Layered photochromic composition and device
An optical power-limiting passive (self-adaptive) device and method for limiting optical power transmission in lenses and windows, using layers of different photochromic compositions that exploit the full solar ultraviolet (UV) and short visible light spectrum. While a typical single photochromic material is activated by a UV band of wavelengths, e.g. 340 to 380 nm, adding a layer of photochromic material that is activated by an additional band of wavelengths, e.g., 380 to 420 nm, allows the efficient use of a wider band of solar UV and short visible light, e.g., 340 to 420 nm, thus enhancing the photochromic response to solar light.
1. A layered photochromic composition for providing protection from impinging solar light that includes ultraviolet light, said composition comprising
first and second layers of photochromic material, the first layer receiving said solar light and the second layer receiving light from the first layer,
said first layer having an outer surface receiving said solar light and an inner surface facing said second layer, said first layer containing a first photochromic material that is reversibly activated by impinging ultraviolet light having wavelengths within a first activation spectral band, and
said second layer having a first surface facing the inner surface of said first layer and a second surface facing away from said first layer, said second layer containing a second photochromic material that is reversibly activated by ultraviolet light received from said first layer and having wavelengths within a second activation spectral band that is non-overlapping or only partially overlapping with said first activation spectral band, said second photochromic material being more susceptible to fatigue from exposure to ultraviolet light than said first photochromic material,
wherein the absorption of ultraviolet light by said first layer reduces the amount of ultraviolet light that reaches said second layer.
2. The layered photochromic composition of claim 1 in which each of said layers includes a matrix material containing a photochromic dye.
3. The layered photochromic composition of claim 1 in which each of said photochromic materials comprises at least one organic material selected from the group consisting of pyrans, oxazines, fulgides, fulgimides, diarylethenes, in monomeric or polymeric ungelled solution or chemically bonded.
4. The layered photochromic composition of claim 1 in which each of said photochromic materials comprises at least one inorganic material selected from the group consisting of crystallites of silver halides, cadmium halide and copper halide.
5. The layered photochromic composition of claim 2 in which the matrix materials are organic-based: polymer film, polymerizable compositions, transparent adhesives, or inorganic-based: mineral glass, sol-gel, other window based material, and an inorganic-organic composite.
6. The layered photochromic composition of claim 1 in which each of said layers has a temperature response that is different from the temperature response of the other layers.
7. The layered photochromic composition of claim 1 which includes a tinted layer for color correction.
8. A method of providing protection from impinging solar light using a layered photochromic material, said method comprising
receiving the solar light in a first layer having an outer surface receiving the solar light and containing a first photochromic material that is reversibly activated by impinging ultraviolet light having wavelengths within a first activation spectral band,
receiving the light that is transmitted through said first layer in a second layer containing a second photochromic material that is reversibly activated by ultraviolet light received from said first layer and having wavelengths within a second activation spectral band that is non-overlapping or only partially overlapping with said first activation spectral band, said second photochromic material being more susceptible to fatigue from exposure to ultraviolet light than said first photochromic material,
wherein the absorption of ultraviolet light by said first layer reduces the amount of ultraviolet light that reaches said second layer.
9. The method of claim 8 in which each of said layers includes a matrix material containing a photochromic dye.
10. The method of claim 8 in which each of said photochromic materials comprises at least one organic material selected from the group consisting of pyrans, oxazines, fulgides, fulgimides, diarylethenes, in monomeric or polymeric ungelled solution or chemically bonded.
11. The method of claim 8 in which each of said photochromic materials comprises at least one inorganic material selected from the group consisting of crystallites of silver halides, cadmium halide and copper halide.
12. The method of claim 9 in which the matrix materials are organic-based: polymer film, polymerizable compositions, transparent adhesives, or inorganic-based: mineral glass, sol-gel, other window based material, and an inorganic-organic composite.
13. The method of claim 8 in which each of said layers has a temperature response that is different from the temperature response of the other layers.
14. The method of claim 8 which includes a tinted layer for color correction.