Abstract
A series of Tb3+/Eu3+-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 Eu3+ concentration. By doping only 0.15 mol% of Eu3+ concentration, a comfortable warm white emission is promoted as a result of simultaneous emissions of Tb3+ and Eu3+ ions. A theoretical model is proposed to calculate the contributions of the emitted color of the donor (Tb3+) and acceptor (Eu3+) ions in terms of europium concentration. The energy transfer from Tb3+ to Eu3+ ions is corroborated by the luminescence spectra and decay time of Tb3+, with a maximum energy transfer efficiency of 76% for 28 mol% of Tb3+ and 14 mol% of Eu3+. 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 Tb3+/Eu3+-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.
Highlights
In the last decade, phosphor-converted light emitting diodes have been introduced into the market to conquer the deficiencies of fluorescent and incandescent lamps
Current phosphor-converted light emitting diodes (pcLEDs) are basically a mixture of a phosphor converter and a silicon binder placed in the top of a blue light emitting diode (LED) chip (InGaN), and the combination of both colors yields white light
Luminescence glasses, glass ceramics, phosphor in glass, and ceramic phosphor plates have emerged as good candidates to replace the silicon binder in high-power LEDs [2,3,4,5]
Summary
Phosphor-converted light emitting diodes (pcLEDs) have been introduced into the market to conquer the deficiencies of fluorescent and incandescent lamps. Luminescence glasses, glass ceramics, phosphor in glass, and ceramic phosphor plates have emerged as good candidates to replace the silicon binder in high-power LEDs [2,3,4,5] Among these approaches, special attention has concentrated on ceramic phosphor plates because of their superior thermal stability over different approaches for solid-state lighting [6]. The last property is key for the development of stable high-power LEDs and can be controlled through network formers, network modifiers, and network intermediators [7,8] Even though this system shows attractive thermal and optical properties, most of the high-power systems using one single phosphor do not meet the characteristics for satisfactory color rendering index (CRI) and low color-correlated temperature (CCT) for residential lighting applications [9,10]. A second phosphor to compensate the weak red emission of YAG:Ce3+
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