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

A series of LaNbO 4 :RE 3+ (RE = Tb and Eu) phosphors were successfully synthesized via a calcination-assisted hydrothermal reaction, where the vital roles of solution pH, calcination temperature and NbO 4 3− /La 3+ molar ratio in phase/morphology evolution of LaNbO 4 nanocrystals were elaborated. It was unambiguously demonstrated that monoclinic LaNbO 4 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. LaNbO 4 nanoparticles exhibit self-activated broad-band excitations ( 1 A 1 → 1 T 1,2 ) and emissions ( 3 T 2,1  →  1 A 1 ) within the NbO 4 3− ligand. Intriguingly, Tb 3+ /Eu 3+ incorporations allow for phase tailoring and full-visible-spectrum color-tunable luminescence, where the latter benefits from the effective NbO 4 3− → Tb 3+ → Eu 3+ energy transfer. LaNbO 4 :0.01 Tb 3+ ,0.01Eu 3+ 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.