A promising blue-emitting phosphor CaYGaO4:Bi3+ for near-ultraviolet (NUV) pumped white LED application and the emission improvement by Li+ ions

Abstract

In this paper, a blue-emitting phosphor CaYGaO₄:Bi³⁺ is reported, which has a broad emission band peaked at 435 nm covering the 375 nm to 575 nm spectral region. The CIE coordinates of CaYGaO₄:Bi³⁺ is (0.1536, 0.0885) with color purity of 85.2%. Importantly, when Bi³⁺ ions are introduced into the CaYGaO₄ host, the excitation peak of Bi³⁺ is located at 370 nm, which matches well with the efficient near-ultraviolet (NUV) light emitting diode (LED) chips. Furthermore, the emission intensity of the CaYGaO₄:Bi³⁺ phosphor increased ∼1.47 times by adding Li₂CO₃ as a fluxing agent. The quantum efficiency of the prepared CaYGaO₄:Bi³⁺,Li⁺ phosphor reaches 45.7% under 370 nm excitation, and the PL intensity remains 76.3% of that at room temperature at 423 K. Using the CaYGaO₄:Bi³⁺,Li⁺ phosphor, coupled only with an orange phosphor (Sr,Ba)₃SiO₅:Eu²⁺ and a 370 nm NUV chip driven by 20 mA current, a NUV-based WLED, with chromaticity coordinates of (0.3610, 0.3360), correlated color temperature (CCT) = 4304 K and color rendering index (CRI) = 86.9, has been achieved. The white light emitting diodes employing CaYGaO₄:Bi³⁺ as a blue-emitting component exhibit superior electroluminescence properties. All results demonstrate that CaYGaO₄:Bi³⁺ is a promising blue component for application in NUV-based WLEDs.