SEMICONDUCTING LIGHT EMITTING MATERIAL

Abstract

Suggested is a semiconductor nano-sized light emitting material having a ligand.

Claims

1. A semiconductor nano-sized light emitting material comprising of a core, optionally one or more shell layers and a ligand coated onto the core or the outermost surface of the shell layers, wherein the ligand is at least one thio metal salt.

2. The material of claim 1, wherein said ligand is represented by formula (I) ##STR00011## in which M stands for a bivalent metal, preferably zinc, magnesium, copper or their mixtures; X stands for —O— or —S— or —NR.sup.2—; Y.sup.1 stands for —O— or —S—; R.sup.1, R.sup.2 stand independently from each other for an alkyl, alkenyl, alkenyl, aryl and/or aralkyl chain having 2 to 25 carbon atoms, optionally substituted by a functional group; or a group according to formula (II) and/or (III)
—(CHR.sup.5).sub.xO(CHR.sup.5).sub.y2—NR.sup.3R.sup.4   (II)
—(CH.sub.2CHR.sup.5O).sub.2R.sup.6   (III) R.sup.3, R.sup.4 stand independently from each other linear or branched alkyl chains having 1 to 6 carbon atoms; R.sup.5 stands for hydrogen or methyl; R.sup.6 stands for an alkyl chain having 1 to 4 carbon atoms, optionally substituted by a functional group; x, y2 stand independently from each other for integers of from 1 to 5; and z stands for an integer of from 1 to 30.

3. The material according to claim 1, wherein said ligand is represented by formula (I) and wherein R.sup.1, R.sup.2 stand independently from each other for an alkyl, alkenyl, alkenyl, aryl and/or aralkyl chain having 7 to 20 carbon atoms, optionally substituted by a functional group.

4. The material according to claim 1, wherein the ligand is a metal dialkyl thiocarbamate and/or a metal dialkyl dithiocarbonate and/or a metal alkyl trithiocarbamate.

5. The material according to claim 1, wherein said core is formed from one, two or more compounds according to formula (IV),
[A.sup.1B.sup.1]  (IV) in which [A.sup.1] stands for a metal selected from the group consisting of zinc, cadmium, indium or their mixtures; [B.sup.1] stands for a non-metal selected form the group consisting of sulphur, selenium, phosphor or their mixtures.

6. The material of claim 5, wherein [A.sup.1B.sup.1] stands for one, two or more compounds selected from the group consisting of CdS, CdSe, CdSeS, CdZnS, ZnS, ZnSe, ZnSeS, and InP.

7. The material according to claim 1, wherein said shell or said shells are formed from one, two or more compounds according to formula (V),
[A.sup.2B.sup.2]  (V) in which [A.sup.2] stands for a metal selected from the group consisting of zinc, cadmium or their mixtures; [B.sup.2] stands for a non-metal selected form the group consisting of sulphur, selenium, or their mixtures.

8. The material of claim 7, wherein [A.sup.2B.sup.2] stands for one, two or more compounds selected from the group consisting of CdS, CdSe, CdSeS, CdZnS, ZnS, ZnSe and ZnSeS, ZnSeSTe.

9. The material according to claim 1, wherein the material comprises a core [A.sup.1B.sup.1] and at least one shell [A.sup.2B.sup.2], said [A.sup.1B.sup.1]/[A.sup.2B.sup.2] being selected from the group consisting of CdSeS/CdZnS, CdSeS,CdS/ZnS, CdSeS/CdS,ZnS CdSe/ZnS, InP/ZnS, InP/ZnSe, InP/ZnSe,ZnS, InP(Zn)/ZnSe, InP(Zn)/ZnSe,ZnS, InP(Zn)/ZnSe,ZnS,ZnTe, ZnSe/CdS, ZnSe/ZnS or their mixtures.

10. A semiconductor nano-sized light emitting material comprising or consisting of a core, optionally one or more shell layers and a ligand coated onto the core or the outermost surface of the shell layers, obtainable or obtained by the following steps: (a) providing at least one salt of at least one metal [A.sup.1] and/or [A.sup.2] optionally dissolved in a suitable solvent; (b) adding at least one source of at least one non-metal [B.sup.1] and/or [B.sup.2] to obtain an intermediate compound [A.sup.1B.sup.1]/[A.sup.2B.sup.2]; (c) coating said intermediate compound [A.sup.1B.sup.1]/[A.sup.2.sub.B.sup.2] from step (b), optionally in the presence of a solvent, by bringing it into contact with a source of a thio metal salt, and optionally (d) subjecting said coated intermediate of step (c) to illumination with light with a peak light wavelength of about 300 to about 650 nm to increase quantum yield of the nano-sized material.

11. A process for manufacturing a semiconductor nano-sized light emitting material comprising or consisting of a core, optionally one or more shell layers and a ligand coated onto the core or the outermost surface of the shell layers, comprising or consisting of the following steps: (a) providing at least one salt of at least one metal [A.sup.1] and/or [A.sup.2] optionally dissolved in a suitable solvent; (b) adding at least one source of at least one non-metal [B.sup.1] and/or [B.sup.2] to obtain an intermediate compound [A.sup.1B.sup.1] or [A.sup.1B.sup.1]/[A.sup.2B.sup.2]; (c) coating said intermediate compound [A.sup.1B.sup.1]/[A.sup.2B.sup.2] from step (b), optionally in the presence of a solvent, by bringing it into contact with a source of a thio metal salt, and optionally (d) subjecting said coated intermediate of step (c) to illumination with light with a peak light wavelength of about 300 to about 650 nm to increase quantum yield of the nano-sized material.

12. A composition comprising at least one semiconductor nano-sized light emitting material according to claim 1, and at least one matrix material.

13. A formulation comprising at least one semiconductor nano-sized light emitting material according to claim 1, and at least one solvent.

14. An electronic device, optical device or a biomedical device comprising in said device semiconductor nano-sized light emitting material according to claim 1.

15. An optical medium comprising in said medium the semiconductor nano-sized light emitting material according to claim 1.

17. A compound of formula (I) ##STR00012## in which M stands for a bivalent metal, preferably zinc, magnesium, copper or their mixtures; X stands for —O— or —S— or —NR.sup.2—; Y.sup.1 stands for —O— or —S—; R.sup.1, R.sup.2 stand independently from each other for an alkyl, alkenyl, alkenyl, aryl and/or aralkyl chain having 7 to 25 carbon atoms, optionally substituted by a functional group; or a group according to formula (II) and/or (III)
—(CHR.sup.5).sub.xO(CHR.sup.5).sub.y2—NR.sup.3R.sup.4   (II)
—CH.sub.2CHR.sup.5O).sub.zR.sup.6   (III) R.sup.3, R.sup.4 stand independently from each other linear or branched alkyl chains having 1 to 6 carbon atoms; R.sup.5 stands for hydrogen or methyl; R.sup.6 stands for an alkyl chain having 1 to 4 carbon atoms, optionally substituted by a functional group; x, y2 stand independently from each other for integers of from 1 to 5; and z stands for an integer of from 1 to 30.

Description

WORKING EXAMPLES

[0185] Several semiconductors are prepared and subjected to surface treatment. Subsequently they are irradiated to enhance/improve quantum yields.

[0186] For illumination, a lighting setup built with Philips Fortimo 3000 Im 34W 4000K LED downlight module (phosphor disc removed). A 1.9 nm thick Perspex pane® is placed on its top. The distance between the LEDs and the Perspex pane® is 31.2 mm. The 20 ml sealed sample vials is placed on the Perspex pane® inside a plastic cylinder (diameter 68 mm, height 100 mm). A photo enhancement system with sealed sample vials inside the cylinder is used. The vials with the solution of QDs are placed on the Perspex and illuminated from below. Optionally, to prevent the solution from extensive heating and evaporation of the solvent, the vials are placed in the water bath. The peak wavelength of the illumination is 455 nm. The irradiance at 450 nm is measured by an Ophir Nova Il® and PD300-UV photodetector and measured to be 300 mW/cm.sup.2.

Example 1

Synthesis of InP/ZnSe

[0187] 112 mg of InI.sub.3, and 150 mg ZnCl.sub.2 are dissolved in 2.5 mL oleylamine. At 180° C. 0.22 mL of hexaethylphosphorous triamide (DEA).sub.3P) is added to the solution and is kept at this temperature for 20 min. After 20 min, 0.55 mL of anion shell precursor (2M TOP:Se) is added slowly in the solution. The solution is then heated stepwise, followed by successive injections of cation (2.4 mL of 0.4M Zn-acetate in oleylamine) and anion (0.38 mL of 2M TOP:Se) shell precursor at temperatures between 200° C. and 320° C.

Example 2

Synthesis of Zn-dioctadecyldithiocarbamate (Zn(C18)DTC)

[0188] ##STR00008##

[0189] Into 100 mL round bottom flask equipped with Claisen adapter, magnetic stirrer and equalizing pressure dropping funnel, dioctadecylamine (>99% from Sigma-Aldrich, 4.8 mmol) is placed. Then carbon disulfide (anhydrous, ≥99% from Sigma-Aldrich, 9.6 mmol, 2 Equivalents) is added to dissolve the amine completely. NaOH (4.9 mmol, 1.0 Equivalents) are dissolved at room temperature (20° C.) with deionized water. After addition of NaOH solution, the colour changed to yellow. The reaction is allowed to stir for two days under ambient atmosphere until all the CS.sub.2 evaporated and precipitate (dioctadecyl dithiocarbamate sodium salt) is formed. The work-up process includes vacuum filtration by Buchner.

[0190] Subsequently the dithiocarbamate thus obtained is reacted with Zinc chloride to form a zinc complex. Into 150 mL round bottom flask equipped with Claisen adapter, magnetic stirrer and equalizing pressure dropping funnel, dioctadecylamine sodium salt (1.5 mmol) dissolve at room temperature in ethanol: chloroform 1:1 is placed. In the next step ZnCl.sub.2 (0.9 mmol, 0.61 Equivalents) is dissolved at room temperature in an ethanol:chloroform 1:1 mixture, placed into the equalizing pressure dropping funnel and added dropwise for 15 minutes. Precipitate is formed after one day. Additional stirring of the mixture is allowed for 72 hours at 20° C., and then work-up using a vacuum filtration by Buchner is conducted. The white yellow solid dries over Buchner funnel for 2 hours under vacuum.

Example 3

Synthesis of Zn-oleyl xanthate

[0191] ##STR00009##

[0192] Into 50 mL Erlenmeyer, KOH and oleyl alcohol (85% grade, Sigma-Aldrich) are placed and reacted at 20° C. for 4 hours. After partially dissolving of KOH, the turbid solution is decanted (using the liquor) into 3-neck round bottom flask (3-rbf) equipped with magnetic stirrer and reflux condenser (only for protection) and equalizing pressure dropping funnel. Carbon disulfide dissolved in diethyl ether (12 mL) is placed into the equalizing pressure dropping funnel and added dropwise for 30 minutes. During the addition, pale yellow solid is formed. The reaction is allowed to stir 10 hours at 20° C. under dark conditions until most of the moisture is vanished. During stirring, most of the crude becomes solid. The work-up process included vacuum filtration by Buchner or drying by vacuum. Trituration is done with diethyl ether to obtain pure oleyl xanthate potassium salt.

[0193] Subsequently the xanthate thus obtained is reacted with Zinc chloride to form a zinc complex. Into 100 mL round bottom flask equipped Claisen adapter, magnetic stirrer and equalizing pressure dropping funnel, oleyl xanthate potassium salt (3.4 mmol) dissolve at room temperature (r.t) in THF is placed. In the next step ZnCl.sub.2 (2.1 mmol, 0.61 Equivalents) dissolved at room temperature in THF is placed into the equalizing pressure dropping funnel and added dropwise for 10 minutes. Precipitate of white solid is formed after 24 hours. Additional stirring of the mixture is allowed for 2 days at 20° C., and then the product is worked-up using a vacuum filtration by Buchner. The white solid is rinsed 3 times with deionized water and then dried over vacuum.

Example 4

Purification of Quantum Material from EXAMPLE 1

[0194] 1 mL of the sample from EXAMPLE 1 is purified from excess ligands using toluene and ethanol as solvent and anti-solvent respectively followed by centrifugation and drying. The cleaning is repeated twice. The amount of organic ligands is calculated using thermal gravimetric analysis (TGA) (model TGA2, Metier Toledo). TG analysis shows 14% wt. of organic content.

[0195] 30 mg of the quantum materials is dissolved in 1 mL toluene. Quantum yield (QY) is measured using Hamamatsu absolute quantum yield spectrometer (model: Quantaurus C11347). The solution is illuminated for 24 hours under blue led (300mW/cm.sup.2). The quantum yield of the illuminated sample is measured right after the illumination has stopped and 2 days after stopping the illumination.

Example 5

Surface Treatment with Zn-diethyl dithiocarbamate (Zn(C2)DTC)

[0196] 0.027 mmol Zn(C2)DTC

##STR00010##

[0197] (97%, 329703-25G from Sigma—Aldrich) are dissolved in 0.5 mL toluene. Sonication (10 minutes) is applied to accelerate dissolving of Zn(C2)DTC in toluene. The solution is combined with 1 mL of the purified QDs solution (see EXAMPLE 4). Sonication is applied over about 20 minutes until a clear solution is obtained.

Example 6

Illumination of QM Treated with Zn-diethyl dithiocarbamate (Zn(C2)DTC)

[0198] The solution from (EXAMPLE 5) is placed under illumination for 24 hours under blue led (300 mW/cm.sup.2). After 24 hours, the quantum yield of the sample is measured using Hamamatsu absolute quantum yield spectrometer (model: Quantaurus C11347). The quantum yield of the illuminated sample is measured right after the illumination has stopped and 2 days after stopping the illumination.

Example 7

Surface Treatment with Zn-dioctadecyl thiocarbamate (Zn(C18)DTC)

[0199] 0.027 mmol Zn(C18)DTC (from EXAMPLE 2) are dissolved in 0.5 mL toluene. Sonication (10 minutes) is applied to accelerate dissolving of Zn(C18)DTC in toluene. The solution is combined with 1 mL of the purified QDs solution (see EXAMPLE 4). Sonication is applied over about 20 minutes until a clear solution is obtained.

Example 8

[0200] Illumination of QM Treated with Zn(C18)DTC

[0201] A solution described in (EXAMPLE 7) is placed under illumination for 24 hours under blue led (300 mW/cm.sup.2). After 24 hours, the quantum yield of the sample is measured using Hamamatsu absolute quantum yield spectrometer (model: Quantaurus C11347). The quantum yield of the illuminated sample is measured right after the illumination has stopped and 2 days after stopping the illumination.

Example 9

Surface Treatment with Dioctadecyl dithiocarbamate (C18DTC)

[0202] 0.027 mmol C18DTC (prepared as described in EXAMPLE 2) are dissolved in 0.5 mL toluene. Sonication (10 minutes) is applied to accelerate dissolving of C18DTC in toluene. The solution is combined with 1 mL of the purified QDs solution (see EXAMPLE 4). Sonication is applied over about 20 minutes until a clear solution is obtained.

Example 10

Surface Treatment with Zn-oleyl xanthate (Zn(C18)xanthate)

[0203] 0.027 mmol Zn(C18)xanthate (prepared as described in EXAMPLE 3) are dissolved in 0.5 mL toluene. Sonication (10 minutes) is applied to accelerate dissolving of Zn(C18)xanthate in toluene. The solution is combined with 1 mL of the purified QDs solution (see EXAMPLE 4). Sonication is applied over about 20 minutes until a clear solution is obtained.

Example 11

Illumination of QM Treated with Zn(C18)xanthate

[0204] A solution described in (EXAMPLE 10) is placed under illumination for 24 hours under blue led (300 mW/cm.sup.2). After 24 hours the quantum yield of samples is measured using Hamamatsu absolute quantum yield spectrometer (model: Quantaurus C11347). The quantum yield of the illuminated sample is measured right after the illumination has stopped and 2 days after stopping the illumination.

[0205] The experimental results are presented in the following Tables 1 and 2 providing quantum yields and stability of Quantum yields of the samples.

TABLE-US-00001 TABLE 1 Quantum yield for Zn-dialkyl-DTC treated samples Samples QY (%) EXAMPLE 4 before illumination 21 EXAMPLE 4 after illumination 40 EXAMPLE 5 33 EXAMPLE 6 53 EXAMPLE 7 33 EXAMPLE 8 61 EXAMPLE 9 0.4 EXAMPLE 10 33 EXAMPLE 11 39

[0206] The EXAMPLES clearly indicate that the presence of a metal cation, here zinc, is crucial. EXAMPLE 5 for Zn(C18)DTC QY is 33% (before illumination), and only 0.4% for C18DTC (EXAMPLE 9). Moreover, Illumination can enhance QY significantly, and QY can significantly be increased when using Zn(C18)DTC.

TABLE-US-00002 TABLE 2 Stability of QY of the QM treated with different Zn-dialkylDTC (and xanthate), 48 hours after stopping illumination QY measure 2 days after Samples stopping illumination (%) EXAMPLE 4 21 EXAMPLE 6 21 EXAMPLE 8 59 EXAMPLE 11 41

[0207] The EXAMPLES clearly indicate that QY of InP/ZnSe (purified sample without external ligands) is not stable after stopping illumination and drops from 40% to 21%. InP/ZnSe with Zn(C2)DTC is also not stable. However, zinc dithio ligands with chain length of C18 (EXAMPLES 8 and 11) are stable and no drop in QY is observed.

Example 12

Synthesis and Purification of InP/ZnSe Quantum Dots

[0208] 112 mg of InI.sub.3, and 150 mg ZnCl.sub.2 are dissolved in 2.5 mL oleylamine. At 180° C. 0.22 mL of hexaethylphosphorous triamide (DEA).sub.3P) is added to the solution and is kept at this temperature for 20 min. After 20 min, 0.55 mL of anion shell precursor (2M TOP:Se) is added slowly in the solution. The solution is then heated stepwise, followed by successive injections of cation (2.4 mL of 0.4M Zn-acetate in oleylamine) and anion (0.38 mL of 2M TOP:Se) shell precursor at temperatures between 200° C. and 320° C., to obtain crude InP/ZnSe. 1 mL of the crude QDs is purified from excess ligands using toluene and ethanol as solvent and anti-solvent respectively followed by centrifugation and drying. The cleaning is repeated twice. The amount of organic ligands is calculated using thermal gravimetric analysis (TGA) (model TGA2, Metier Toledo). TG analysis shows 15% wt. of organic content.

Example 13

Stability Test by Dilution of QDs (from EXAMPLE 12)

[0209] 25 mg of QDs from EXAMPLE 12 are dissolved in 1 ml toluene (anhydrous grade). The solution is kept under inert atmosphere (Argon). This solution is further diluted to a final concentration of 0.3 mg/ml. The QY is measured right after the dilution and after 24 hours of storage under ambient conditions.

Example 14

Stability Test by Dilution of QDs (from EXAMPLE 12) After Surface Treatment with Zinc oleylxanthate

[0210] 25 mg of QDs (from EXAMPLE 12) are dissolved in 1 mL toluene (anhydrous grade). The solution is kept under inert atmosphere (Argon). ZnC18Xanthate (prepared as described in EXAMPLE 3) (10 mg) is added to the QDs solution and the mixture is stirred for 16 hours. This solution is further diluted to a final concentration of 0.3 mg/ml. The QY is measured right after the dilution and after 24 hours of storage under ambient conditions.

Example 15

Stability Test by Dilution of InP/ZnS QDs (Red Emitting QDs Manufactured as Described in WO02014/162206 A1 and /or U.S. Pat. No. 9,343,301 BB).

[0211] 25 mg of InP/ZnS (red emitting QDs manufactured as described in WO2014/162206 A1 and /or U.S. Pat. No. 9,343,301 BB) are dissolved in 1 ml toluene (anhydrous grade). The solution is kept under inert atmosphere (Argon). This solution is further diluted to a final concentration of 0.3 mg/ml. The QY is measured right after the dilution and after 24 hours of storage under ambient conditions.

Example 16

Stability Test by Dilution of InP/ZnS QDs (Red Emitting QDs Manufactured as Described in WO2014/162206 A1 and /or U.S. Pat. No. 9,343,301 BB) After Surface Treatment with Zn(C18)xanthate

[0212] 25 mg of InP/ZnS (red emitting QDs manufactured as described in WO2014/162206 A1 and /or US9,343,301 BB) are dissolved in 1 mL toluene (anhydrous grade). The solution is kept under inert atmosphere (Argon). Zn(C18)xanthate (10 mg) (prepared as described in EXAMPLE 3) is added to the QDs solution and the mixture is stirred for 16 hours. This solution is further diluted to a final concentration of 0.3 mg/ml. The QY is measured right after the dilution and after 24 hours of storage under ambient conditions.

Example 17

Stability Test by Dilution of InP/ZnS QDs (Red Emitting QDs Manufactured as Described in WO2014/162206 A1 and /or U.S. Pat. No. 9,343,301 BB) After Surface Treatment with Zinc Acetate

[0213] 25 mg of InP/ZnS (red emitting QDs manufactured as described in WO2014/162206 A1 and /or U.S. Pat. No. 9,343,301 BB) are dissolved in 1 ml toluene (anhydrous grade). The solution is kept under inert atmosphere (Argon). Zinc Acetate (10 mg) (Sigma Aldrich, 99.99% purity) is added to the QDs solution and the mixture is stirred for 16 hours. This solution is further diluted to a final concentration of 0.3 mg/ml. The QY is measured right after the dilution and after 24 hours of storage under ambient conditions.

TABLE-US-00003 TABLE 3 QY results from the stability tests by dilution QY measured right QY 24 hours after Sample after dilution [%] dilution [%] EXAMPLE 13 45 40 EXAMPLE 14 52 52 EXAMPLE 15 75 60 EXAMPLE 16 70 69 EXAMPLE 17 75 63

[0214] The results illustrated in Table 3 clearly show a stabilization of QY upon dilution when adding metal thiocarbonate as a ligand according to the invention. Therefore, the metal thiocarbonates not only lead to improvement of QY, they also lead to a stabilization of QY upon dilution and thus to an improvement of emission stability of QDs.