Color tunable CaZnM(PO) (M = Lu/Tb, Lu/Eu, Tb/Eu) phosphors: luminescence, energy transfer and thermal stability studies for n-UV white LEDs.

A series of Tb- and Eu-doped CaZnLu(PO) (CZLP:Tb and CZLP:Eu) as well as CaZnTb(PO):Eu (CZTP:Eu) 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 or Eu 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 was fully substituted by the dopants, Tb or Eu, 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 and Eu) and their relative concentration. Furthermore, the energy transfer from Tb to Eu 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 and CaZnEu(PO) (CZEP), respectively. As a result, a white light emitting diode (WLED) device was fabricated using the optimal CZTP:0.2Eu yellow phosphor, the BaMgAlO:Eu (BAM:Eu) 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.