A novel cyan-emitting phosphor KScSrSi2−yGeyO7:0.07Bi3+ for white LEDs with high color rendering index and low correlated color temperature

Abstract

To make up for the cyan gap (480–520 nm) in traditional tricolor (blue, green and red) phosphor-converted white light-emitting diodes (LEDs), it is highly important to find efficient cyan phosphors with broadband absorption in the near-ultraviolet range (370–420 nm) and bright emission at around 490 nm. Herein, a series of KScSrSi_2−yGe_yO₇:0.07Bi³⁺ phosphors with adjusted output color is reported, in which the Ge⁴⁺ ion was introduced as the inducing factor for controlling Bi³⁺ ion occupancy, and a new luminescence center was successfully induced at 370 nm. The variation in the related cell parameters and component contents confirmed the substitution of the Sc³⁺ sites with six coordination by the inducing ions and ruled out the possibility of defects, impurity, and matrix luminescence. Diffuse reflectance spectroscopy was used to explain the formation of new luminescence centers after the introduction of the inducing factor. The introduction of Ge⁴⁺ caused the spectral tuning of the phosphor from a blue-emitting band (λ_em = 455 nm) to a cyan-emitting band (λ_em = 490 nm), which enabled filling the cyan gap and realizing high-color-rendering white LEDs. A near-UV (λ_ex = 370 nm) pumped white LED fabricated using KScSrSi_1.5Ge_0.5O₇:0.07Bi³⁺ along with commercially available phosphors demonstrated a well-distributed warm white light with a high color-rendering index (Ra) of 92.3 and a low correlated color temperature (CCT) of 4339 K. Closing the cyan cavity with KScSrSi_1.5Ge_0.5O₇:0.07Bi³⁺ is ideal for generating a pleasant, full-spectrum warm white light.