Near-infrared-to-blue energy upconversion in LaF₃:Ho³⁺

Abstract

When the ⁵F₅ levels of Ho³⁺ in LaF₃ were resonantly excited with a red dye laser beam of 640 nm, blue and green emissions were detected from the ⁵G₅, the ⁵F₃, and the ⁵S₂(⁵F₄) levels at 416, 485, and 546 nm, respectively. We found that excited ions in the ⁵F₅ state undergo nonradiative relaxation to the ⁵I₆ state and are then upconverted to the 5Gs state by the absorption of a second photon, as well as by energy-transfer interaction. The upconversion efficiency into the ⁵F₃ state was estimated as ~1.1 × 10-4. We also observed energy-upconverted emissions from the ⁵F₃ and the ⁵F₃ levels when the material was excited with an 800-nm near-infrared laser. The absorption of a second laser photon from the ⁵I₆ state was found to be responsible for the upconverted green emission.