Yb³⁺ doped materials are recently attracting much attention as potential solid state laser materials due to the particular characteristics provided by the energy level scheme of this ion. Among others, its special electronic configuration makes the 4f electrons less shielded than in other ions of the lanthanide series, showing a higher tendency to interact with the lattice and neighbour ions. Thus, laser action from Yb³⁺ doped systems shows several interesting properties such as the possibility of a certain tunability range.
The most relevant results obtained in the Yb³⁺:LiNbO₃ system will be shown.
On one part, stable laser action in the near infrared region and coherent green radiation by self-frequency doubling have been obtained simultaneously. The results have been obtained for single domain and PPLN crystals.
On the other hand, and from the fundamental viewpoint, under near infrared excitation cooperative green emission is obtained from Yb³⁺ ions in this system due to a relatively strong (dipole-dipole, dipole-quadrupole) interaction among 4f electrons of two neighbour Yb³⁺ ions. Their simultaneous de-excitation produces one visible photon of double the energy of the infrared one. By using the cooperative emission as a probe it is possible to determine the distribution of Yb³⁺ ions in the host matrix and predict the presence of Yb³⁺ pairs in the system.
Additionally, intrinsic optical bistability has been observed in materials exhibiting cooperative luminescence. Accordingly, preliminary results on the hysteretic behaviour of the luminescence from Yb³⁺ (in the near infrared and in the green region of the spectrum) as a function of the excitation intensity will be also presented for Yb³⁺ activated LiNbO₃ crystals.

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