Isolated ions and nanoparticles are well understood, and the quantum mechanics that describes their behavior is well developed. Thus, these objects are ideal as probes for systems whose properties are poorly understood. This thesis is concerned with developing an understanding of the electronic and optical properties of rare earth ions and semiconductor nanoparticles and using them as probes. Particularly, we use what is understood about these probes to remove the effects of well understood processes from experimental data. The resulting processed data contains information about the system being probed via that system's influence on the probe.

This thesis presents two experimental studies. The first is the investigation of the presence of localized surface plasmons on a wrinkled gold-palladium surface. We deposit semiconductor nanoparticles on this surface and subsequently measure the optical properties of the nanoparticles to identify signatures of plasmon-nanoparticle coupling. We then discuss this coupling in the context of solar energy harvesting. The second study is an investigation of the geometrically frustrated magnetic phase (spin liquid) of gadolinium gallium garnet. We dope this crystal with a rare earth, trivalent neodymium, which is optically active. We then track the infrared emission spectrum of the dopant for signatures of neodymium/spin-liquid coupling. We then discuss the optical effects measured in the context of measuring and manipulating the spin-protectorate magnetic phase of gadolinium gallium garnet.