The series of Bi$^{3+}$ co-doped YPO$_{4}:Eu$^{3+}$ nanophosphors were successfully synthesized by the slow evaporation method. Bi$^{3+}$-doped and un-doped YPO$_4$:Eu$^{3+}$ phosphors were characterized by using powder X-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscopy. Photoluminescence (PL) properties and decay time of phosphors were studied at room temperature. The YPO$_4$:Eu$^{3+}$ and Bi$^{3+}$ exhibit enhancement in PL intensity and quenched at 0.5 mol% of Bi$^{3+}$ ions.

In this study, the spectral downshifting (DS) from ultraviolet (UV) light to near-infrared (NIR) radiation in Sr$_3$(VO$_4$)$_2$:Nd$^{3+}$ phosphor is reported. The prepared materials were characterized by X-ray powder diffraction(XRD) and photoluminescence (PL) properties along with steady state luminescence time decay curves were studied, which confirmed the energy transfer (ET) from VO$_4^{3−}$ ions to Nd$^{3+}$ ions. The DS phenomenon by phosphor was observed, which involved emission of NIR photons (1075 and 1064 nm) and visible photons (506 nm) from absorbed UV photons at 349 nm. The theoretical energy transfer efficiency (ETE) was calculated with the help of steady state luminescence time decay curves and the maximum ET efficiency approached up to 41.33%. The crystalline silicon (c-Si) cell has maximum efficiency in NIR region of solar spectrum due to an energy band gap of 1.12 eV.Sr$_3$(VO$_4$)$_2$:Nd$^{3+}$ can be potentially used as a NIR DC phosphor for c-Si solar cells.