Doped-nanoparticle photochromic heterostructures

A photochromic heterostructure comprising:

• (a) first semiconductor nanoparticles that have an average first-nanoparticle effective diameter from about 1 nanometer to about 20 nanometers, wherein said first semiconductor nanoparticles are not doped, and wherein said first semiconductor nanoparticles have a first bandgap energy;
• and
• (b) second semiconductor nanoparticles that have an average second-nanoparticle effective diameter from about 1 nanometer to about 60 nanometers, wherein said second semiconductor nanoparticles are doped with one or more transition metals, and wherein said second semiconductor nanoparticles have a second bandgap energy,
• wherein said first bandgap energy is lower than said second bandgap energy,
• wherein said first semiconductor nanoparticles and said second semiconductor nanoparticles are in physical contact with each other,
• and wherein said photochromic heterostructure comprises a plurality of core-shell structures, wherein each of said core-shell structures contains a core of said first semiconductor nanoparticles, and a shell of said second semiconductor nanoparticles.

A photochromic heterostructure comprising:

• (a) first semiconductor nanoparticles that have an average first-nanoparticle effective diameter from about 1 nanometer to about 20 nanometers, wherein said first semiconductor nanoparticles are not doped, and wherein said first semiconductor nanoparticles have a first bandgap energy;
• and
• (b) second semiconductor nanoparticles that have an average second-nanoparticle effective diameter from about 1 nanometer to about 60 nanometers, wherein said second semiconductor nanoparticles are doped with one or more transition metals, and wherein said second semiconductor nanoparticles have a second bandgap energy,
• wherein said first bandgap energy is lower than said second bandgap energy,
• wherein said first semiconductor nanoparticles and said second semiconductor nanoparticles are in physical contact with each other,
• and wherein said photochromic heterostructure comprises a plurality of core-shell structures, wherein each of said core-shell structures contains a core of said second semiconductor nanoparticles, and a shell of said first semiconductor nanoparticles.

A darkening article comprising:

• (A) a photochromic heterostructure comprising:
• first semiconductor nanoparticles that have an average first-nanoparticle effective diameter from about 1 nanometer to about 20 nanometers, wherein said first semiconductor nanoparticles are not doped, and wherein said first semiconductor nanoparticles have a first bandgap energy;
• and
• second semiconductor nanoparticles that have an average second-nanoparticle effective diameter from about 1 nanometer to about 60 nanometers, wherein said second semiconductor nanoparticles are doped with one or more transition metals, and wherein said second semiconductor nanoparticles have a second bandgap energy,
• wherein said first bandgap energy is lower than said second bandgap energy,
• and wherein said first semiconductor nanoparticles and said second semiconductor nanoparticles are in physical contact with each other, forming a photochromic nanoparticle pair that is (i) not a core-shell structure, or (ii) a core-shell structure containing a core of said first semiconductor nanoparticles and a shell of said second semiconductor nanoparticles, or (iii) a core-shell structure containing a core of said second semiconductor nanoparticles and a shell of said first semiconductor nanoparticles;
• (B) ligands bonded to said first semiconductor nanoparticles and/or to said second semiconductor nanoparticles;
• and
• (C) a matrix surrounding said first semiconductor nanoparticles and said second semiconductor nanoparticles,
• wherein said first semiconductor nanoparticles are capable of being photoexcited with light below the bandgap energy of said second semiconductor nanoparticles, to create a photoexcited hole,
• wherein said second semiconductor nanoparticles are capable of receiving said photoexcited hole in a dopant energy orbital, to create a new absorption,
• and wherein said photoexcited hole is trappable in said ligands and/or in said matrix, to reverse photochromism of said photochromic heterostructure.