Pristine and humidity-related photoluminescence in gadolinium niobate nanophosphors synthesized at low temperatures

•GdNb2O6,Gd1-xTmxNb2O6 compounds with an indirect band gap were synthesized for the first time via. hydrothermal method.•The various submicron morphologieswere obtained due to pH control of the precursor solution and without any surfactant.•The PL properties of GdNb2O6 and Gd1-xTmxNb2O6 varied between the morphologies before and after water elimination.•The GdNb2O6 presented a broadband PL emission between 400 and 700 nm, and Gd1-xTmxNb2O6 had a 457 nm blue emission.•Water on the surface of GdNb2O6 and Gd1-xTmxNb2O6 nanophosphorsinduced blue emission centered at about λem = 440 nm. In this work, gadolinium niobate nanophosphors were successfully synthesized and their pristine and humidity-related photoluminescence was studied. Polycrystalline layered bar-, cube-, and flower-like morphologies of this material were obtained without any surfactant in a controlled and reproducible manner. This gadolinium niobate compound was determined to be GdNb2O6 with an orthorhombic crystalline structure and a Pnma space group. Water adsorbed to the nanophosphors surface presented a 440 nm photoluminescence emission. This emission was a direct result of the excitation bands overlap of intrinsic GdNb2O6 matrix and water. Thulium-doped nanophosphors (Gd1-xTmxNb2O6) were also studied concerning Tm3+ and water-associated emissions. The GdNb2O6 and Gd1-xTmxNb2O6 compounds presented photoluminescence before and after low-temperature thermal treatment that varied between the morphologies. [Display omitted]