(La_0.97RE_0.01Yb_0.02)₂O₂S Nanophosphors Converted from Layered Hydroxyl Sulfate and Investigation of Upconversion Photoluminescence (RE=Ho, Er).

ABSTRACT: Phase-pure (La_0.97RE_0.01Yb_0.02)₂O₂S upconversion (UC) nanophosphors (average crystallite size ~?45 nm; RE=Ho, Er) were annealed from their hydrothermally crystallized layered hydroxyl sulfate precursors in flowing hydrogen at 1200 °C for 1 h, with water vapor as the only exhaust. Under 978-nm laser excitation (up to 2.0 W), the Ho³⁺-doped phosphor exhibited green (medium), red (weak), and near-infrared (strong) emissions at ~?546 (⁵F₄ ? ⁵I₈), 658 (⁵F₇ ? ⁵I₈), and 763 nm (⁵F₄ ? ⁵I₇), respectively, and has the stable chromaticity coordinates of about (0.30, 0.66) in the visible-light region (400-700 nm). The Er³⁺-doped UC phosphor, on the other hand, showed weak green (~?527/549 nm, ²H_11/2,⁴S_3/2 ? ⁴I_15/2), weak red (~668/672 nm, ⁴F_9/2 ? ⁴I_15/2), and strong near-infrared (~?807/58 nm, ⁴I_9/2 ? ⁴I_15/2) luminescence, whose emission color in the visible region drifted from yellowish-green [(0.36, 0.61)] to green [(0.32, 0.64)] with increasing excitation power. Analysis of the power-dependent UC luminescence found three- and two-photon processes for RE=Ho and Er, respectively, and the possible UC mechanisms were proposed.

SUBMITTER: Li JG 

PROVIDER: S-EPMC5570760 | biostudies-literature | 2017 Aug

REPOSITORIES: biostudies-literature