Characterization and growth of doped-PbS in situ with Bi3+, Cd2+ and Er3+ ions by chemical bath

The growth of PbS nanocrystals doped in situ simultaneously with Er3+-Cd2+-Bi3+ solutions at different proportions was examined with the aim of investigating the morphological, optical and structural changes of the nanocrystals obtained. A brief summary of the chemical equilibria plus the Gibbs free energy changes are presented. Fourier transform infrared spectroscopy (FTIR) spectra showed an absorption band located at similar to 3356 cm(-1) attributed to stretching of -OH groups and a sharp stretching band at similar to 1932 cm(-1) assigned to vibration mode of CO32- ions. This absorption bands are generally due to the decomposition of thiourea in alkaline medium. X-ray diffraction (XRD) patterns exhibited a cubic phase in all films and the grain size (GS) of the undoped samples was similar to 6.57 nm, whereas for doped films was similar to 6.40-4.16 nm. Transmission Electron Microscopy (TEM) confirmed the structural characteristics of the nanocrystals. Absorbance spectra of PbS films exhibited five absorption bands located at similar to 346, similar to 585, similar to 615, similar to 670 and similar to 775 nm due to strong confinement effect. This multiplex of bands presented in PbS is induced by the simultaneous incorporation of the ions. The shift of the band gap energy is associated with the decrease of crystalline size in PbS films. On the other hand, a small absorption band located at similar to 446 nm, corresponding to (4)(F7/2) -> (4)(I5/2) (4f ->. 4f transitions of Er3+ ions) was also observed. A small blue emission band centered at similar to 446 nm was originated from the allowed P-3(1) -> S-1(0) transition of Bi3+ ions. Band gap energy of nanocrystals showed a shift in the similar to 1.4-2.6 eV range. The structural experimental results are associated with the optical changes confirming the gradual incorporation of the dopant ions in the crystallites network. Raman spectra showed two bands located at similar to 450 cm(-1) due to the first overtone of the LO phonon (2LO) and other band located at similar to 200 cm(-1) which has been attributed to the LO (G) phonon, confirming the existence of doped-PbS nanocrystals.