Optical properties of rare-earth ions

To put it simply, until the advent of the laser in 1962, rare earths were considered a scientific curiosity due to their position in the Mendeleev table. From then until 1988, rare-earth ion (REI) optics were dominated by the development of lasers pumped by "blackbody" lamps, essentially using the trivalent neodymium ion (Nd ³⁺ ). More specifically, YAG:Nd (Yttrium Aluminium Garnet: neodymium) lasers have proved their worth in many applications in physics laboratories, either in the continuous regime (CW) or in short pulses for the generation of harmonics or non-linear optical effects, but also in a more applied way for telemetry, welding, drilling and medicine.

Since 1988, a second period has seen the introduction of highly efficient monochromatic pumping sources such as III - V semiconductor lasers emitting in the near-infrared range. These sources, combined with the optical confinement provided by optical fibers, have led to the development of lasers and optical amplifiers based on other ions from the rare earth group, such as the erbium ion (Er ³⁺ ), which has been widely used in long-distance optical telecommunications since 1992. Since the early 2000s, these semiconductor lasers have also been used for optical pumping of ultra-intense laser chains (sub-picosecond pulses and multi-petawatt peak powers) based on transparent crystals and ceramics in the form of large-diameter plates, disks and fibers doped with the ytterbium ion (Yb ³⁺ ), for various applications such as particle production and acceleration. These same years also saw the emergence of very efficient III - N semiconductor lasers emitting in the blue range used to optically pump crystals and optical fibers doped with the praseodymium ion (Pr ³⁺ ) for the development of red-green-blue laser sources.

In parallel with the development of coherent light sources, rare earth ions are also very useful for the creation of new luminophores applied to lighting (low-energy lamps, LEDs), color television (LEDs and luminophores for direct-view or projection cathode ray tubes) or for X-ray converter-amplifiers for medical use and particle detection (scintillators).

Consequently, although numerous articles have been devoted to each of these developments and to rare-earth-doped materials in general