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

A series of Tb/Eu-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 concentration. By doping only 0.15 mol% of Eu concentration, a comfortable warm white emission is promoted as a result of simultaneous emissions of Tb and Eu ions. A theoretical model is proposed to calculate the contributions of the emitted color of the donor (Tb) and acceptor (Eu) ions in terms of europium concentration. The energy transfer from Tb to Eu ions is corroborated by the luminescence spectra and decay time of Tb, with a maximum energy transfer efficiency of 76% for 28 mol% of Tb and 14 mol% of Eu. 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/Eu-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.