We investigate the cross relaxation parameter of Tm3+ ions in tellurite glasses over a wide range of concentrations: from
0.36 mol% up to 10 mol%. We propose a new measurement approach based on monitoring the steady-state emission
spectra. The proposed method is very simple and allows to measure even very highly doped samples. The crossrelaxation
parameter shows a linear dependence with respect to dopant concentration over the full investigated interval
and the measured slope is 1.81x10-17 cm3 s-1 mol%-1. The linear dependence suggests a dipole-dipole interaction.
In this paper, we present our recent investigation of highly doped Tm<sup>3+</sup> tellurite glass. The optical properties of series of
tellurite glass samples (75 mol % TeO<sub>2</sub> - 20 mol ZnO - 5 mol % Na<sub>2</sub>O) highly doped with Tm<sup>3+</sup> ions were reported and
discussed. An exhaustive set of samples from low concentration to very high have been used in this study. Cross
relaxation process has been studied and cross-relaxation parameter has been calculated.
We performed extensive spectroscopy of tellurite glasses doped with high concentration of Tm ions for laser emission at
around 2 micron wavelength. The aim of the work is to develop a glass suitable for single-frequency fiber laser. In fact
such a kind of laser require the use of short cavity length and therefore high gain per unit length medium. Tellurite
glasses allows high-doping concentration and are therefore an excellent candidate. In these paper we review our recent
results. In particular we address the optical and thermo-mechanical properties of several tellurite glasses
(75mol%Te02.20mol%ZnO. 5mol%Na2O) with Tm<sup>3+</sup> doping up to 111,564 ppm.