Non-invasive energy upconversion methods and systems

Products, compositions, systems, and methods for modifying a target structure. The methods may be performed in a non-invasive manner by placing a nanoparticle having a metallic shell on at least a fraction of a surface in a vicinity of a target structure in a subject and applying an initiation energy thus producing an effect on or change to the target structure directly or via a modulation agent. The nanoparticle is configured, upon exposure to a first wavelength λ1, to generate a second wavelength λ2 of radiation having a higher energy than the first wavelength λ1. The methods may further be performed by application of an initiation energy to activate a photoactivatable agent directly or via an energy modulation agent, optionally in the presence of one or more plasmonics active agents, thus producing an effect on or change to the target structure.