(Lecture, Jul 25) Multi-photon phosphors
2017-07-21 readCount:311
Title: Multi-photon phosphors
Speaker: Prof. Andries Meijerink (Royal Netherlands Academy of Arts and Sciences, Utrecht University)
Venue: Room 402, State Key Laboratory Of Luminescent Materials And Devices, Wushan Campus
Time: Tuesday, Jul 25, 2017, 16:00
Lanthanides have transformed the world of lighting in the past 40 years. Presently, almost all artificial light sources rely on emission of light by lanthanide ions. In many luminescent materials, one-to-one photon conversion downshifts one high energy photon to one lower energy photon in the desired spectral region. However, recently, there is a significant increase of attention for multi-photon phosphors relying on multi-photon conversion processes, either upconversion or downconversion. Insight in the multi-photon processes is needed to understand the mechanism and improve the efficiency of multi-photon phosphors.In this presentation a short historical introduction to multi-photon conversion phosphors will be followed by an overview of recent developments of efficient up- and downconversion materials. Next it will be discussed how the insight can be obtained in the mechanism and efficiency of up- and downconversion processes1,2. An important aspect involves modelling of energy transfer using microscopic models based on actual distributions of lanthanide ions. These models take into account the distributions of donor-acceptor distances imposed by the crystal structure of the host material. As an illustrative example, energy transfer from Ce3+ to Yb3+ will be discussed. A second example involves up-and downconversion in oxysulfides. Efficient up- and downconversion can be realized in this class of materials, including a record high 12% upconversion quantum yield and a one-to-four downconversion process in Tm3+ doped oxysulfides. A new method will be presented that provides direct proof for downconversion. Correlated emission of photons in photon cutting materials can serve as a fingerprint for the occurrence of downconversion and can even be used to quantify the downconversion efficiency3.Many new applications of up- and downconversion materials require nanoparticles e.g. in spectral conversion for solar cells and nanothermometry. Up- and downconverting nanoparticles suffer from stronger quenching and reduced thermal stability in comparison to their bulk analogues. Here we will give insight in the quenching mechanism in upconversion nanoparticles. Highly stable and efficient upconversion nanoparticles for nanothermometry are reported which operate at temperatures exceeding 900 K and potential applications are discussed4. Finally an outlook is provided on the future of multi-photon phosphors and nanophosphors.
1. Modeling the Cooperative Energy Transfer Dynamics of Quantum Cutting for Solar Cells, F. T. Rabouw and A. Meijerink, The Journal of Physical Chemistry C 119, 2364-2370 (2015).
2. Upconversion Dynamics in Er3+-Doped Gd2O2S: Influence of Excitation Power, Er3+ Concentration, and Defects, R. Martín-Rodríguez, F. Rabouw, M. Trevisani, M. Bettinelli and A. Meijerink, Advanced Optical Materials 3, 558–567 (2015).
3. Non-poissonian statistics from macroscopic photon cutting materials, M. de Jong, A. Meijerink and F.T. Rabouw, Nature Comm., 8, 15537 (2017).
4. NaYF4:Er3+, Yb3+ core/shell upconversting nanocrystals for luminescence thermometry up to 900 K, R.G. Geitenbeek, P.T. Prins, W. Albrecht, A. van Blaaderen, B.M. Weckhuysen, A. Meijerink, J. Phys. Chem. C 121, 3502-3510 (2017).
Andries Meijerink received his MSc and PhD degree in Chemistry at Utrecht University. After a post-doc in Madison (University of Wisconsin) he returned to Utrecht in 1991. In 1996, at the age of 32, he was appointed at the chair of Solid State Chemistry in the Debye Institute of Utrecht University where he leads an active group in the field of luminescence spectroscopy of quantum dots and lanthanide ions.In the field of lanthanide ions his work involves fundamental research on the energy level structure of both 4fn and 4fn-15d states and finding new concepts related to applications in solar cells, LEDs and scintillators. His research on quantum dots is aimed at unraveling the influence of quantum confinement and surface effects on the electronic structure and exciton dynamics of quantum dots through optical spectroscopy and using the quantum dots as labels in bio-imaging. Research on luminescence of doped nanocrystals integrates the two themes. Recent work has resulted in a better fundamental understanding of photonic effects on optical processes, insight in energy transfer processes and application of luminescent nanocrystals as probes. The work has resulted in over 350 publications and 10 patents and is highly cited. For his research Andries Meijerink received several awards, including the Shell Incentive Award (1995), the Gold Medal of the Royal Dutch Chemical Society (1999) and the Centennial Award for Luminescence and Display Materials from the Electrochemical Society (2002). In 2009 he was elected into the Royal Dutch Academy of Sciences.

Announced by School of Materials Science and Engineering