New insight into rare-earth doped gadolinium molybdate nanophosphor assisted broad spectral converters from UV to NIR for silicon solar cells

We have successfully synthesized rare-earth doped gadolinium molybdate Gd-2(MoO4)(3):Re3+ (Re3+ - Eu3+, Tb3+, Tm3+ and Er3+/Yb3+) nanophosphors for solar cell application as a broad spectral converter from the ultraviolet (UV) to the near infrared (NIR) regions in a single host lattice using a facile solid state reaction method. The gross structure, surface morphology and microstructure of these nanophosphors have been investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission/high-resolution transmission electron microscopy (TEM/HRTEM) techniques, respectively. Photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopic methods have been used to explore the striking luminescence properties of the synthesized nanophosphors. The Gd-2(MoO4)(3):Eu3+ nanophosphor exhibits a hypersensitive red emission (616 nm) at an excitation wavelength in the range of 250-475 nm corresponding to a D-5(0)-F-7(2) transition. The Gd-2(MoO4)(3):Tb3+ and Gd-2(MoO4)(3):Tm3+ nanophosphors demonstrate a strong green emission at 541 nm and a deep blue emission at 453 nm upon an excitation wavelength of 378 nm and 266 nm, respectively. Moreover, the upconversion characteristic of the Gd-2(MoO4)(3):Er3+/Yb3+ nanophosphor exhibits strong green emission at 545 nm and red emission at 657 nm corresponding to S-4(3/2)-I-4(15/2) and F-4(9/2)-I-4(15/2) transitions respectively. Furthermore, the Gd-2(MoO4)(3):Er3+/Yb3+ upconversion nanophosphor emits in the NIR spectrum region at 994 nm upon a 980 nm excitation wavelength. Hence, the obtained PL emission results with a lifetime in milliseconds reveal that these nanophosphors could be futuristic promising broad spectral converter phosphors which may possibly integrate with the next-generation Si-solar cell to enhance the efficiency of the cell