Photoluminescence in pulsed-laser deposited GeGaSbS:Er films

The complex dielectric function, the Er3+ Stokes emission at ≈1540 nm and the upconversion photoluminescence at ≈990 nm of pulsed-laser deposited thin-film GeGaSbS:Er3+ are studied. The linear-refractive-index dispersion is obtained by fitting spectroscopic ellipsometry data to the Sellmeier and the Cody-Lorentz parametrizations. The former model is used to calculate nonlinear refractive index. The Stokes emission intensity at ≈1540 nm, originating from the Er3+: 4I13/2 → 4I15/2 transition under a 980 nm pumping, diminishes with increasing refractive index and decreasing optical-bandgap energy of the films. An attempt to relate differences in the optical and photoluminescence properties to the atomic structure elucidated from Raman spectra analysis is presented. The emission probability is highest for the structure with the lowest fraction of (semi)metallic bonds, the highest content of homonuclear S-S bonds and the lowest Ge/S ratio. In such a film, the clustering of Er3+ ions, which is responsible for the intensity weakening, is suppressed. The film shows ≈990 nm upconversion photoluminescence originating from the Er3+: 4I11/2 → 4I15/2 transition under a 1550 nm excitation. The upconversion peak shape resembles that of the compositionally and structurally similar bulk glass.