New isostructural compounds [Ln₇(3,5-DSB)₄(OH)₉(H₂O)₁₅]·4H₂O (Ln = Eu, Gd and Tb) (DSB = 3,5-disulfobenzoate), with excellent optical properties, have been obtained and studied. By combining the lanthanide cations with the DSB ligand the formation of a singular heptanuclear [Ln₇(OH)₉]⁺¹² metallic core secondary building unit (SBU) has been promoted. This core is defined as a bi-capped dicubane SBU, and is a 4-connected node in a bidimensional net with (4⁴·6²) topology. The highly efficient emission from the triplet state of the disulfobenzoic ligand in the Gd-MOF and the exponential temperature dependence of I_Triplet/I_Ln = I_o exp(−E_A/k_BT) allow the design of thermometers with different color ranges through the adequate multimetal combination that cover almost the whole visible spectrum and are useful in a wide temperature range (10–300 K) with unprecedented sensitivities up to 32% K⁻¹. The Eu-DSB and Tb-DSB MOFs present an optimum antenna effect, a temperature independent f–f emission temporal decay and, in spite of the close packing of the Ln ions inside the MOF, no concentration quenching. The external efficiency is drastically increased in MOFs with a combination of a few percent of Eu and/or Tb with Gd by means of radiative and non-radiative energy transfers from the Gd ions and Gd connected ligands.

The main properties of the ${\mathrm{Nd}}^{3+}\to {\mathrm{Yb}}^{3+}$ ${(}^4{F}_{3/2},{}^2{\overrightarrow{F_{7/2}}}^4{I}_{9/2},{}^2{F}_{5/2})$ energy transfer in yttrium aluminum borate nonlinear laser crystal have been studied. This host has been found especially suitable for efficient ${\mathrm{Nd}}^{3+}\to {\mathrm{Yb}}^{3+}$ energy transfer because of the good matching between phonon energy and the ${}^4{F}_{3/2}\left({\mathrm{Nd}}^{3+}{)-}^2{F}_{7/2}\right({\mathrm{Yb}}^{3+})$ energy gap (≅1000 ${\mathrm{cm}}^{\mathrm{-}1}$). Energy-transfer probabilities in excess of 65% have been obtained for a ${\mathrm{Nd}}^{3+}$ (10 at. %) and ${\mathrm{Yb}}^{3+}$ (5 at. %) codoped sample. The influence of both crystal temperature and ${\mathrm{Nd}}^{3+}$ concentration on the transfer probability has been investigated. In the 15–350 K range the ${\mathrm{Nd}}^{3+}\to {\mathrm{Yb}}^{3+}$ energy-transfer efficiency increases with temperature, whereas for crystal temperatures above 350 K the ${\mathrm{Nd}}^{3+}\leftarrow {\mathrm{Yb}}^{3+}$ back transfer is activated, leading to a decrease in the effective ${\mathrm{Nd}}^{3+}\to {\mathrm{Yb}}^{3+}$ energy-transfer probability. The analysis of the decay curves obtained after pulsed excitation has been used to determine the multipole character of the ${\mathrm{Nd}}^{3+}-{\mathrm{Yb}}^{3+}$ interaction. The donor-acceptor energy-transfer microparameter was determined $\left[C_{\mathrm{DA}}\right({\mathrm{Nd}}^{3+}\to {\mathrm{Yb}}^{3+})\cong 18\times {10}^{-39}{\mathrm{cm}}^6/\mathrm{s}],$ and compared to those obtained for other ${\mathrm{Nd}}^{3+}-{\mathrm{Yb}}^{3+}$ co-doped materials.

Stable continuous-wave laser action in the near-infrared and in the green spectral region has been obtained in a self-frequency doubling solid-state laser, the ${\mathrm{Yb}}^{\mathrm{3+}}{\mathrm{:MgO:LiNbO}}_{\mathrm{3}}$ nonlinear crystal. By pumping with a Ti:sapphire laser and using a nearly concentric cavity, laser action at 1.06 μm was achieved with an absorbed power threshold of 101 mW and efficiency around 47%. As much as 60 mW of self-frequency-doubled radiation at 530 nm was also obtained with absorbed pump powers of 800 mW in critical cavity alignment. Efficient laser action was also obtained in the near-infrared region under pumping with diode laser.

In this Letter we have used the optical pump induced thermal loading to drive a ${\mathrm{Nd}}^{3+}$ doped ${\mathrm{Sr}}_{0.47}{\mathrm{Ba}}_{0.53}({\mathrm{NbO}}_3{)}_2$ laser crystal during laser operation through its ferroelectric phase transition. We demonstrate that lasing is possible below, at, and above phase transition. For temperatures close to $T_c$ ($\approx 105°\mathrm{C}$) the spatial distribution of laser radiation is remarkably affected. This feature, which leads to a laser gain depression, can be explained in terms of the strong temperature dependence of the thermo-optic coefficient during phase transition. Additionally, the visible radiation generated by intracavity self-frequency doubling disappears when the phase transition is undergone, showing a bistable behavior. The results provide fundamental information on physical parameters along the phase transition and will stimulate further work in the fields of nonlinear optics, optical switching, and data storage.

The laser performance of the nonlinear ${\mathrm{Yb}}^{\mathrm{3+}}{\mathrm{:MgO:LiNbO}}_{\mathrm{3}}$ crystal is assessed under Ti:sapphire laser pumping. Spectral properties related to infrared laser action such as the emission and absorption cross sections have been evaluated. Different crystallographic configurations have been used. Laser oscillation in the near infrared region has been observed along the crystallographic $c$ axis and along the type I phase matching direction for infrared to green generation. High slope efficiency in the infrared region (62%) and the possibility of low laser thresholds (14.7 mW) are demonstrated. By using a birefringent filter, broadband tuning from 1030 to 1070 nm is obtained in this system. In addition, 58 mW of green power by self-frequency doubling of infrared laser emission is achieved, revealing the potential of ${\mathrm{LiNbO}}_{\mathrm{3}}\mathrm{:MgO}$ as a self-frequency-doubling material.