cicCartuja Centro de Investigaciones Científicas de la cartuja
Título: Multi Photon Phosphors
Conferenciante: Dr. Andries Meijerink (Utrecht University)
Fecha: jueves, 24 de octubre de 2019
Horario: 11:00 h
Lugar: Salón de Grados
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, also known as phosphors, 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 not trivial but is needed to understand the mechanism and improve the efficiency of spectral conversion processes in multi-photon phosphors which is crucial for applications, including solar cells to reduce spectral mismatch losses.
In this presentation a short historical introduction to single- and 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 insight can be obtained in the mechanism and efficiency of up- and downconversion processes. An important aspect involves modelling of energy transfer and ligand quenching. For both up- and downconversion examples will be given on how modelling of luminescence decay curves can provide quantitative insight. A new ligand-quenching model will be presented and applied to understand multi-phonon vibrational quenching in NaYF4:Er,Yb upconversion nanocrystals. Finally 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 efficiency.
Illustration correlated photon counting to demonstrate two-photon emission using NaLaF4:Pr3+ as model system. (a) Two-photon emission on Pr3+. (b) Schematic set-up for correlated photon counting (c, d) Emission of Pr3+ in blue and red spectral region detected by separate detectors. (e) Correlated photon-counting signal.
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