Luminescence property improvement and controllable color regulation of a novel Bi3+ doped Ca2Ta2O7 green phosphor through charge compensation engineering and energy transfer

Abstract

In pursuit of warm WLEDs, exploration of novel phosphors and regulation of the existing phosphors are the two approaches usually used in the luminescent material field. In this work, we prepared green Ca₂Ta₂O₇:Bi³⁺ phosphors firstly and investigated their properties in detail. The as-prepared Ca₂Ta₂O₇:Bi³⁺ exhibits intense green emission in the 450-580 nm range under UV excitation, which matches well with the UV chip and can efficiently avoid the re-absorption problem. The improvement in the emission intensity and thermal stability of the phosphor was achieved using different charge compensation methods including codoping alkali metal ions (Li⁺, Na⁺, and K⁺), creating a cation vacancy, and host co-substitution (Ca²⁺ + Ta⁵⁺ → Bi³⁺ + Si⁴⁺, Ca²⁺ + Ta⁵⁺ → Bi³⁺ + Ge⁴⁺). Through systematic research, the emission intensity at room temperature was improved 2.1 times and the thermal stability was improved 2.9 times at 200 °C. By coating the prepared green sample with other commercial phosphors on the UV chip, warm WLEDs with Ra being 91.1 and CCT being 3990 K were obtained. Moreover, taking the Bi³⁺ → Eu³⁺ energy transfer strategy, the emitting color of the phosphor was tuned and yellow emitting phosphor was obtained. Our study indicates that Bi³⁺ doped Ca₂Ta₂O₇ might be a potential UV excited green phosphor for WLEDs. The charge compensation methods and the Bi³⁺ → Eu³⁺ energy transfer approach are valuable ways to improve and adjust the luminescence properties, which can further derivate a series of novel phosphors for improving the quality of WLED devices.