Bright Persistent Green Emitting Water-Dispersible Zn2GeO4:Mn Nanorods
Luminescent materials with bright and persistent emission have been fetching significant attention among scientific community owing to their tremendous potential in the area of bioimaging, solid state lighting, and security applications. Moreover, when they are in nanodomain and water dispersible, it further improves their potentials for in vivo and in vitro imaging. With this intention, we have synthesized water dispersible nanorods (NRs) of Zn2GeO4 (ZGO) and Mn2+-doped Zn2GeO4 (ZGOM) using the hydrothermal method. For the ZGOM NRs, we have also optimized the dopant Mn2+ concentration, pH value of the reaction medium, and the precursor Zn/Ge molar ratio. The ZGO NRs emit bright bluish white (cool-white) emission under UV irradiation which is ascribed to various kinds of defects present in the NRs. On the other hand, the ZGOM NRs display highly bright green luminescence under UV irradiation with quantum yield (QY) of 52%. The best emission output was observed with dopant concentration of 2.0mol% Mn2+, pH of 10.5, and Zn:Ge = 1:2. This fact suggests that zinc deficiency and excess of germanium leads to enhancement in emission intensity. More importantly, the undoped ZGO NRs could not display any kind of persistence luminescence whereas the ZGOM NRs show excellent green afterglow properties (even visible with naked eye) on irradiation with 254 nm UV light. Such water dispersible nanocrystals with high QY and afterglow properties offer the prospect of cost-effective and environmentally benign phosphors for multifunctional applications in society.