.1 R2 98.2 99.5 95.6 88.7 R3 98.9 99.2 90.9 91.2 R4 95.8 98.0 83.4 61.8 R5 96.3 98.7 90.6 70.2 R6 98.4 98.4 98.1 83.1 R7 96.8 97.5 87.2 79.9 R8 92.6 96.3 83.0 53.5 R9 80.5 91.3 66.3 23.9 R10 96.7 99.1 92.8 72.6 R11 97.2 99.3 86.8 55.0 R12 93.9 95.9 78.5 55.8 R13 96.4 99.0 92.9 75.2 R14 99.4 99.4 94.5 94.3 Ra 96.6 98.3 90.1 74.8

(22) The solution of the mixture in toluene is used for coating a thin layer.

Example 3

(23) Super White 2 (SW2)

(24) SW2 is prepared using a mixture of PDO-123 and QDs as down convert for a blue LED or UV light source.

(25) By using a thick enough layer comprising the mixture of the following composition, all blue light from the blue LED is absorbed. The mixture of following composition gives a broad emission spectrum as shown in FIG. 3.

(26) TABLE-US-00004 TABLE 3 Composition of the mixture for SW2. Concentration (conc.) is given in wt % QD1 QD2 QD3 QD4 QD6 QD7 QD8 PDO-123 Conc. 14.4 14.7 14.4 5.8 8.0 12.5 13.7 16.5

(27) The CRI, CIE coordinates and Tc of SW2 are calculated by software CIE 13.3 Colour Rendering Index (1994) and summarized in Table. Again, using PDO-123 in combination with quantum dots, an excellent white with a Ra as high as 98 can be achieved.

(28) The solution of the mixture in toluene is used for coating a thin layer.

Example 4

(29) Super White 3 (SW3)

(30) SW3 is prepared using a mixture of PDY-132, SEB-095 and QDs as down converter for a blue LED or UV light source.

(31) In this example, it will be shown that two organic fluorescent materials SEB-095 and PDY-132, in combination with quantum dots can be used to build a down converter with high quality white emission. An example (SW3) is given by using the mixture of the composition given in Table 4.

(32) TABLE-US-00005 TABLE 4 Composition of the mixture for SW2. Concentration (conc.) is given in wt % QD3 QD4 QD6 QD7 QD8 SEB-095 PDY-132 Conc. 7.81 11.84 4.79 11.34 15.87 25.19 23.16

(33) Additionally, a two color white (SW3-Ref) consisting of only SEB-095 and PDY-132 is compared to SW3. The ratio of SEB-095 and PDY-132 are the same in SW3 and SW3-Ref. The spectrum of SW3 and SW3-Ref are shown in FIG. 5 and FIG. 4, respectively. The results are also shown in Table 2.

(34) The solution of the mixture in toluene is used for coating a thin layer.

Example 5

(35) Super White 4 (SW4)

(36) SW4 is prepared using a mixture of PDY-132 and QDs as down converter for OLED.

(37) Using the mixture of Example 4 without SEB-095, but keeping the same ratio of others, a down-converter using the following OLED as blue light source can be achieved, which gives a white which is comparable to the white obtained with SW3.

(38) The OLED has a device structure of glass/ITO(150 nm)/PEDOT(20 nm)/HTM-014(30 nm)/NPB(20 nm)/SEB1(95%):SEB-095(5%)(30 nm)/Alq.sub.3(20 nm)/LiF(1 nm/A1(100 nm), wherein PEDOT (Baytron P AI 4083) is a buffer layer, HTM-014 a hole injection or transport material by Merck KGaA, NPB is N,N-Di(naphthalen-1-yl)-N,N-diphenyl-benzidine, and SEB1 is a host material having a structure as follows:

(39) ##STR00013##

(40) The PEDOT is coated by spin-coating and other layers are prepared by vacuum thermal evaporation, and finally encapsulated. More details on the preparation of OLEDs are disclosed in WO 2008/006449 A1.

(41) The electroluminescence spectrum of the OLED is comparable to the PL spectrum of SEB-095. The mentioned mixture without SEB-095 is coated on the top of the glass substrate of the OLED. The layer is thin enough to let the emission of the OLED partially though. By adjusting the thickness of the converter layer, a white spectrum comparable to the one of SW3 can be obtained.

(42) Such kind of converter can also be integrated in the OLED device, the so-called internal conversion, as disclosed in DE 102010006280.4.

Example 6

(43) Arrays with Different Domains (Array Elements)

(44) An stand alone conversion layer can be prepared by depositing the quantum dots and photoluminescent materials in different domains (array elements) of an array on a transparent substrate.

(45) The first example is shown in FIG. 6, wherein different pixels are defined on the substrate, and filled by the different components (9 components as shown in Example 2. By adjusting the pixel numbers for the different components, super white as SW1 to SW3 can be obtained. To let the light from a blue light source at least partially through, blank pixel can be used together with other pixels comprising either quantum dots or photoluminescent organic compounds or both. Blank pixel means here either an empty pixel or a pixel filled with binder, which is transparent to light of the light source and which emits no light.

(46) The second example is illustrated in FIG. 7, wherein different stripes (array elements or domains) are defined on the substrate, and filled by the different components (9 components as shown in Example 2. By adjusting the number of stripes or the width of the stripes for the different components, the white as SW1-3 can be obtained. To let the light from blue source partially through, blank stripes can be used together with other stripes. Blank stripes means here either an empty stripe or a stripe filled with binder, which is transparent to source light and emits no light.