for rare-earth ion cluster formation. Nonuniform distribution of erbium ions in silica host may lead to catastrophic increase in luminescence concentration quenching [2]. In contrast to fused silica, the solubility of lanthanides in phosphate glasses is much higher and rare-earth ion cluster formation is not typical for them.The particular focus of this work is the investigation of heavily erbium-doped glasses that may provide high gain per unit length. We have chosen several known multicomponent laser glasses (phosphate and silicate based) that have high capacity of rare-earth ion doping level (one or two order of magnitude higher than usually used fused silica-based glasses). Optical fibers on the base of such heavily activated glasses [3] as well as channel wave guides with high gain per unit length can enhance the development of compact photonic modules. Figure 1 illustrates the up-conversion process in Eractivated materials. Two interacting Er ions excited at 4 I 13/2 level give birth to one Er ion excited at 4 I 9/2 level. In oxide glasses, the excitations from this level relax very rapidly to the 4 I 11/2 state and then back to 4 I 13/2 level. Thus, one of the two excitations at the upper laser level is dissipated into heat. Usually, radiationless energy losses caused by upconversion processes are described by following equation where n is the excited ion density at the 4 I 13/2 level, τ-radiative lifetime, and α-nonlinear quenching parameter (up-conversion parameter). The value of α depends on spectroscopic properties of erbium ions and on their spatial distribution in definite glass host.The solution of this equation can be expressed in the following way:(1) dn/dt = −n/τ − αn 2(2) n(t) = n 0 exp (−t/τ )/[1 + αn 0 τ (1 − exp (−t/τ ))]Abstract Up-conversion can be the main mechanism of energy losses in laser glasses with high concentration of erbium ions. This investigation is devoted to the evaluation of up-conversion parameters in several phosphate and silicate Er-doped glasses. Analysis of the luminescent lifetime shortening at high excitation level has shown that the up-conversion parameters in different glasses can differ by an order of magnitude. The smallest up-conversion was observed in Ba crown silicate glass and Li-Ln-phosphate glass.