Structural and luminescence properties of Nd3+/Yb3+ codoped Al4B2O9 nanocrystalline powders

Morphological, structural and optical properties of Nd3+/Yb3+ codoped Al4B2O9 nanopowders prepared by the polymeric precursor method were investigated. The compounds previously heat-treated at 900 degrees C were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) techniques. The Al4B2O9 nanocrystals obtained possess an orthorhombic structure with grain dimensions between 10 and 20 nm. Photoluminescence (PL) spectra under excitation at 804 nm were collected and analyzed. The results indicate that the energy absorbed by Nd3+ (transition: I-4(9/2) -> F-4(5/2) + H-2(9/2)) is efficiently transferred to Yb3+ in samples having 2 mol% of Nd3+ and 1 mol% of Yb3+, increasing the emission from 930 nm to 1130 nm by 12.2 times in comparison with the samples doped with 1 mol% of Nd3+ and 1 mol% of Yb3+. The dynamics of the PL process was also investigated. The PL decay at 975 nm from Yb3+ (F-2(5/2) -> F-2(7/2)) and at 1080 nm from Nd3+ (F-4(3/2) -> I-4(11/2)) was studied. The Yb3+ F-2(5/2) level lifetime varies from 201 to 48 mu s while the lifetime of the Nd3+ F-4(3/2) level varies from 121 to 69 ms when the Nd3+ concentration is changed from 1 to 8 mol%. On the other hand, the Yb3+ F-2(5/2) lifetime varies from 176 to 15 mu s and the Nd3+ F-4(3/2) lifetime varies from 97 to 44 mu s when the Yb3+ concentration is changed from 1 to 8 mol%, due to interactions between the rare-earth ions. The present results show that Nd3+/Yb3+ codoped Al4B2O9 nanocrystalline powders have large potential to be tested in solar energy concentrators and IR laser devices.