Structural and spectroscopic properties of Sm3+-doped alkali silicate glasses were investigated after densification at 7.7 GPa in a large volume high pressure apparatus. The glass composition was 33M2O + 66SiO2 + 1Sm2O3, where M = Li, Na or K. Raman and infrared spectroscopy revealed small changes in the vibrational modes dependent on the alkali ion. Irreversible changes were observed in the optical absorption spectra of Sm3+ ions. The Judd–Ofelt parameters were calculated to evaluate the effect of pressure on the local field. For lithium silicate, Ω2 parameter increased, suggesting the densification increased the local asymmetry of the Sm3+ environment. For sodium silicate, this parameter decreased considerably, suggesting the opposite effect on the local field, while for potassium silicate, it remained practically unchanged. The changes induced by high pressure are probably due to the irreversible changes in the distances and bond angles between the rare earth ion and the ligands.