Near-infrared light excitation of h-BN ultra-wide bandgap semiconductor

We demonstrate a method to faithfully excite an ultra-wide bandgap semiconductor hexagonal boron nitride (h-BN) by using optical frequency upconversion technology. By means of Yb3+ and Tm3+ as dual bridging sensitizers, NaYF4:Yb3+, Tm3+, and Gd3+ microcrystals were excited by near-infrared light and generated high-energy (>6 eV) excited states. We fabricated a photoelectric conversion device by attaching the microcrystals to the surfaces of the h-BN thin film. When the device was irradiated with 980-nm near-infrared light, the Gd3+ ions in the microcrystals were populated to the high-energy excited states 5GJ through an internal 7-photon process, emitting 205 nm deep ultraviolet fluorescence and 195.3 nm vacuum ultraviolet fluorescence, which provided enough energy for h-BN photoexcitation. Dynamic analysis showed that Förster resonance energy transfer played a very important role in the optical excitation, and populating Gd3+ ions to high-energy excited states was the technical key.