Photophysical Characterization of Er3+ doped and Er3+/Nd3+ co-doped Gd(OH)3 Nanocrystals: the Impact of Hexamethylenetetramine utilization for Morphology Engineering

Abstract

This work is a study on the photophysical properties of Er3+ doped and Er3+/ Nd3+ co-doped Gd(OH)3 nanocrystals. It also demonstrated up-conversion luminescence quenching arising from utilization of hexamethylenetetramine (HMTA) for the formation of rod-like morphologies. The synthesis was carried out via the precipitation technique. TG/DTA results show Gd(OH)3 phase is formed and stabilized in the temperature range of 30 to 106o C. Fourier Transform Infrared spectroscopy results indicate the presence of OH functional group, a signature of core OH- of the Gd(OH)3 host as well as the HMTA. X-ray diffraction measurement show hexagonal structure. The average crystallite sizes range between 23 and 35 nm in an increasing trend with increasing Nd3+ concentrations. SEM micrographs showed nanorods only for samples treated with HMTA. The 800 nm transition line was enhanced in the diffuse reflectance measurements with increasing Nd content, suggesting that upconversion emission may be enhanced as well. As Nd3+ ion concentrations increased, the valence band and conduction band edges also showed lateral changes towards more negative values. The Gd(OH)3:Er0.02 nanocrystals (without HMTA) produced the strongest upconversion emission at 560, 660, 758 and 875 nm. The emission at 875 nm had a 10-fold enhancement over the other emission bands. The pair of emissions, 758 and 875 nm, are employed in luminescence thermometry. Thus, the results from this work demonstrated that the synthesized nanocrystals have the potential to be applied in photonic related applications such as photodynamic therapy and luminescence thermometry. No upconversion emission was recorded for Er3+, Nd3+ co-doped Gd(OH)3 nanorods due to prevalence of OH-group from the HMTA used.