The spectroscopic properties of P2O5–Y2O3–Er2O3 and P2O5–Li2O–Al2O3–Y2O3–Er2O3 ultraphosphate glasses have been investigated. The concentration quenching rates of Er3+ in these two systems are lower compared with those in other oxide glasses. The spectral broadening of the measured fluorescence of 83.33P2O5–(16.67-x)Er2O3–xY2O3 (x=0.1 and 16.67) was observed by increasing temperature. Meanwhile, the lifetime of the 4I13/2 level shows the temperature dependence with increasing temperature, ascribed to the possible thermalization of higher-lying sublevels of the 4I13/2 level with faster radiative rates and the effect of radiation trapping. At room temperature, the deformation of the emission spectrum line shape has been observed with the increase of Er2O3 concentration due to the reabsorption effect. The 1.5-μm-amplification characteristics of P2O5–Y2O3–Er2O3 ultraphosphate glasses have been predicted from the calculated gain spectra at different pump powers. © 2001 American Institute of Physics.