Phase tailoring and color-tunable luminescence of LaNbO4:Tb3+,Eu3+ nanophosphors for deep UV-pumped pc-WLEDs application

A series of LaNbO4:RE3+ (RE = Tb and Eu) phosphors were successfully synthesized via a calcination-assisted hydrothermal reaction, where the vital roles of solution pH, calcination temperature and NbO43−/La3+ molar ratio in phase/morphology evolution of LaNbO4 nanocrystals were elaborated. It was unambiguously demonstrated that monoclinic LaNbO4 can be crystallized at solution pH = 8–13 after calcination at 900 °C. With pH = 10 precursor for example, higher calcination temperature led to phase transformation from orthorhombic to monoclinic structure. LaNbO4 nanoparticles exhibit self-activated broad-band excitations (1A1 → 1T1,2) and emissions (3T2,1 → 1A1) within the NbO43− ligand. Intriguingly, Tb3+/Eu3+ incorporations allow for phase tailoring and full-visible-spectrum color-tunable luminescence, where the latter benefits from the effective NbO43− → Tb3+ → Eu3+ energy transfer. LaNbO4:0.01 Tb3+,0.01Eu3+ phosphor exhibits stronger white-light emission, which gradually drifts to yellowish green at high heating temperature. This phosphor is an attractive candidate for optical thermometers and warm pc-WLED owning to excellent thermal stability, a low correlated color temperature of ∼5694 K and a high color rendering index of ∼90.