Lithium tetraborate (Li₂B₄O₇) is mainly used in dosimetry as thermoluminescent material. This study is an overview of optical studies made with Tm doped Li₂B₄O₇ in glassy state. An energy level diagram of Tm³⁺ in Li₂B₄O₇ was obtained from the fluorescent spectra. Optical absorption measurements, between 2850 nm and 300 nm, showed bands due to the presence of Tm³⁺(4f¹²) in the glassy matrix because of its characteristic electronic transitions. Optical intensities determined at room temperature, for 455 nm absorption wavelength after different ⁶⁰Co gamma rays irradiation doses, show the reduction of Tm³⁺ to the Tm²⁺ state. The reconversion from Tm²⁺ to the Tm³⁺ states is shown by the fluorescence emission intensity at 455 nm due to a post-irradiation heating of the samples.