Wide-range emission of Er3+/Yb3+ co-doped lanthanum niobates: A study of temperature and excitation-dependent luminescence aiming at applications in Biophotonics

We have synthesized Er³⁺,Yb³⁺ co-doped lanthanum niobate samples by a sol–gel route and investigated their luminescent properties under different excitation sources aiming at applications in Biophotonics. The samples were crystalline and composed primarily of orthorhombic La₃NbO₇ with secondary formation of monoclinic LaNbO₄. We verified NIR-to-visible upconversion with the naked eye under excitation at 980 and 1550 nm; emission in the green and red regions prevailed, respectively. X-ray excitation revealed prevalent emission in the blue region, attributed to the luminescence of NbO₄³⁻ groups in the lattice, as well as Er³⁺ emissions in the visible range. All the samples presented high relative thermal sensitivity (above 1.32 % K⁻¹) and repeatability above 97 % between 243 and 293 K. Based on the investigated luminescent properties, the samples prepared herein are versatile materials with a wide range of potential applications as scintillators, optical markers, energy converters for photodynamic therapy, and nanothermometers.