High pressure effect in the near-infrared emission of Nd³⁺-doped alkali silicate glasses

The effect of high pressure (7.7 GPa) densification on the absorption and near-infrared emission of Nd-doped lithium, sodium and potassium disilicate glasses was investigated. Judd-Ofelt parameters Ω_λ (λ = 2, 4 and 6) were calculated from the absorption spectra, before and after densification of glasses, indicating that the irreversible structural changes induced by pressure increased the symmetry of the Nd-O bonding. Density and refractive index of the glasses also increased, probably related to the close packing of SiO₄ tetrahedra during densification. The magnitude of the splitting due to the Stark effect was larger for potassium silicate, before and after densification. The radiative transition probabilities of the hypersensitive transition for sodium and potassium silicate increased after densification while the radiative lifetime decreased. For lithium silicate, the opposite behavior was observed. The experimental results corroborate the influence of alkali ion and densification on the luminescence properties of Nd-doped alkali silicate glasses.