Color tunable Ca 8 ZnM(PO 4 ) 7 (M = Lu/Tb, Lu/Eu, Tb/Eu) phosphors: luminescence, energy transfer and thermal stability studies for n-UV white LEDs

A series of Tb 3+ - and Eu 3+ -doped Ca 8 ZnLu(PO 4 ) 7 (CZLP:Tb 3+ and CZLP:Eu 3+ ) as well as Ca 8 ZnTb(PO 4 ) 7 :Eu 3+ (CZTP:Eu 3+ ) phosphors have been prepared via the traditional high-temperature solid-state reaction. X-ray powder diffraction (XRD) patterns of the as-prepared phosphors indicate that the introduction of Tb 3+ or Eu 3+ affects neither the phase impurity nor the crystal structure of the CZLP host lattice. The concentration dependent photoluminescence (PL) spectra reveal that even if Lu 3+ was fully substituted by the dopants, Tb 3+ or Eu 3+ , the phenomenon of concentration quenching would not occur. Color tunable emissions from green to red can be realized by adjusting the type of doping ion (Tb 3+ and Eu 3+ ) and their relative concentration. Furthermore, the energy transfer from Tb 3+ to Eu 3+ was confirmed and the mechanism was determined to be the dipole–quadrupole interaction. In addition, the quantum efficiencies were found to be 0.61, 0.58 and 0.85 for CZTP, CZTP:0.2Eu 3+ and CaZnEu(PO 4 ) 7 (CZEP), respectively. As a result, a white light emitting diode (WLED) device was fabricated using the optimal CZTP:0.2Eu 3+ yellow phosphor, the BaMgAl 10 O 17 :Eu 2+ (BAM:Eu 2+ ) blue phosphor and a 370 nm near-ultraviolet (n-UV) chip. The obtained device displays a suitable color rendering index (CRI, ∼81.3) and correlated color temperature (CCT, ∼2634 K) value, indicating its potential application in n-UV LEDs.