UV-reflective structural color
The present invention discloses a non-quarter wave multilayer structure having a plurality of alternating low index of refraction material stacks and high index of refraction material stacks. The plurality of alternating stacks can reflect electromagnetic radiation in the ultraviolet region and a narrow band of electromagnetic radiation in the visible region. The non-quarter wave multilayer structure, i.e. n L d L ≠n H d H ≠λ 0 /4, can be expressed as [A 0.5 qH pL(qH pL) N 0.5 qH G], where q and p are multipliers to the quarter-wave thicknesses of high and low refractive index material, respectively, H is the quarter-wave thickness of the high refracting index material; L is the quarter-wave thickness of the low refracting index material; N represents the total number of layers between bounding half layers of high index of refraction material (0.5 qH); G represents a substrate and A represents air.
1. A multilayer structure comprising:
a plurality of alternating layers of a low index of refraction material and a high index of refraction material;
said plurality of alternating layers of said low index of refraction material and said high index of refraction material reflecting electromagnetic radiation in the ultraviolet region and a narrow band of electromagnetic radiation in the visible region;
said plurality of alternating layers of said low index of refraction material and said high index of refraction material having a layered structure described by [A 0.5 qH pL (qH pL) N 0.5 qH G], where:
A represents air;
q is a multiplier of a quarter-wave thickness of said high index of refraction material;
H is the quarter wave thickness of the high refracting index material for a given wavelength λ 0 ;
p is a multiplier of a quarter-wave thickness of said low index of refraction material;
L is the quarter-wave thickness of the low refracting index material for said given wavelength λ 0 ;
N represents the total number of layers between bounding half layers of said high index of refraction material; and
G represents a substrate.
2. The multilayer structure of claim 1 , wherein said plurality of alternating layers of said low index of refraction material and said high index of refraction material each have a non-quarter wave thickness.
3. The multilayer structure of claim 1 , wherein said plurality of alternating layers of said low index of refraction material and said high index of refraction material reflect more than 70% of said electromagnetic radiation in the ultraviolet region and more than 60% of said narrow band of electromagnetic radiation in the visible region.
4. The multilayer structure of claim 1 , wherein said plurality of alternating layers of said low index of refraction material and said high index of refraction material are made by a layer-by-layer process.
5. The multilayer structure of claim 4 , wherein said low index of refraction material is made from SiO 2 nanoparticles and said high index of refraction material is made from TiO 2 nanoparticles.
6. The multilayer structure of claim 1 , wherein said plurality of alternating layers of said low index of refraction material and said high index of refraction material are in the form of a flake.
7. The multilayer structure of claim 6 , wherein said flake is a pigment for a paint.
8. The multilayer structure of claim 7 , wherein said paint is an ultraviolet reflective structural color.
9. A process for making a multilayer structure that is an ultraviolet-reflective structural color, the process comprising:
providing a low index of refraction material and a high index of refraction material;
fabricating a first layer from the low index of refraction material;
fabricating a second layer from the high index of refraction material adjacent to and in contact with the first layer;
the first layer and the second layer having a thickness of pL and qH, respectively, and being part of an ultraviolet-reflective structural color layered structure described by [A 0.5 qH pL (qH pL) N 0.5 qH G], where:
A represents air;
q is a multiplier of a quarter-wave thickness of said high index of refraction material;
H is the quarter wave thickness of the high refracting index material for a given wavelength λ 0 ;
p is a multiplier of a quarter-wave thickness of said low index of refraction material;
L is the quarter-wave thickness of the low refracting index material for said given wavelength λ 0 ;
N represents the total number of layers between bounding half layers of said high index of refraction material; and
G represents a substrate.
10. The process of claim 9 , further including fabricating a plurality of alternating first layers and second layers.
11. The process of claim 10 , wherein the plurality of first layers and second layers are fabricated using layer-by-layer processing.