Studies of absorption and luminescence spectra, and luminescence decay times of the intrashell f–f transitionsof Y b3 + ions in bulk orthophosphates at different temperatures and at highhydrostatic pressures are presented. The spectroscopic properties ofY0.99Y b0.01PO4 crystal with a tetragonal zircon structure andGd0.99Y b0.01PO4 andLa0.95Y b0.05PO4 crystals with a monoclinic monazite structure are compared. Experiments atambient pressure were performed at temperatures from 10 to 295 K whereasmeasurements at high pressure were performed in a diamond-anvil cell at 10 K with apressure up to 160 kbar. The results reveal a high thermal and pressure stabilityof the optical properties of the examined crystals as well as the dependence ofY b3 + emission properties on the local symmetry of the site occupied by the ytterbium dopant.