Results are presented here towards robust room-temperature SPSs based on fluorescence in nanocrystals: colloidal
quantum dots, color-center diamonds and doped with trivalent rare-earth ions (TR<sup>3+</sup>). We used cholesteric chiral
photonic bandgap and Bragg-reflector microcavities for single emitter fluorescence enhancement. We also developed
plasmonic bowtie nanoantennas and 2D-Si-photonic bandgap microcavities. The paper also provides short outlines of
other technologies for room-temperature single-photon sources.
Upconversion in rare-earth ions is a sequential multiphoton process that efficiently converts two or more low-energy
photons, which are generally near infrared (NIR) light, to produce anti-Stokes emission of a higher energy photon (e.g.,
NIR, visible, ultraviolet) using continuous-wave (cw) diode laser excitation. Here, we show the engineering of novel,
efficient, and biocompatible NIR<sub>in</sub>-to-NIR<sub>out</sub> upconversion nanoparticles for biomedical imaging with both excitation and
emission being within the “optical transparency window” of tissues. The small animal whole-body imaging with
exceptional contrast (signal-to-noise ratio of 310) was shown using BALB/c mice intravenously injected with aqueously
dispersed nanoparticles. An imaging depth as deep as 3.2-cm was successfully demonstrated using thick animal tissue
(pork) under cw laser excitation at 980 nm.