Modulation of Bi3+ luminescence from broadband green to broadband deep red in Lu2WO6 by Gd3+ doping and its applications in high color rendering index white LED and near-infrared LED

Abstract

Phosphors that exhibit tunable broadband emissions are highly desired in multi-functional LEDs, including pc-WLEDs and pc-NIR LEDs. In this work, broadband emissions were obtained and modulated in the unexpectedly wide spectral range of 517–609 nm for (Lu_0.99−xGd_xBi_0.01)₂WO₆ phosphors by tuning the Gd³⁺ content (x = 0–0.99). The effects of Gd³⁺ doping on phase constituents, particle morphology, crystal structure, and photoluminescence were systematically investigated. Broadband green emission was obtained from Gd³⁺-free (Lu_0.99Bi_0.01)₂WO₆ phosphors (x = 0), whose emission intensity was enhanced by 50% with 5 at% Gd³⁺ (x = 0.05). The phase transition happened when x > 0.50 and the broadband red-NIR emission was obtained when x = 0.75–0.99. Three luminescence centers were proved to be responsible for the broadband green emissions via crystal structure, spectral fitting and fluorescence decay analysis. A pc-WLED with a high color rendering index (R_a = 91.3), a stable emission color, and a low color temperature (3951 K) was fabricated from the (Lu_0.94Gd_0.05Bi_0.01)₂WO₆ broadband green phosphor, and an LED device that simultaneously emits high color rendering index white light and NIR light was obtained with the (Gd_0.99Bi_0.01)₂WO₆ broadband red-NIR phosphor. Night vision and noninvasive imaging were also demonstrated using the latter LED device.