Research

Introduction

The research of the LumiLab team is mainly focused on inorganic luminescent materials (also known as phosphors), and studies the relation between the structural, electronic and optical characteristics of these materials. These phosphors generally consist of an insulating host compound – oxides, sulfides, nitrides, … -  doped with luminescent ions. The dopants are most often rare earth elements; while the optical transitions in most rare earth elements are 4f-4f transitions, showing sharp excitation and emission features with low absorption strength, both Ce3+ and Eu2+ are rare earth ions offering broad excitation and emission bands that are highly tunable over the entire visible range. These properties make the latter ions omnipresent in white LEDs for lighting, where phosphors convert part of the light of a blue LED to green and red, ultimately leading to a broad spectrum mimicking natural white light [1].  Due to the high cost and limited supply of rare earths, alternative dopants such as transition metals (Cr3+, Mn4+) and so-called s2-ions (Pb2+, Bi3+) are also explored. These alternative ions are also applied when emission in the near-infrared is needed, e.g. for applications in biological imaging.

Next to applications in lighting, phosphors are investigated showing mechanoluminescence (ML, useful for pressure sensing [2]) and persistent luminescence ('glow-in-the-dark' materials for safety applications [3,  4]). Finally, LumiLab is active in a number of other projects on optically active ‘smart’ materials, such as Sm-chalcogenides as pressure-sensitive phase changing materials [5] and photocatalytically active compounds for air purification.

Over the years LumiLab has acquired an extensive set of analytical techniques for studying phosphors. This includes high performance UV-Vis-NIR spectrophotometry, photoluminescence excitation, emission and decay spectroscopy, electron microscopy, cathodoluminescence and thermoluminescence spectroscopy [6, 7, 8, 9]. While the research is mostly based on experiments and phosphor materials that are synthesized in-house, energy level and device modeling are developed to interpret the measurement data [10, 11, 12].

In addition to several research collaborations, the LumiLab team at Ghent University regularly receives visitors from all over the world. LumiLab remains open to all kinds of new formal or informal collaborations in the future. 

 

Publications

More publications

Facilities

Perkin Elmer multifunctional spectrophotometers

 Two Perkin Elmer Lambda 1050 UV-Vis-NIR spectrophotometers for both specular and diffuse transmission and reflection measurements. One of the instruments is dedicated to diffuse transmission and reflection measurements, using an integrating sphere or praying mantis. Using the latter attachment, measurements can be performed under a controller atmosphere and at elevated temperature. The other instrument is equipped with a TAMS (total absolute measurement system) and can be used for angle dependent transmission and reflection measurements under controlled polarization conditions, including measurement of BRDF (bidirectional reflection distribution function) and mapping of wafer surfaces.

 perkin&elmer

 

Intensified CCD

This instrument is used for measuring integrated and time-resolved optical emission spectra (both electro- and photoluminescence). On periodic signals, a time resolution down to 2 ns can be obtained. It is coupled to a 0.5 m Ebert monochomator. For photoluminescence decay measurements, a 337 nm pulsed nitrogen laser is available (pulse length < 1ns). Using the dye extension, the excitation can be tuned between 360 and 600nm.

Type: Andor DH720

Andor DH720

Ball mill

Planetary ball mill for powerful and quick grinding of material with feed size < 10 mm resulting in a final fineness < 1 µm, or for colloidal grinding < 0.1 µm. This benchtop model consists of 1 grinding station equipped with a ZrO2 grinding jar (50 ml). Both dry and wet grinding are possible.

Type: Retsch PM 100

Ball Mill

UV-VIS-NIR spectrophotometer

Double beam – double monochromator UV-VIS-NIR spectrophotometer for the optical characterisation of thin films. Measurement range from 200 to 3300nm. An extension is available to measure the (diffuse) reflectance of powders and thin films (200 - 2000nm), using an integrating sphere.

Type: Varian Cary 500

 Varian Cary 500

Climate chamber

With this device accelerated aging can be tested at a combination of high temperature and humidity.

Type: Memmert HCP 108

Climate Chamber

 

Fluorescence spectrometer

Photoluminescence setup, enabling high resolution excitation and emission measurements. The combination of a Xe arc lamp and a double excitation monochromator allows selecting an excitation in the range from 250 to 900nm, with narrow band width and low stray light. At the emission side, two detectors are available for measurements between 300 and 1650nm. The setup can be extended with a cryostat, for measurements between 4 and 500K.

Type: Edinburgh FS920

Edinburgh FS920

 

Infrared camera

This accurate non-contact temperature sensors offers comprehensive visual temperature monitoring of our experiments.

Type: FLIR A35

FLIR InfraRed Camera

 

Glovebox

The glovebox working station offers an oxygen-free atmosphere to store and prepare samples.

Type: MBRAUN LABstar

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Portable spectrometers

Two portable, USB powered, CCD-based spectrometers. One is optimized for measurements in the 200-950nm range with high sensitivity (QE65000), one is optimized for high resolution in the visible range (HR2000+).

Type: Ocean Optics QE65000 and HR2000+

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Scanning electron microscope

Fully automated VP-SEM equipped with a number of extensions for chemical and structural analysis. These features include EDX (energy dispersive x-ray analysis), CL (cathodoluminescence) and a cooling/heating stage.

Type: Hitachi S-3400N

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TL/TQ setup

Homemade setup for thermoluminescence spectroscopy with low energy photon excitation.

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