Enhanced green upconversion luminescence in Yb–Tb co-doped sintered silica nanoporous glass Yingbo Chu • Yu Yang • Zijun Liu • Lei Liao • Yibo Wang • Jiaming Li • Haiqing Li • Jinggang Peng • Nengli Dai • Jinyan Li • Luyun Yang Received: 3 September 2014 / Accepted: 16 November 2014 / Published online: 27 November 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract We report on a new kind of green-emitting (543 nm) high-silica luminous glass, which is fabricated by sintering of Yb 3? –Tb 3? co-doped nanoporous glass. The fluorescence spectra show that there is an energy transfer between Yb 3? and Tb 3? . The energy transfer process can be enhanced by addition of Al 3? into the Yb 3? –Tb 3? co- doped nanoporous glass, and the energy transfer rate can be enhanced more than three times than that of Yb 3? –Tb 3? co-doped porous glass. The role of Al 3? has been dis- cussed, and the fluorescence decay curve reveals that the Al 3? play an important role in the energy transfer process. 1 Introduction Nowadays, compact fiber lasers and amplifiers operating in the visible range have been paid considerable attention because of their numerous applications in optical data storage, biomedical, laser processing and so on [1–3]. The green-emitting from 5 D 4 energy level of Tb 3? has some merits such as higher color purity, lower loss in seawater and higher luminescence intensity. Therefore, the spectro- scopic properties of Tb 3? doped materials have been exhaustively investigated for purchasing high-efficient green lasers [1, 2]. However, when the 5 D 4 energy level of Tb 3? was excited at 488 nm, it was found that the excited- state absorption (ESA) caused by absorption from 5 D 4 level suppresses the signal gain seriously [4]. In addition, the ESA is also the possible reason of a photodarkening effect in Tb 3? -doped silicate fibers [4, 5]. Upconversion lumi- nescence (UCL) in rare-earth (RE)-doped materials can be an efficient mechanism to overcome the above problems and obtain visible (VIS) and near-infrared (NIR) laser [6– 8]. Usually, there are two kinds of rare-earth ions in UCL materials: one kind of ions act as donor, and another kind of ions act as acceptor; upon pumping with lower-energy photons, the donors will be excited to excited states, and then they will transfer their absorbed energy to acceptors by energy transfer mechanisms [9]. Currently, there are several common upconversion mechanisms such as exci- ted-state absorption, energy migration, cooperative up- conversion, photon avalanches[18]. It is noticed that the mechanism of cooperative upconversion is an effective process that the donor can simultaneously transfer their absorbed energy of photons to the acceptor which has no energy level near the position of the excited level of the donor. In this special energy transfer mechanism, Yb 3? usually acts as a donor because of the simpler two-level structure and larger absorption cross section. The scheme of co-doping of Yb 3? –Tb 3? is promising to realize green- emitting laser. In Yb 3? –Tb 3? co-doped materials, two excited Yb 3? (sensitizer) ions simultaneously transfer their energy to one Tb 3? (activator) ion, and the Tb 3? is excited to the 5 D 4 level. Plenty of UCL materials doped with Yb 3? –Tb 3? were reported up to now, but most of them are limited in non- silica glass systems such as silicate, fluoride, borate and phosphate glasses. Although these glasses can be heavily doped with rare-earth ions without apparent concentration quenching, the intrinsic drawbacks of these materials such as poor mechanical strength, poor heat resistance, difficult to couple with conventional silica optical fiber limit their applications. So far, appropriate host matrix for 543-nm Y. Chu  Y. Yang  Z. Liu  L. Liao  Y. Wang  J. Li  H. Li  J. Peng  N. Dai  J. Li  L. Yang (&) Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China e-mail: luyunyang@gmail.com 123 Appl. Phys. A (2015) 118:1429–1435 DOI 10.1007/s00339-014-8903-4