US Patent 7798922 - Athletic field markings with quantum dots

http://ip.com/patent/US7798922

This patent teaches using quantum dots to form photoluminescent lines that distinguish football markings and soccer markings depending on exterior lighting. Claim 1 reads:

1. A method for selectively marking a surface, the method comprising:

marking the surface with lines of a first material containing quantum dots having a first absorption characteristic and a first emission characteristic; and

selectively illuminating the surface with radiation consistent with the first absorption characteristic to cause the lines of the first material to display the first emission characteristic.