Maximizing dopant photoluminescence in co-doped semiconductor nanoparticles for multiplex assays by tuning inter dopant electronic interactions: Synthetic co-doping or physical mixing of singly doped moieties?

Evaluation of inter dopant electronic interactions is important to maximize photoluminescence for their use as multiplex assays. This work compares the photophysical properties of lanthanide dopants in cases where the lanthanide moieties have been either synthetically co-doped in nanoparticles or two singly doped nanoparticles were physically mixed post-synthetically. Nd3+ − Sm3+ and Nd3+ − Er3+ were considered as dopants in the TiO2 nanoparticles. Remarkable differences in lanthanide emission have been observed between the two strategies of forming the multiple and distinct lanthanide containing assemblies. The inter lanthanide electronic interactions were found to be evident in the synthetic co-doping, with the same being absent in the physically mixed assembly. As a consequence, the Nd3+ emission in near infrared (NIR) and Sm3+, Er3+ emission in visible spectral range respectively have been found to be more pronounced in the physically mixed assembly as compared to that in the synthetically co-doped nanoparticles. The situation is however reversed for the Er3+ emission in NIR spectral range. These findings collectively provide a facile way to maximize dopant emission and indicate the importance of tuning the inter lanthanide electronic interactions for better suitability as multiplex agent, in an as-desired way.