Multicolor and Warm White Emissions with a High Color Rendering Index in a Tb(3+)/Eu(3+)-Codoped Phosphor Ceramic Plate

A series of Tb(3+)/Eu(3+)-codoped phosphor ceramic plates with a high color rendering index (CRI) for a near-ultraviolet light emitting diode (LED) were fabricated. Color emission can be tuned from green to reddish as a function of Eu(3+) concentration. By doping only 0.15 mol% of Eu(3+) concentration, a comfortable warm white emission is promoted as a result of simultaneous emissions of Tb(3+) and Eu(3+) ions. A theoretical model is proposed to calculate the contributions of the emitted color of the donor (Tb(3+)) and acceptor (Eu(3+)) ions in terms of europium concentration. The energy transfer from Tb(3+) to Eu(3+) ions is corroborated by the luminescence spectra and decay time of Tb(3+), with a maximum energy transfer efficiency of 76% for 28 mol% of Tb(3+) and 14 mol% of Eu(3+). Warm white LEDs were constructed using a 380 nm UV chip and showed a CRI of 82.5, which was one of highest values reported for Tb(3+)/Eu(3+)-codoped samples. Color-correlated temperature (CCT), color coordinate (CC), and luminous efficacy (LE) were utilized to know the potentials as a phosphor converter in solid-state lighting.