Research on upconversion nanoparticles, including those with core-shell hybrids and rare-earth doping, is being explored for various applications. The studies involve the synthesis, optimization, and use of these nanoparticles in fields such as optogenetics, bioimaging, and photoluminescence. The nanoparticles' properties, including upconversion enhancement and luminescence, are being investigated and modified through different designs and surface layers.