The rare earth ions are then selectively washed out by suitable complexing agent.

Particularly for active fibers, pure silica is usually not a very suitable host glass, because it exhibits a low solubility for rare earth ions.

The physical properties of chalcogenide glasses (high refractive index, low phonon energy, high nonlinearity) also make them ideal for incorporation into lasers and other active devices especially if doped with rare earth ions.

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The process is a radiationless, almost resonant transfer of energy between sites and depends on the relative concentrations of the rare earth ions.

As a single crystal structure doped with rare earth ions, it can be used as active laser medium.

The rare earth ions are then selectively washed out by suitable complexing agent, such as ammonium citrate or nitrilotracetate.

Since about 1990 the third generation TriPhosphors, three separate red, blue and green phosphors activated with rare earth ions and mixed in proportions to produce acceptable whites, have largely replaced halophosphors.

The active medium of the laser is optical fiber with its core doped with rare earth ions.

Paramagnetic rare earth ions have been used as particle sensors by sensing the spin flips of the paramagnetic atoms induced by heat absorbed in a low heat capacity material.