Er Glass 2940nm Lasers using Yb–Er phosphate glass with 3×1019 and 5.6×1019 cm−3 of Er concentrations are investigated. It is concluded that up conversion plays significant role even for so low doped glasses. Development of new pumping Er glass laser diodes, with veryhigh output power has increased the requirements for mechanical, optical, and thermal resistance of new active media. Higher concentrations of dopants are required, especially fordiode pumped lasers. Intensive works have been made in order to find a new type of laser glasses with very high thermal resistance and optimal concentrations of dopants. At the General Physics Institute, laser materialsand technology research centre Russian Academy of Sciences in Moscow, under Professor Denker leadership, two new types of erbium glasses were developed. One of them is concentrated Yb−Er laser glass (GLASS) with concentration of ytterbium ions as high as 4.2×1021 cm–3. Passive Q switching of an Er:glass laser with the pulse width varying between 14 and 80 ns has been demonstrated, using three resonator er glass mirror samples with temperature‐dependent reflectivity and differing in the reflectivity contrast. Broad band operating characteristics of Q Switch Laser Er glass provide Q switching over a wide range of wavelengths. In addition, mode‐locked pulses with much shorter time scales have been observed, due to exciton formation and recombination. A simple criterion is derived for the allowable ambient temperatures at which the Q switching operates effectively. A simple relation has also been found relating the duration of the Q‐switched pulse to the contrast in reflectivities of the two er glass mirror phases.