Enhanced photoluminescence

A plasmonic apparatus comprising:

• a substrate having a first negative-permittivity layer comprising a first plasmonic surface;
• a plasmonic nanoparticle having a base with a second negative-permittivity layer comprising a second plasmonic surface;
• a dielectric-filled gap between the first plasmonic surface and the second plasmonic surface,
• a plasmonic cavity created by an assembly of the first plasmonic surface, the second plasmonic surface, and the dielectric-filed gap, and having a spectrally separated first fundamental resonant cavity wavelength λ1 and second resonant cavity wavelength λ2 that is a 3rd harmonic of the first fundamental resonant cavity wavelength λ1;
• and
• a plurality of fluorescent particles located in the dielectric-filled gap, each fluorescent particle of the plurality of fluorescent particles having an absorption spectrum including the first fundamental resonant cavity wavelength λ1 and a 3rd harmonic nonlinearity with an emission spectrum including the second resonant cavity wavelength λ2.

A method comprising:

• directing a first electromagnetic beam that includes a first wavelength λ1 at a plasmonic apparatus;
• and
• emitting a second electromagnetic beam at a second wavelength λ2 from the plasmonic apparatus, the second electromagnetic beam having a higher quantum energy level than the first electromagnetic beam,
• the plasmonic apparatus comprising:
• a substrate having a first negative-permittivity layer comprising a first plasmonic surface;
• a plasmonic nanoparticle having a base with a second negative-permittivity layer comprising a second plasmonic surface;
• a dielectric-filled gap between the first plasmonic surface and the second plasmonic surface;
• a plasmonic cavity created by an assembly of the first plasmonic surface, the second plasmonic surface, and the dielectric-filled gap, and having a spectrally separated first fundamental resonant cavity wavelength λ1 and second fundamental resonant cavity wavelength λ2;
• and
• a plurality of fluorescent particles located in the dielectric-filled gap, each fluorescent particle of the plurality of fluorescent particles having an absorption spectrum including the first fundamental resonant cavity wavelength λ1 and an emission spectrum including the second fundamental resonant cavity wavelength λ2.