In recent years, optical materials containing rare earth ions (lanthanides)gained a special interest, being an essential aspect of so-called quantum cutting (multi-photon) phosphors for high-efficiency Hg-free fluorescent lamps and plasma display panels, as well as of new scintillators with faster emission and higher conversion efficiency for positron emission tomography. For most of the trivalent rare earth ions the radiative 5d-4f transitions occur in the VUV spectral range and for their experimental studies it is necessary to apply the technique of VUV spectroscopy, preferably in combination with synchrotron radiation. Up to recently, luminescence from trivalent rare earth ions in VUV has been detected only from Nd3+, Er3+, and Tm3+. However, our studies have shown that 5d-4f luminescence in deep VUV region (hv ~10 eV) is also observed from Gd3+ and Lu3+ ions doped into some fluoride hosts with sufficiently wide energy band gaps. The results of the studies with high spectral and time resolution of different rare earth containing materials will be discussed, the trends in optical properties of rare earth ions throughout the lanthanide series will be analyzed and possible applications of rare earth based phosphors will be considered.