Host sensitized near infrared to visible photon upconversion in 1% Re4+ doped Cs2NaYbBr6

Cs2NaYbBr6 doped with 1% Re4+ was studied by optical absorption and luminescence spectroscopy. In the cubic host lattice the Re4+ ions substitute for the octahedrally coordinated Yb3+. Visible by eye red Re4+[T-2(2g)] upconversion (UC) luminescence centered around 14 000 cm(-1) is observed upon Yb3+[F-2(5/2)] near infrared (NIR) excitation around 10 805 cm(-1) between 10 and 300 K. An energy transfer (ET) step from Yb3+ [F-2(5/2)] to Re4+[E-2(g)/T-2(1g)] followed by an energy transfer upconversion (ETU) process on the Re4+ is shown to be the mechanism responsible for this phenomenon. For Yb3+ excitation at 10 805 cm(-1) with a power density of 1.3 kW/cm(2) the VIS/NIR emitted photon ratio is 5% at 10 K. (C) 2003 Elsevier B.V. All rights reserved.