Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
  • C09K11/06—Luminescent, e.g. electroluminescent, chemiluminescent materials containing organic luminescent materials
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
  • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
  • C09K11/66—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing germanium, tin or lead
  • C09K11/664—Halogenides
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
  • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
  • H10H20/01—Manufacture or treatment
  • H10H20/011—Manufacture or treatment of bodies, e.g. forming semiconductor layers
  • H10H20/013—Manufacture or treatment of bodies, e.g. forming semiconductor layers having light-emitting regions comprising only Group III-V materials
  • H10H20/0137—Manufacture or treatment of bodies, e.g. forming semiconductor layers having light-emitting regions comprising only Group III-V materials the light-emitting regions comprising nitride materials
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
  • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
  • H10H20/80—Constructional details
  • H10H20/85—Packages
  • H10H20/851—Wavelength conversion means
  • H10H20/8511—Wavelength conversion means characterised by their material, e.g. binder
  • H10H20/8512—Wavelength conversion materials
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
  • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
  • H10H20/80—Constructional details
  • H10H20/85—Packages
  • H10H20/851—Wavelength conversion means
  • H10H20/8511—Wavelength conversion means characterised by their material, e.g. binder
  • H10H20/8512—Wavelength conversion materials
  • H10H20/8513—Wavelength conversion materials having two or more wavelength conversion materials
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K2211/00—Chemical nature of organic luminescent or tenebrescent compounds
  • C09K2211/18—Metal complexes
  • C09K2211/188—Metal complexes of other metals not provided for in one of the previous groups

Definitions

• the present invention relates to a light emitting device comprising a light source and a luminescent material. Also described is a luminescent material comprising two or more types of nanoparticles and a process for producing luminescent materials and light emitting devices.
• a standard white light LED is typically composed of a blue GaN LED (440-470 nm emission) with a coating of either a yellow-green phosphor or a combination of red and green phosphors (multi-phosphor approach).
• the role of the phosphor is to absorb a certain fraction of the blue light, down-convert and reemit this light across the visible spectrum.
• Most commercially available single-phosphor pc-LEDs are based on Ce 3+ doped Yttrium Aluminum Garnet (YAG:Ce: Y3-xGd x Al5- y GayOi2:Ce) as the yellow-emitting phosphor material.
• Quantum dots synthesized from II- VI semiconductors can be employed in place of phosphors, since they can be tuned to radiate any color simply by changing the chemical composition and physical size of the dot, which is typically 2 - 10 nm. Semiconductor quantum dots have recently found applications in displays.
• Nontemplate synthesis of CH 3 NH 3 PbBr 3 perovskite nanoparticles describes the synthesis of perovskite nanocrystals in solution.
• NCs spectrally tuneable nano-crystals
• crystalline compounds for instance organic-inorganic metal halide perovskites.
• Both the tuneable chemistry of this family of materials and the quantum confinement of the NCs can be exploited to synthesise NCs with an emission wavelength over the entire range of the visible spectrum from 410 to 775 nm, with high quantum efficiency.
• the inventors have surprisingly found that nano-crystals of two or more different perovskites may be included in an insulating and transparent polymer matrix and subsequently used for fabricating perovskite NC/polymer composite films.
• the inventors have discovered that NCs with a range of emission wavelengths can be blended together in a common polymer host to create a film with white light emission with a tunable hue without rapid degradation of the white light emission due to ion exchange between different perovskites.
• the inventors have also demonstrated that multiple layers containing different NCs can be stacked on top of each other to realise true white light emission which is stable over time.
• the invention provides a light emitting device comprising a light source and a luminescent material, which luminescent material comprises:
• first plurality of nanoparticles comprising a first crystalline compound
• second plurality of nanoparticles comprising a second crystalline compound
• first crystalline compound and the second crystalline compound are different compounds of formula
• [A] is at least one cation
• [M] is at least one metal or metalloid cation
• [X] is at least one anion; a is an integer from 1 to 6;
• b is an integer from 1 to 6;
• c is an integer from 1 to 18.
• the invention also provides the use of a luminescent material as a phosphor in a light emitting device, which luminescent material comprises:
• first crystalline compound and the second crystalline compound are different compounds of formula
• [A] is at least one cation
• [M] is at least one metal or metalloid cation
• [X] is at least one anion
• a is an integer from 1 to 6;
• b is an integer from 1 to 6;
• c is an integer from 1 to 18.
• a luminescent material comprising one or more matrix materials and disposed in said matrix materials:
• [A] is at least one cation
• [M] is at least one metal or metalloid cation
• [X] is at least one anion
• a is an integer from 1 to 6;
• b is an integer from 1 to 6; and c is an integer from 1 to 18.
• the invention further provides a process for producing a light emitting device comprising a phosphor, which process comprises disposing a luminescent material as defined herein on a light source as defined herein.
• the invention also provides a process for producing a luminescent material, which process comprises combining a first plurality of nanoparticles comprising a first crystalline compound, a second plurality of nanoparticles comprising a second crystalline compound and one or more matrix materials, wherein said first and second crystalline compounds are different compounds of formula [A] a [M]b[X] c , wherein: [A] is at least one cation; [M] is at least one metal or metalloid cation; [X] is at least one anion; a is an integer from 1 to 6; b is an integer from 1 to 6; and c is an integer from 1 to 18.
• Figure 1 shows transmission electron micrographs of (MA/OA)PbBr3 perovskite NCs with varying OA + /MA + molar ratios.
• Figure 2 shows x-ray powder diffraction patterns for, from top to bottom, OABr, PbBr 2 , (OA) 2 PbBr 4 , (0.1MA/0.9OA)PbBr 3 , (0.4MA/0.6OA)PbBr 3 and MAPbBr 3 .
• Figure 3 shows photoluminescent emission intensity (dotted line) and UV-Vis absorbance (solid line) for perovskite NCs comprising varying ratios of octylammonium (OA+) and methylammonium (MA+) cations (i.e. MA + vs OA + ).
• Figure 4 shows the PLQE measurements when excited at 405 nm of perovskite NCs with varying OA+/MA+ molar ratios.
• Figure 5 shows time-resolved photoluminescence (PL) decays of perovskite NCs comprising varying ratios of octylammonium (OA+) and methylammonium (MA+) cations (i.e. MA + vs OA + .)
• Figure 6 shows PL intensity and absorbance of NCs synthesized with 90% OA which were separated by the centrifuging at 7000 rpm for varying durations.
• Figure 7 shows X-diffraction pattern of perovskite without (i.e. MAPbCb) and with the octylammonium cation (i.e. (0.6MA/0.4OA)PbCl 3 ).
• Figure 8 shows powder X-ray diffraction pattern of mixed halide NCs with varying amounts of different halides. The reflections at (101), (040) and (141) are marked by a dotted line.
• Figure 10 shows band gap vs stoichiometric ratio of halide ions in a variety of mixed halide perovskite NCs.
• Figure 13 shows the broad spectrum PL emission of a luminescent material comprising a range of different mixed halide perovskite NCs all embedded within a single polymer matrix.
• the dotted line is a semi- empirical spectrum calculated by adding together emission spectrum shown in Figure 10 with different weighting to each individual emission spectrum in order to closely match the air mass 1.5 natural daylight spectrum.
• Figure 14 shows the emissive wavelengths of three different perovskite NC comprising films.
• Figure 15 shows a white light spectrum produced by a blue LED together with a stack of the three perovskite NC films used in Figure 14.
• Figure 16 shows chromaticity colour coordinates (CIE) plotted from the corresponding perovskite NCs emissions.
• Figure 17 top, middle and bottom show three wide spectrum PL emission spectra of a perovskite NC blend in a polymer matrix (i.e. NC/polymer film).
• Figure 18 shows PL emission indicating halide ion exchange between perovskite nano- crystals suspended in toluene.
• Figure 19 shows the continued ion exchange between the nanocrystals after several minutes in solution and after several months in solution.
• Figure 20 shows the PL intensity ((a) and (b)) and absorbance ((c) and (d)) for a variety of mixed halide MAPbX 3 perovskites.
• Figure 21 shows the PL intensity for a variety of mixed halide MAPbX 3 perovskites.
• Figure 22 shows the PL intensity for MA(OA)PbI 3 perovskites with varying OA/MA ratios.
• Figure 23 shows the PL intensity for MA(OA)PbCl 3 perovskites with varying OA/MA ratios.
• perovskite refers to a material with a crystal structure related to that of CaTi0 3 or a material comprising a layer of material, which layer has a structure related to that of CaTi0 3 .
• the structure of CaTi0 3 can be represented by the formula ABX 3 , wherein A and B are cations of different sizes and X is an anion. In the unit cell, the A cations are at (0,0,0), the B cations are at (1/2, 1/2, 1/2) and the X anions are at (1/2, 1/2, 0). The A cation is usually larger than the B cation.
• the different ion sizes may cause the structure of the perovskite material to distort away from the structure adopted by CaTi0 3 to a lower-symmetry distorted structure.
• the symmetry will also be lower if the material comprises a layer that has a structure related to that of CaTi0 3 .
• Materials comprising a layer of perovskite material are well known.
• the structure of materials adopting the K 2 NiF4-type structure comprises a layer of perovskite material.
• a perovskite material can be represented by the formula [A][B][X] 3 , wherein [A] is at least one cation, [B] is at least one cation and [X] is at least one anion.
• the different A cations may distributed over the A sites in an ordered or disordered way.
• the perovskite comprises more than one B cation
• the different B cations may distributed over the B sites in an ordered or disordered way.
• the perovskite comprise more than one X anion
• the different X anions may distributed over the X sites in an ordered or disordered way.
• the symmetry of a perovskite comprising more than one A cation, more than one B cation or more than one X cation will be lower than that of CaTiOs.
• metal halide perovskite refers to a perovskite, the formula of which contains at least one metal cation and at least one halide anion.
• organic- inorganic metal halide perovskite refers to a metal halide perovskite, the formula of which contains at least one organic cation.
• hexahalometallate refers to a compound which comprises an anion of the formula [ ⁇ ] 11" wherein M is a metal atom, each X is independently a halide anion and n is an integer from 1 to 4.
• chalcogenide refers to an anion of the elements of group 16, for instance O 2" , S 2" , Se 2" , or Te 2" . Typically, the chalcogenides are taken to be S 2" , Se 2" , and Te 2" .
• the term "monocation”, as used herein, refers to any cation with a single positive charge, i.e. a cation of formula A + where A is any moiety, for instance a metal atom or an organic moiety.
• the term “dication”, as used herein, refers to any cation with a double positive charge, i.e. a cation of formula A 2+ where A is any moiety, for instance a metal atom or an organic moiety.
• the term “tetracation”, as used herein, refers to any cation with a quadruple positive charge, i.e. a cation of formula A 4+ where A is any moiety, for instance a metal atom.
• alkyl refers to a linear or branched chain saturated hydrocarbon radical.
• An alkyl group may be a C 1-20 alkyl group, a C 1-14 alkyl group, a Ci-io alkyl group, a Ci-6 alkyl group or a Ci-4 alkyl group.
• a Ci-io alkyl group are methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl.
• Examples of Ci-6 alkyl groups are methyl, ethyl, propyl, butyl, pentyl or hexyl.
• Ci-4 alkyl groups are methyl, ethyl, i-propyl, n-propyl, t-butyl, s-butyl or n-butyl. If the term "alkyl” is used without a prefix specifying the number of carbons anywhere herein, it has from 1 to 6 carbons (and this also applies to any other organic group referred to herein). An alkyl group is typically
• aryl refers to a monocyclic, bicyclic or polycyclic aromatic ring which contains from 6 to 14 carbon atoms, typically from 6 to 10 carbon atoms, in the ring portion. Examples include phenyl, naphthyl, indenyl, indanyl, anthrecenyl and pyrenyl groups.
• substituted refers to an organic group which bears one or more substituents selected from Ci-io alkyl, aryl (as defined herein), cyano, amino, nitro, Ci-io alkylamino, di(Ci-io)alkylamino, arylamino, diarylamino, aryl(Ci-io)alkylamino, amido, acylamido, hydroxy, oxo, halo, carboxy, ester, acyl, acyloxy, Ci-io alkoxy, aryloxy, halo(Ci-io)alkyl, sulfonic acid, thiol, Ci-io alkylthio, arylthio, sulfonyl, phosphoric acid, phosphate ester, phosphonic acid and phosphonate ester.
• substituents selected from Ci-io alkyl, aryl (as defined herein), cyano, amino, nitro, Ci
• substituted alkyl groups include haloalkyl, perhaloalkyl, hydroxyalkyl, aminoalkyl, alkoxyalkyl and alkaryl groups.
• a group When a group is substituted, it may bear 1, 2 or 3 substituents.
• a substituted group may have 1 or 2 substituents.
• the invention provides a light emitting device comprising a light source and a luminescent material, which luminescent material comprises: one or more matrix materials, and, disposed in said one or more matrix materials, a first plurality of nanoparticles comprising a first crystalline compound, and a second plurality of nanoparticles comprising a second crystalline compound, wherein the first crystalline compound and the second crystalline compound are different compounds of formula [A] a [M]b[X] c , wherein: [A] is at least one cation; [M] is at least one metal or metalloid cation; [X] is at least one anion; a is an integer from 1 to 6; b is an integer from 1 to 6; and c is an integer from 1 to 18.
• [X] is typically at least one halide anion or chalcogenide ion selected from S 2" , Se 2" , and Te 2" .
• [X] is typically at least one halide anion.
• a light emitting device is an electronic device which emits light. Examples of a light emitting device include a light emitting diode (LED), an organic light emitting diode
• OLED organic light emitting diode
• incandescent light bulb a halogen light bulb
• a noble gas light for instance a neon, argon or krypton light
• cathode ray tube a carbon arc lamp and a laser.
• the light emitting device is typically a light emitting diode.
• the light source may have a peak emission wavelength of from 300 nm to 800 nm.
• the luminescent materials of the invention are useful in producing white light from bluer light.
• the light source often has a peak emission wavelength of from 350 nm to 600 nm or from 400 nm to 500 nm.
• the light source may have a peak emission wavelength of from 450 nm to 500 nm. Peak emission wavelengths of light sources are readily available to the skilled person.
• the light source is the material or article which emits the light which emanates from the light emitting device. Typically, the light source is a light emitting diode.
• the light emitting device maybe a light emitting diode comprising said light emitting diode as a light source and the luminescent material.
• the light source may for instance be an inorganic LED or an organic LED.
• the LED may comprise, as a semiconductor, gallium(III) nitride (GaN), gallium(III) phosphide (GaP), aluminium gallium indium phosphide (AlGalnP), aluminium gallium phosphide (AlGaP), indium gallium nitride (InGaN) or silicon (Si).
• a commonly used blue LED is a gallium nitride (GaN).
• the light source is a light emitting diode comprising gallium nitride.
• a luminescent material is a material which emits light following the absorption of photons, i.e. a phosphorescent or fluorescent material.
• the luminescent material used in the device of the invention may be fluorescent, phosphorescent or both.
• the luminescent material may be in the form of a layer or a coating.
• the luminescent material acts as a phosphor by absorbing light emitted from the light source and re-emitting the light at a difference wavelength.
• the luminescent material is typically positioned between the light source and an outer surface of the light emitting device. For instance, if the light emitting device is a light emitting diode, the luminescent material is typically present as a coating on the transparent housing of the light emitting diode.
• the luminescent material may be present as a layer having a thickness of from 100 nm to 4 mm, for instance from 1 ⁇ to 1000 ⁇ or from 50 ⁇ to 500 ⁇ . In some cases the layer may have a thickness of from 1 to 4 mm, for instance if a free-standing layer is to be constructed. If the luminescent material comprises two or more layers each respectively comprising different nanoparticles, the thickness of each layer may be from 100 nm to 4 mm, for instance from 1 ⁇ to 1000 ⁇ or from 50 ⁇ to 500 ⁇ .
• the first and second crystalline compounds in the luminescent material may be any suitable luminescent crystalline compounds.
• a crystalline compound is a compound having an extended 3D crystal structure.
• a crystalline compound is typically in the form of crystals or crystallites (i.e. a plurality of crystals having particle sizes of less than or equal to 1 ⁇ ).
• Nanoparticles as defined herein, are typically particles having a particle size of from 1 to 1000 nm, for instance from 1 to 500 nm, or from 5 to 100 nm. Particle size is the diameter of a spherical particle having the same volume as the particle in question.
• the first and/or second crystalline compound is typically a compound of formula [A]a[M]b[X]c, wherein: [A] is at least one monocation or dication; [M] is at least one metal or metalloid cation; [X] is at least one halide anion; a is an integer from 1 to 3, b is an integer from 1 to 3, and c is an integer from 1 to 8. a is often 1 or 2. b is often 1 or 2. c is often from 3 to 6.
• the crystalline material may comprise a compound of formula A a (M 1 ,M 2 )bX c .
• the crystalline material may comprise a compound of formula A a Mb(X 1 ,X 2 ) c .
• [X] may represent one, two or more X ions. If [A], [M] or [X] is more than one ion, those ions may be present in any proportion.
• a a (M 1 ,M 2 )bX c includes all compounds of formula wherein y is between 0 and 1, for instance from 0.05 to 0.95. Such materials may be referred to as mixed ion materials.
• the first crystalline compound may for instance have the formula
• [A] is one or more cations such as those described herein, for instance one or more organic monocations;
• [M] is one or more first cations which are metal or metalloid cations selected from
• [X] is one or more second anions selected from CI “ , Br “ , ⁇ , S 2" , Se 2" , and Te 2" ;
• a is an integer from 1 to 3;
• b is an integer from 1 to 3;
• c is an integer from 1 to 8.
• the first and/or second crystalline compound is a perovskite compound which comprises at least one monocation, at least one metal or metalloid dication and at least one halide anion.
• the first and/or second crystalline compound is often a metal halide perovskite, and preferably an organic-inorganic metal halide perovskites.
• the luminescent material may comprise a first plurality of nanoparticles comprising a (first) metal halide perovskite and a second plurality of nanoparticles comprising a (second) metal halide perovskite.
• the first crystalline compound is a perovskite compound of formula (I):
• [A][M][X] 3 (I) wherein: [A] is at least one monocation; [M] is at least one metal or metalloid dication; and [X] is at least one halide anion.
• the second crystalline compound is also preferably a different perovskite compound of formula (I):
• the first and/or second crystalline compound is often a perovskite compound of formula (II): [A]M[X] 3 (II) wherein: [A] is two or more monocations; M is a single metal or metalloid dication; and [X] is at least one halide anion.
• the first and/or second crystalline compound is a layered perovskite compound of formula (Ha): [A] 2 [M][X] 4 (Ha) wherein: [A] is at least one monocation; [M] is at least one metal or metalloid dication; and [X] is at least one halide anion.
• the first and/or second crystalline compound may be a layered perovskite compound of formula (lib):
• the first and second crystalline compounds may be different layered perovskite compounds of formula (lib).
• each monocation may independently selected from cations of formula
• each monocation is independently selected from cations of formula (R 1 H 3 ) + , wherein R 1 is unsubstituted Ci-io alkyl. More preferably, each monocation is independently selected from cations of formula (R 1 H 3 ) + , wherein R 1 is unsubstituted methyl or ethyl.
• each monocation is often independently selected from cations of formula (R 1 H 3 ) + , wherein R 1 is unsubstituted C4- 2 o alkyl, for instance unsubstituted Cio-is alkyl.
• the first and/or second crystalline compound may for instance be a mixed cation perovskite compound of formula (II):
• R 1 may be selected from methyl, ethyl, hexyl, heptyl octyl.
• the first and/or second crystalline compound may alternatively be an inorganic perovskite compound of formula (II):
• [A] is one or more inorganic cations (e.g. Cs + or Rb + ); M is a single metal or metalloid dication; and [X] is at least one halide anion.
• each metal or metalloid dication is independently selected from Ca , Sr , Cd , Cu 2+ , Ni 2+ , Mn 2+ , Fe 2+ , Co 2+ , Pd 2+ , Ge 2+ , Sn 2+ , Pb 2+ , Yb 2+ and Eu 2+ .
• each metal or metalloid dication is independently selected Ge 2+ , Sn 2+ , Pb 2+ and Cu 2+ . More preferably, the metal or metalloid cation is Pb 2+ .
• each halide anion is independently selected from F “ , CI “ , Br “ and ⁇ .
• each halide anion is independently selected from CI “ , Br “ and ⁇ , for instance CI " or Br " .
• the first and/or second crystalline compound is selected from perovskite compounds of formula CH3 H3MX3, CH 3 H 3 MX X X' 3-X , (CH 3 H 3 )i- y (C 8 Hi 7 H 3 ) y MX 3 and (CH 3 H 3 )i- y (C 8 Hi 7 H 3 ) y MX x X' 3-x , wherein
• M is Cu 2+ , Pb 2+ , Ge 2+ or Sn 2+ ,
• X is a halide anion which is F “ , CI “ , Br “ or ⁇ ,
• X' is different from X and is a halide anion which is F “ , CI “ , Br “ or ⁇ ,
• x is from 0 to 3
• y is from 0 to 1. y may for instance be from 0.2 to 0.8. x is typically 0, 3 or from 0.5 to 2.5.
• the first and/or second crystalline compound may be a perovskite compound of formula (CH 3 H 3 )i -y (C 8 Hi 7 H 3 ) y MX 3 or (CH 3 H 3 )i- y (C 8 Hi 7 H 3 ) y MX x X' 3-x , wherein
• M is Cu 2+ , Pb 2+ , Ge 2+ or Sn 2+ ,
• X is a halide anion which is F “ , CI “ , Br “ or ⁇ ,
• X' is different from X and is a halide anion which is F “ , CI “ , Br “ or ⁇ ,
• x is from 0 to 3
• y is from 0.5 to 0.7, preferably from 0.55 to 0.65.
• each halide anion is independently Br “ , ⁇ or CI " .
• the first and/or second crystalline compound may be a perovskite compound selected from CH 3 H 3 PbI 3 , CH 3 H 3 PbBr 3 , CH 3 H 3 PbCl 3 , CH 3 H 3 PbF 3 , CH 3 H 3 PbBr x I 3-x , CH 3 H 3 PbBr x Cl 3-x , CH 3 H 3 PbI x Br 3-x , CH 3 H 3 PbI x Cl 3-x , CH 3 H 3 PbCl x Br 3-x , CH 3 H 3 PbI 3- xClx, CH 3 H 3 SnI 3 , CH 3 H 3 SnBr 3 , CH 3 H 3 SnCl 3 , CH 3 H 3 SnF 3 , CH 3 H 3 SnBrI 2 ,
• x is from 0 to 3.
• x may be from 0.05 to 2.95.
• x may be from 0.1 to 2.9, or from 0.5 to 2.5. In some cases, x is from 0.75 to 2.25, or from 1 to 2.
• the first crystalline compound may for instance be a perovskite compound selected from CH 3 H 3 Pbl3, CH 3 H 3 PbBr3, CFfc FfcPbCh, CH 3 H 3 PbF3, CFfc FfcPbBrli, CH 3 H 3 PbBrCl2, CH 3 H 3 PbIBr2, CFfc FfcPbICk, CH 3 H 3 PbClBr2, CFfe FfePbliCl, CH 3 H 3 Snl3, CH3NH3S11CI3, CH3 H3S11F3, CFfc FfcSnBrli,
• the first and/or second crystalline compound may be a perovskite compound selected from (CH3 H3)i- y (C 8 Hi 7 H3) y Pbl3, (CH 3 1 ⁇ 4)i- y (C 8 Hi 7 H3) y PbBr3, (CH 3 H 3 )i- y (C 8 Hi 7 H 3 ) y PbCl3, (CH 3 3 ⁇ 4)i- y (C 8 Hi 7 H3) y PbF3, (CH 3 H3)i- y (C 8 Hi 7 H3) y PbBrxl3-x, (CH 3 H3)i- y (C 8 Hi 7 H3) y PbBr x Cl3-x, (CH 3 H3)i- y (C 8 Hi 7 H3) y PbIxBr3-x, (CH 3 H 3 )i- y (C 8 Hi 7 H 3 ) y PbIxCl3-x, (CH 3 H3)i- y (C 8 Hi 7 H3) y Pb
• the first and/or second crystalline compound is a hexahalometallate compound.
• the first and/or second crystalline compound may for instance be a hexahalometallate compound which comprises at least one monocation, at least one metal or metalloid tetracation and at least one halide anion.
• the first and/or second crystalline compound may for instance be a hexahalometallate compound of formula (III):
• each of R 1 , R 2 , R 3 , R 4 , R 5 and R 6 is typically independently H, an unsubstituted Ci-10 alkyl group or phenyl.
• each monocation is independently selected from cations of formula ( R 1 4) + and (R 1 H3) + wherein R 1 is unsubstituted Ci-io alkyl.
• [A] may be a single monocation which is N(CH 3 )4 + or H 3 (CH 3 ) + .
• each metal or metalloid tetracation is selected from Ti 4+ , V 4+ , Mn 4+ , Fe 4+ , Co 4+ , Zr 4+ , Nb 4+ , Mo 4+ , Ru 4+ , Rh 4+ , Pd 4+ , Hf* + , Ta 4+ , W 4+ , Re 4+ , Os 4+ , Ir 4+ , Pt 4+ , Sn 4+ , Pb 4+ , Po 4+ , Si 4+ , Ge 4+ , and Te 4+ . More typically, each metal or metalloid tetracation is independently selected from Sn 4+ , Pb 4+ , Ge 4+ and Te 4+ . Preferably, the metal or metalloid tetra cation is Sn 4+ or Pb 4+ .
• each halide anion is typically independently selected from CI " , Br " and ⁇ . It has been found that the properties of the nanoparticles can be improved by adding a long chain alkylamine or alkylammonium halide.
• the nanoparticles may further comprise a C4-16 alkyl amine or a C4-16 alkyl ammonium halide.
• the nanoparticles forming the first and/or second plurality of nanoparticles further comprise an unsubstituted C4-16 alkyl ammonium halide.
• the unsubstituted C4-16 alkyl ammonium halide is often an octylammonium halide, for instance octylammonium iodide, bromide or chloride.
• the amount of the C4-16 alkyl ammonium halide is typically from 0.1 to 1.0 mol%, for instance from 0.4 to 0.8 mol%, relative to the at least one cation (e.g. (CH 3 H 3 ) + ) in crystalline compound.
• the amount of the C4-16 alkyl ammonium may be from 10 to 90 mol%, for instance from 30 to 90 mol%, from 40 to 80 mol%, or from 50 to 70 mol%, relative to the at least one cation in crystalline compound.
• the long chain alkylamine or alkylammonium halide may be dispersed within the nanoparticles or, preferably, may form a shell around the nanoparticles.
• the second crystalline compound may be as defined herein for the first crystalline compound.
• the second crystalline compound is often a perovskite compound of formula (I): [A][M][X] 3 (I) wherein: [A] is at least one monocation; [M] is at least one metal or metalloid dication; and [X] is at least one halide anion.
• the second crystalline compound is often a perovskite compound of formula (II): [A]M[X] 3 (II) wherein: [A] is two or more monocations; M is a single metal or metalloid dication; and [X] is at least one halide anion.
• the second crystalline compound is a layered perovskite compound of formula (Ha):
• the second crystalline compound may be a layered perovskite compound of formula (lib):
• first and second crystalline compounds are often different mixed cation perovskite compounds of formula (II):
• R 1 may be selected from methyl, ethyl, hexyl, heptyl octyl.
• the first and second crystalline compounds are different perovskite compounds of formula (I):
• the C4-16 alkyl amine or a C4-16 alkyl ammonium halide typically acts as a ligand and forms a coating on the nanoparticles.
• the nanoparticles typically have a particle size of from 1 to 500 nm.
• the nanoparticles have a particle size of from 2 to 150 nm, more preferably 4 to 50 nm.
• the first and second pluralities of nanoparticles may have a particle size of from 5 to 30 nm.
• Particle size is a well known term and refers (i) for a spherical particle, to the diameter of that spherical particle and (ii) for a non-spherical particle, to the diameter of a spherical particle having the same diameter as that non-spherical particle.
• the first plurality of nanoparticles and the second plurality of nanoparticles may take a number of different shapes. Often, some of the nanoparticles (e.g. greater than 50 wt% of the total nanoparticles) have an elongated shape, for instance a shape representing either a flattened rectangle or a rod. Thus, some of the particles may have a maximum length which is 50% greater than their minimum width. For instance, in the first and/or second plurality of nanoparticles, the nanoparticles may have a length of from 200 nm to 800 nm and a width of from 40 nm to 200 nm.
• the first and second plurality of nanoparticles may have a sphericity of less than or equal to 0.8, or less than or equal to 0.6.
• the first plurality of nanoparticles has a maximum photoluminescent emission of from 400 to 800 nm, preferably from 500 to 700 nm.
• the first plurality of nanoparticles may for instance have a maximum photoluminescent emission of from 500 to 575 nm and the second plurality of nanoparticles may have a maximum photoluminescent emission of from 575 to 650 nm.
• the first (and second) plurality of nanoparticles are disposed in the one or more matrix materials.
• a matrix material is any suitable material in which a plurality of nanoparticles can be suspended.
• the matrix material is typically solid.
• the matrix material is typically non- reactive in that it does not undergo a chemical reaction with the nanoparticles or any other part of the light emitting device (e.g. a metal component).
• the matrix material typically has a high transparency to light across a large proportion of the visible spectrum.
• the matrix material may be an inorganic material or an organic material.
• the matrix material is usually stable at temperatures up to 150°C or up to 100°C.
• the matrix material comprises a polymeric matrix material.
• a polymeric matrix material is a matrix material comprising a polymer.
• the polymeric matrix material typically comprises a polymer which is a polyalkene (e.g. polyethene, polypropene, polybutene, polymethylmethacrylate or polystyrene), a polyester (e.g. polyethylene terephthalate, polyhydroxybutyrate or polyethylene apidate), a polyurethane, a polycarbonate, a polyimide, a polyamide (e.g.
• the polymeric matrix material comprises a polymer selected from polymethylmethacrylate, polystyrene, polyurethane, a polycarbonate and a polyimide.
• the concentration of the first (second) plurality of nanoparticles in the matrix material is typically from 0.1 to 80 wt% relative to the combined weight of the matrix materials and first (second) plurality of nanoparticles.
• the concentration may for instance be from 1 to 40 wt%, or from 5 to 30 wt%.
• the use of nanoparticles of a crystalline material allows for the production of luminescent materials having a broad emission spectrum, particularly when a number of different types of crystalline compounds are used.
• the luminescent material may comprise nanoparticles of from two to ten different crystalline compounds as defined herein, for instance nanoparticles of three, four or five different crystalline compounds.
• the one or more matrix materials may be the same or different.
• the one or more matrix materials comprise one or more polymeric matrix materials, optionally wherein the one or more polymeric matrix materials are as defined above or selected from
• polymethylmethacrylate polystyrene, polyurethane, a polycarbonate, a polyimide, a polyamide or an epoxy resin.
• a luminescent material containing two or more pluralities of nanoparticles can either be essentially homogenous in that the two or more pluralities of nanoparticles are intermixed with each other or it can have a laminate structure comprising layers of matrix materials with one or more types of nanoparticles disposed therein.
• the luminescent material comprises: (a) a first layer comprising greater than 60 wt% of the first plurality of nanoparticles; and (b) a second layer comprising greater than 60 wt% of the second plurality of nanoparticles.
• the luminescent material may comprise a region which defines a first layer, and which region comprises 60 wt% of the total number of the first plurality of nanoparticles present in the luminescent material and a region which defines a second layer, and which region comprises 60 wt% of the total number of the second plurality of nanoparticles present in the luminescent material.
• the luminescent material comprises: (a) a first layer comprising greater than 80 wt% of the first plurality of nanoparticles; and (b) a second layer comprising greater than 80 wt% of the second plurality of nanoparticles.
• the first layer comprises 60 wt% or greater of nanoparticles and 40 wt% or less of matrix material, but rather that of the total mass of the first plurality of nanoparticles in the luminescent material as a whole, at least 60 wt% of those first nanoparticles are in the first layer (and consequently that at most 40% of those first nanoparticles are in the second layer).
• the luminescent material is formed from a plurality of layers.
• the first plurality of nanoparticles may form a first layer and the second plurality of nanoparticles may form a second layer.
• the luminescent material may comprise (a) a first layer comprising a matrix material and, disposed in the matrix material, the first plurality of nanoparticles and (b) a second layer comprising a matrix material and, disposed in the matrix material, the second plurality of nanoparticles.
• the first layer comprises less than 5 wt%, or less than 2 wt%, of the second plurality of nanoparticles and the second layer comprises less than 5 wt%, or less than 2 wt%, of the first plurality of nanoparticles.
• the first and second layer may be in direct contact or there may be an auxiliary layer between them, for instance a layer consisting essentially of a matrix material or a layer comprising an adhesive. Often, first and second layers are formed in direct contact.
• the first plurality of nanoparticles and the second plurality of nanoparticles are mutually interspersed within the matrix materials.
• the luminescent material may be formed by blending the first and second pluralities of nanoparticles in one or more matrix materials.
• the second crystalline compound may be as defined for the first crystalline compound herein.
• the first crystalline compound and second crystalline compound are different crystalline compounds.
• the first crystalline compound and the second crystalline compound are preferably identical to each other.
• [A], [M] and [X] may be as defined above.
• the first crystalline compound and the second crystalline compound are each different organic-inorganic metal halide perovskite compounds of formula (I).
• the first and second crystalline compounds may be different perovskite compounds selected from C3 ⁇ 4 H 3 PbI 3 , CH 3 H 3 PbBr 3 , CH 3 H 3 PbCl 3 , CH 3 H 3 PbF 3 , CH 3 H 3 PbBr x I 3-x , CH 3 H 3 PbBr x Cl 3 - x , CH 3 H 3 PbI x Br 3-x , CH 3 H 3 PbI x Cl 3-x ,
• x is from 0 to 3.
• x may be from 0.05 to 2.95.
• x may be from 0.1 to 2.9, or from 0.5 to 2.5. In some cases, x is from 0.75 to 2.25, or from 1 to 2.
• the first and second crystalline compounds are different perovskite compounds selected from CH 3 H 3 PbI 3 , CH 3 H 3 PbBr 3 , CH 3 H 3 PbCl 3 , CH 3 H 3 PbF 3 , CH 3 H 3 PbBrI 2 , CH 3 H 3 PbBrCl 2 , CH 3 H 3 PbIBr 2 , CH 3 H 3 PbICl 2 , CH 3 H 3 PbClBr 2 , CH 3 H 3 PbI 2 Cl, C3 ⁇ 4 H 3 SnI 3 , CH 3 H 3 SnBr 3 , CH 3 H 3 SnCl 3 , CH 3 H 3 SnF 3 , CH 3 H 3 SnBrI 2 ,
• the first and/or second plurality of nanoparticles may further comprise an unsubstituted C4-16 alkyl ammonium halide.
• the unsubstituted C4-16 alkyl ammonium halide is often an octylammonium halide, for instance octylammonium iodide, bromide or chloride.
• the alklyammonium halide may act as a ligand which forms a shell around each of the nanoparticles.
• the first crystalline compound may be CH 3 H 3 PbBr 3 and the second crystalline compound may be CH 3 H 3 PbBrI 2 or CH 3 H 3 PbI 3 .
• the first and second crystalline compounds are different perovskite compounds of formula Cs[M][X]3 or Rb[M][X] 3 , where [M] is at least one metal or metalloid dication as defined herein; and [X] is at least one halide anion as defined herein.
• the first and second crystalline compounds are different perovskite compounds of formula CsPbX 3 or RbPbX 3 .
• the nanoparticles typically further comprise a further organic cation, for instance formamidinium, guanidinium, unsubstituted C4-16 alkyl ammonium halide or phenylethylammonium.
• the unsubstituted C4-16 alkyl ammonium halide is often an octylammonium halide, for instance octylammonium iodide, bromide or chloride.
• the alklyammonium halide may act as a ligand which forms a shell around each of the nanoparticles.
• the two or more crystalline compounds In order to obtain a broad emission spectrum, it is typically necessary that the two or more crystalline compounds have different maximum photoluminescent emission wavelengths. Often, the difference between the wavelength of the maximum photoluminescent emission of the first plurality of nanoparticles and the wavelength of the maximum photoluminescent emission of the second plurality of nanoparticles is greater than or equal to 50 nm. The difference may be greater than or equal to 100 nm or greater than or equal to 150 nm.
• Nanoparticles of CH 3 NH 3 PbBr 3 have a maximum emission at about 520 nm
• nanoparticles of CH 3 NH 3 PbBrl2 have a maximum emission at about 678 nm
• nanoparticles of CH 3 NH 3 PbI 3 have a maximum emission at about 775 nm.
• the first plurality of nanoparticles may have a maximum photoluminescent emission wavelength of from 500 to 600 nm and the second plurality of nanoparticles may have a maximum photoluminescent emission wavelength of from 600 to 800 nm, for instance from 600 to 650 nm.
• the first plurality of nanoparticles and the second plurality of nanoparticles have an average particle size of from 2 to 100 nm, for instance from 5 to 50 nm.
• the average particle size of the first and, if present, second plurality of nanoparticles may be from 10 to 30 nm.
• the particle size of a nanoparticle is the diameter of a spherical particle having the same volume as the nanoparticle.
• the average particle size of a plurality of nanoparticles is typically the mass average particle size and may for instance be measured by laser diffraction.
• the luminescent material further comprises a third plurality of nanoparticles comprising a third crystalline compound disposed in the matrix materials, which third crystalline compound is a compound of formula [A] a [M]b[X] c , wherein: [A] is at least one cation; [M] is at least one metal or metalloid cation; [X] is at least one anion; a is an integer from 1 to 6; b is an integer from 1 to 6; and c is an integer from 1 to 18.
• the luminescent material further comprises a fourth plurality of nanoparticles comprising a fourth crystalline compound disposed in the matrix materials, which fourth crystalline compound is a compound of formula [A] a [M]b[X] c , wherein: [A] is at least one cation; [M] is at least one metal or metalloid cation; [X] is at least one anion; a is an integer from 1 to 6; b is an integer from 1 to 6; and c is an integer from 1 to 18.
• the third crystalline compound and/or the fourth crystalline compound may be as defined herein for the first crystalline compound.
• the first, second, third, and optionally fourth, crystalline compounds are all different crystalline compounds.
• the first, second, third and optionally fourth crystalline compounds may be different perovskite compounds selected from CH 3 H 3 PbI 3 , CH 3 H 3 PbBr3, CH 3 H 3 PbCl 3 , CH 3 H 3 PbF 3 , CH 3 H 3 PbBrI 2 , CH 3 H 3 PbBrCl 2 , CH 3 H 3 PbIBr 2 , CH 3 H 3 PbICl 2 ,
• the first crystalline compound may be CH 3 H 3 PbBr 3
• the second crystalline compound may be CH 3 H 3 PbBrI 2
• the third crystalline compound may be CH 3 H 3 PbI 3 .
• the third and, if present, fourth plurality of nanoparticles may be present as additional layers in the luminescent material or may be intermixed with the other nanoparticles.
• the luminescent material comprises: (c) a third layer comprising greater than 60% of the third plurality of nanoparticles; and optionally (d) a fourth layer comprising greater than 60% of the fourth plurality of nanoparticles.
• the third layer may comprise greater than 80%) of the third plurality of nanoparticles.
• the fourth layer may comprise greater than 80%> of the fourth plurality of nanoparticles.
• the third and fourth layers may be as define above for the first and second layers.
• the first plurality of nanoparticles, the second plurality of nanoparticles, the third plurality of nanoparticles, and optionally the fourth plurality of nanoparticles are mutually interspersed in the matrix materials.
• the nanoparticles useful in the invention may be produced by any suitable method.
• a precursor solution comprising a first precursor compound and a second precursor compound may be injected into a solvent (i.e. a non-coordinating solvent such as toluene) leading to precipitation of NCs of the crystalline material.
• a solvent i.e. a non-coordinating solvent such as toluene
• Perovskite NCs may be produced by using first precursor compound such as MAC1, MABr or MAI (where MA is
• N-crystals N-crystals
• oleic acid can also be added into the solvent (e.g. toluene). Typically from 20 mg to 60 mg of oleic acid is added in the 10 ml of the solvent (e.g. toluene) before the injection of the precursor solution.
• solvent e.g. toluene
• Mixed alkyl lead halide perovskite e.g MA(OA)PbX 3
• NCs may be produced by the following method. A longer chain length alkyl group is added into the precursor solution. This is then injected to a solvent such as toluene to lead to precipitation of the NCs.
• the NCs can also be synthesised by a solid-state reaction.
• the first and second precursor compounds are mixed, and the mixture is ground and then annealed, for instance at 100 °C for 20 min.
• the grinding and annealing process may be repeated 5-6 times to achieve homogenous mixture of NCs.
• the as-synthesised NCs may then be dispersed in toluene/or toluene-polymer.
• the dispersion of NCs in a solvent/polymer mixture may be disposed on a surface and heated to remove the solvent and leave a luminescent material comprising a polymer matrix with the NCs disposed therein.
• the invention also provides the use of a luminescent material as a phosphor in a light emitting device, which luminescent material comprises: one or more matrix materials, and, disposed in said one or more matrix materials, a first plurality of nanoparticles comprising a first crystalline compound, and a second plurality of nanoparticles comprising a second crystalline compound, wherein the first crystalline compound and the second crystalline compound are different compounds of formula [A] a [M]b[X] c , wherein: [A] is at least one cation; [M] is at least one metal or metalloid cation; [X] is at least one anion; a is an integer from 1 to 6; b is an integer from 1 to 6; and c is an integer from 1 to 18.
• a phosphor is a phosphorescent or fluorescent material which is used in light emitting devices to balance or change the colour of the light emitted by the device.
• the light emitting device may be as further defined herein.
• the invention provides a luminescent material comprising one or more matrix materials and disposed in said matrix materials:
• [A]a[M]b[X]c wherein: [A] is at least one cation; [M] is at least one metal or metalloid cation;
• [X] is at least one anion; a is an integer from 1 to 6; b is an integer from 1 to 6; and c is an integer from 1 to 18.
• the luminescent material may be as further defined herein.
• the first plurality of nanoparticles forms a first layer and the second plurality of nanoparticles forms a second layer.
• the luminescent material may comprise (a) a first layer comprising a matrix material and, disposed in the matrix material, the first plurality of nanoparticles and (b) a second layer comprising a matrix material and, disposed in the matrix material, the second plurality of nanoparticles.
• the first layer comprises less than 5 wt%, or less than 2 wt%, of the second plurality of nanoparticles and the second layer comprises less than 5 wt%, or less than 2 wt%, of the first plurality of nanoparticles Process for producing a light emitting device
• the invention provides a process for producing a light emitting device comprising a phosphor, which process comprises disposing a luminescent material as defined herein on a light source as defined herein.
• the luminescent material thus typically forms the phosphor.
• Disposing the luminescent material may comprises disposing a precursor solution comprising the luminescent material or disposing a solid layer of the precursor material.
• the process comprises combining a first plurality of nanoparticles comprising a first crystalline compound, a second plurality of nanoparticles comprising a second crystalline compound and one or more matrix materials, wherein said first and second crystalline compounds are different compounds of formula [A] a [M]b[X] c , wherein: [A] is at least one cation; [M] is at least one metal or metalloid cation; [X] is at least one anion; a is an integer from 1 to 6; b is an integer from 1 to 6; and c is an integer from 1 to 18.
• the luminescent material is a laminate material comprising a plurality of layers.
• the process typically comprises: (a) providing a first layer comprising a first matrix material and the first plurality of nanoparticles comprising a first crystalline compound; and (b) disposing on the first layer a second layer comprising a second matrix material and the second plurality of nanoparticles comprising a second crystalline compound.
• the first and second matrix materials may be the same or different and may be as defined herein.
• Disposing a layer comprising a matrix material and a plurality of nanoparticles comprising a crystalline compound typically comprises disposing a composition comprising a solvent, the plurality of nanoparticles and the matrix material and removing the solvent.
• the solvent is typically an organic solvent such as acetonitrile, toluene, DMSO or acetone. Removing the solvent typically comprises heating the composition to remove the solvent.
• disposing the layer may comprise simply disposing a composition comprising the plurality of nanoparticles and a precursor to the matrix material, and curing the precursor to the matrix material.
• the precursor to the matrix material may be a mixture of monomers or a polymer with a cross- linking agent.
• the process further comprises: (c) disposing on the second layer a third layer comprising a matrix material and a third plurality of nanoparticles comprising a third crystalline compound; and (d) optionally disposing on the third layer a fourth layer comprising a matrix material and a fourth plurality of nanoparticles comprising a fourth crystalline compound, wherein said third and fourth crystalline compounds are different compounds of formula [A] a [M]b[X] c , wherein: [A] is at least one cation; [M] is at least one metal or metalloid cation; [X] is at least one anion; a is an integer from 1 to 6; b is an integer from 1 to 6; and c is an integer from 1 to 18.
• the luminescent material may be as further defined herein.
• the commercially available lead source compounds i.e. PbCb, PbBr 2 and Pbl 2
• hydrogen halide acids HQ, HBr and HI
• Methylamine CH 3 H 2 41%)
• octylamine C 8 Hi 7 H 2
• Methyl ammonium iodide was synthesised by reacting typically 24 ml of Methylamine 33 wt.% in ethanol with 10 ml of Hydriiodic acid (57% in H 2 0) in 100 ml of C 2 H 5 OH. The reaction was carried out while vigorous stirring under ambient condition for 30-60 min.
• the reaction mixture was than subjected to rotary evaporator at 60 °C to remove the solvent, leading to the precipitation of a white/yellowish coloured methyl ammonium iodide (MAI) powder.
• MAI white/yellowish coloured methyl ammonium iodide
• the resulting product was then washed with diethylether several times to remove un-reacted reagents.
• the as-synthesised compound was then recrystallised with either C2H5OH or C2H5OH/CH3OCH3 solvent and dried in a vacuum furnace at 60 °C for 4 hours in order to get a purified white colour CH3 H3I (MAI) powder. Owing to its hygroscopic nature the purified MAI was stored under dry conditions.
• OAI octyl-ammonium-iodide
• OABr octyl-ammonium bromide
• OAC1 octyl-ammonium-chloride
• the length of alkyl group and halide group can be varied maintaining their required stoichiometric ratio to achieve crystals with varying size and photo-physical properties.
• MAPbBr3 precipitates out as nano-crystals (NCs).
• Ns nano-crystals
• MAPM3 perovskite nano-crystals were prepared by a similar method except for the solvent used to prepare the precursor solution, where a DMF and ACN solution mixture was used instead of pure DMF.
• the organic-inorganic perovskite can also be synthesised by solid-state reactions.
• An equimolar ratio of the alkyl-ammonium- halide and lead halide powders were mixed thoroughly under inert atmosphere.
• the mixture was ground and then annealed at 100 °C for 20 min.
• the grinding and annealing process was repeated 5-6 times to achieve a homogenous mixture.
• the perovskite already starts to form by mixing the reactants even without annealing. However the process of annealing helps to form and improve the stability of the perovskite crystals.
• the as synthesised perovskite crystallites are then dispersed in toluene/or toluene-polymer.
• Nano-crystal/Polymer film fabrication We demonstrate the fabrication of films of the nano-crystal (NCs) by mixing them with polymers (i.e PMMA) To fabricate perovskite NCs-polymer film, the as-synthesised perovskite NCs (in solution) were centrifuged for an hour at 7000 rpm (Fisher Scientific, AccuSpin 400) and blended with a desired amount of polymer.
• the nano-crystal and polymer concentration can be varied to achieve a certain level of absorbance and PLQE providing absolute flexibility in tuning the desired spectral region and intensity of the final PL emission.
• Photo-physical properties e.g. UV-Vis absorption, PL emission and quantum yield
• Photo-physical properties e.g. UV-Vis absorption, PL emission and quantum yield
• X-ray diffraction of the nano-crystal film was measured using Bruker D8 theta/theta (i.e. fixed sample) spectrometer with a position sensitive detector (LynxEye) and a standard detector (SC) with auto-absorber and graphite 2nd beam monochromator (Bragg Brentano para focusing geometry, reflection mode).
• TEM Transmission electron microscopy
• Jeol 4000EX 400 kV high resolution microscope.
• UV-vis absorption was measured on NCs/toluene dispersions in air using a commercial spectrophotometer (Varian Cary 300 UV- Vis, USA).
• the steady state PL was collected using a high-resolution mono-chromator and hybrid photomultiplier detector assembly (PMA Hybrid 40, PicoQuant GmbH).
• Time-resolved PL measurements were acquired using a time correlated single photon counting (TCSPC) setup (FluoTime 300, PicoQuant GmbH).
• TCSPC time correlated single photon counting
• NCs/toluene dispersion were photo-excited using 405 nm (for Br/I based perovskite and CI based perovskite respectively) laser head (LDH-P-C-510, PicoQuant GmbH) pulsed at frequencies of 1 MHz, with a pulse duration of 117 ps and fluence of -300 nJ/cm 2 .
• Photoluminescence quantum efficiency (PLQE) measurements were carried out using a 405 nm CW laser excitation source (Suwtech LDC-800) to illuminate a diluted NC colloidal sample in an integrating sphere (Oriel Instruments 70682NS), and the laser scatter and PL collected using a fiber-coupled detector (Ocean Optics MayaPro).
• a non-coordinating solvent e.g. toluene
• DMF can be used to prepare the precursor solution for CH 3 NH 3 PbBr 3 (MAPbBr 3 ) and CH 3 NH 3 PbCl 3 (MAPbCb) NCs.
• MAPbBr 3 CH 3 NH 3 PbCl 3
• MAPbI 3 CH 3 NH 3 PbI 3 NCs
• NCs with varying OA + /MA + composition i.e. MAPbBr 3
• NCs with neat MA + i.e. MAPbBr 3
• OA + group e.g. 0.6OA + /0.4MA +
• a lower symmetry cubic structure such as Pm-3m.
• MAPbBr 3 MAPbBr 3
• the PL spectra of MAPbBr 3 crystals exhibit similar PL peak maxima to the bulk MAPbBr 3 film, centered at around 531 nm.
• a systematic blue shift in PL emission peak could be explained by the quantum confinement effect in the nanostructure with the incorporation of OA + in the crystal structure.
• the minimum size of the crystals dimensions is on the order of 50nm. Previous studies have estimated the exciton Bohr radius of MAPbBr 3 to be 2- 6nm.
• the colloidal solution of the perovskite nano-crystals shows a compositional instability when they are mixed with other NCs with different halide anion. Therefore, any attempt to mix NCs with a distinct PL emission (excitation wavelength 425 nm) to achieve a wide PL emission may not give desirable results.
• FIG 5 top panel we show PL emission spectra of the neat Br (MApbBr 3 ) and I (MAPbI 3 ) based perovskite colloidal solution and also the mixed colloidal solution (V/V) of the two (i.e. MA(0.3OA)PbBr 3 and MA(0.3OA)PbI 3 ) NCs. The two colloidal solutions were mixed in a way to achieve a reasonably similar PL intensity.
• the neat Br and I based NCs has a single PL emission peak at 520 and 753 nm respectively.
• the mixed colloidal solution does show two PL emission spectrum, belonging to both Br and I based NCs but with a different maxima (at 551 and 704 nm respectively) then their respective parental peak positions.
• the obvious effect of their change in the PL emission spectrum is reflected in the obvious colour change of the mixed colloidal solution.
• Further to investigate the compositional stability of the mixed colloidal solution we measured PL emission continuously with constant excitation 425 nm.
• Figure 12 shows the emission spectra of the NC/polymer film, with (MA/OAPbI3) and (MA/OAPbBr3) polymer film emitting at 753 and 520 nm respectively (dotted lines).
• Blending the two NCs in the polymer matrix does not show any shifts in their respective emission peaks.
• NC/polymer thin film by blending them in an insulating and transparent matrix, (i.e. PMMA/ Polystyrene) and measure the PL emission spectra of the neat halide films and also the film of their respective mixture blends, shown in Figure 12.
• an insulating and transparent matrix i.e. PMMA/ Polystyrene
• the selective/broad emission can be realised either by fabricating a film of mixed
• This wide PL emission is a perfect precursor to generate efficient and tuneable white light emission from a perovskite NC/polymer composite film.
• we fabricated individual blue, green and red emitting films by employing perovskite NCs with Cl ⁇ , Br " and ⁇ halide group respectively.
• the PLQE of the OA/MAPbI 3 , OA/MAPbBr 3 and OA/MAPbCb films were 15, 25 and 10% respectively. The ease in which these flexible films emitting light at a selective spectral region can be synthesized provides enough opportunity to widen their applicability.
• commercial white LEDs for solid-state lighting are typically based on GaN blue LEDs with yellow-emitting Ce 3+ -doped Y3AI5O12 (YAG:Ce) phosphors.
• YAG:Ce yellow-emitting Ce 3+ -doped Y3AI5O12
• the conventional phosphor can be replaced with the blue/green/red-emitting perovskite NCs embedded in a polymer matrix.
• NCs chromaticity color coordinates
• CIE chromaticity color coordinates
• Figure 16 In principle it is possible to obtain any hue, colour and spectral composition from these perovskite NCs. We illustrate this by showing the CIE coordinates of the individual NC emission from all the PL spectra which we have shown in Figure 16. Notably, a combination of an appropriate fraction of these NCs into a single film or layered stack of films could position the CIE anywhere on the chart with broad spectral coverage. Spectra of other luminescent materials according to the invention comprising blends of different perovskite nanoparticles are shown in Figure 17.
• the perovskite nanocrystals (nanoparticles) dispersed in solution show a compositional instability when they are either mixed with perovskite nanocrystals containing different halide ion or by introducing halide ion through other sources.
• the nanocrystals do not retain their original composition in the presence of another halide ion rather show a strong tendency of undergoing ion-exchange in the crystal leading in to forming a completely new
• Figure 11 shows PL emission spectra of the neat MAo 7O Ao 3PbBr3 and MAo 7OA0 jPbL perovskite nanocrystals in solution and also the PL emission from a mixed NC solution containing a mixture from the two at an approximate 0.4:0.6 Volume to Volume ratio of the MAo 7O Ao 3PbBr3 to MAo 7OA0 jPbL solutions respectively.
• the volumetric ratio was chosen so to achieve a reasonably similar PL intensity from the two peaks.
• the neat MAo.70Ao.3PbBr3 and MAo 7OA0 jPbL NC solutions have a single PL emission peak at 520 and 753 nm respectively.
• the mixture of the two NC solutions does show two PL emission spectrum at these same wavelengths, but different PL peak position maxima at 551 and 704 nm. The measurements were performed ten minutes after mixing the solutions.
• the polystyrene beads (Acros Organics- 178890250) were added directly to each individual NC solution at a concentration of 220 mg/ml, and the two solutions were then mixed together and films were cast via depositing a small volume of the mixed solution onto a glass substrate and spin-coating to form a dry film.
• the PL emission spectra of the neat halide films and also the film of the mixed NC blend are shown in f Figure 12. Surprisingly, there is no significant shift in wavelength position of either the 525nm peak nor the 750nm peak. This strongly indicates that embedding the NCs in a polymer matrix inhibits Br/I ion exchange and hence stabilises the emission wavelength.
• the inventors do observe a slow reduction in the emission intensity of the MAo 7O Ao 3 PbI 3 peak at 750nm, which indicates a degradation of some form other than ion exchange.
• embedding the NCs in an insulating matrix appears to solve the problem of ion exchange, although further developments of the NCs and matrix may be required to achieve total stability of emission for long term light output.
• Figure 19 shows a further shift in the PL emission spectra of the mixed colloidal NC solution after several months. This shows that the ion exchange continues for a considerable amount of time.
• Example 4 Photoluminescence emission spectra of mixed halide perovskite NCs
• Figure 20 shows the PL intensity ((a) and (b)) and absorbance ((c) and (d)) for a variety of mixed halide MAPbX 3 perovskites.
• Figure 21 shows the PL intensity for a variety of mixed halide MAPbX 3 perovskites.
• Figure 22 shows the PL intensity for MA(OA)PbI 3 perovskites with varying OA/MA ratios.
• Figure 23 shows the PL intensity for MA(OA)PbCl 3
• perovskites with varying OA/MA ratios perovskites with varying OA/MA ratios.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Luminescent Compositions (AREA)
• Optical Filters (AREA)
• Led Device Packages (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (1)

Family

ID=54106726

Family Applications (1)

Country Status (7)

Cited By (16)

Families Citing this family (39)

Citations (1)

Family Cites Families (6)

• 2015
  • 2015-07-28 GB GBGB1513272.3A patent/GB201513272D0/en not_active Ceased
• 2016
  • 2016-07-27 JP JP2018504265A patent/JP6783296B2/ja active Active
  • 2016-07-27 US US15/748,062 patent/US10950761B2/en active Active
  • 2016-07-27 KR KR1020187005816A patent/KR102660265B1/ko active Active
  • 2016-07-27 CN CN201680044565.7A patent/CN108473865B/zh active Active
  • 2016-07-27 WO PCT/GB2016/052292 patent/WO2017017441A1/en not_active Ceased
  • 2016-07-27 EP EP16747564.9A patent/EP3328962B1/en active Active

Patent Citations (1)

Non-Patent Citations (3)

Also Published As

Similar Documents

Legal Events