Practical limits of optical enhancement by metal nanoparticles

We develop a simple yet rigorous theory of the enhancement of optical absorption and emission by molecules placed in the vicinity of metal nanoparticles. Both enhancement effects exhibit strong dependence on the nanoparticle size. Using the example of Ag nanospheres embedded in GaN, we show that strong enhancement can be obtained only for those quantum dots, atoms, or molecules that are originally inefficient in absorbing as well as in emitting optical energy. We then discuss practical limits of enhancement.