Ultra-high sensitivity sensors can be achieved with optically levitated particles in ultra-high vacuum (UHV). Trapped particles act as high-Q harmonic oscillators, whose amplitude, position, and frequency can be monitored to provide high sensitivity measurements of the particle’s acceleration. Larger particles (10-30 microns in diameter) provide higher sensitivity, but they are difficult to trap in UHV without particle loss. To overcome the radiometric forces that lead to particle loss, rare earth (RE) ion dopants can be incorporated into the particles to enable solid-state laser cooling of the particle’s internal temperature. The laser used for optical trapping can be tuned to a wavelength on the lower energy side of the ion absorption band, and thus also serve as the pump laser for solid-state laser cooling. Internal cooling occurs when the average energy of the photons emitted is larger than the average energy of the photons absorbed. Ions will rapidly thermalize while in the ground and the excited states to create the energy difference. Solid-state laser cooling has been realized in bulk host materials and is well understood. This technique of internal cooling for reducing loss pressure is currently being tested.