Three-band white light from InGaN-based blue LED chip precoated with green/red phosphors

A three-band white light-emitting diode (LED) was fabricated using an InGaN-based blue LED chip that emits 460-nm blue light, and a green phosphor SrGa₂S₄: Eu²⁺ and a red phosphor Ca_1-xSr_xS: Eu²⁺ that emit 535-nm green and 615-nm red emissions, respectively, when excited by 460-nm blue light. When the white LED operated in a direct current (DC) 20 mA at room temperature, the Commission Internationale de l'Eclairage chromaticity coordinate (x, y), the color temperature Tc, and the color rendering index Ra are calculated to be (0.3236, 0.3242), 5937 K, and 92.2, respectively. The luminous efficacy of this white LED is about 15 lm/W at a DC 20 mA. With increasing DC from 5.0 to 60 mA, both the coordinates x and y of the white LED trend to increase, and consequently the Tc and the Ra increases and decreases, respectively.