Proceedings Article | 29 February 2008
KEYWORDS: Luminescence, Glasses, Silicon, Ceramics, Quantum efficiency, Matrices, Ultraviolet radiation, Absorption, Optical properties, Crystals
Fluorescence techniques are known for their high sensitivity and are widely used as analytical tools, detection methods
and imaging applications for product and process control, material sciences, environmental and bio-technical analysis,
molecular genetics, cell biology, medical diagnostics, and drug screening.
According to DIN/ISO 17025 certified standards are used for steady state fluorescence diagnostics, a method having the
drawback of giving relative values for fluorescence intensities only. Therefore reference materials for a quantitative
characterization have to be related directly to the materials under investigation. In order to evaluate these figures it is
necessary to calculate absolute numbers such as absorption/excitation cross sections and quantum yield. This has been
done for different types of dopands in different materials such as glass, glass ceramics, crystals or nano crystalline
material embedded in polymer matrices.
Samples doped with several fluophores of different emission wavelengths and decay times are required for fluorescent
multiplexing applications. Decay times shorter than 100 ns are of special interest. In addition, a proper knowledge is
necessary of quantum efficiency in highly scattering media. Recently, quantum efficiency in YAG:Ce glass ceramics has
been successfully investigated.
Glass and glass ceramics doped with threefold charged rare earth elements are available. However, these samples have
the disadvantage of emission decay times much longer than 1 microsecond, due to the excitation and emission of their
optical forbidden electronic transitions.
Therefore first attempts have been made to produce decay-time standards based on organic and inorganic fluophores.
Stable LUMOGEN RED pigments and YAG:Ce phosphors are diluted simultaneously in silicone matrices using a wide
range of concentrations between 0.0001 and 2 wt%. Organic LUMOGEN RED has decay times in the lower nanosecond
range with a slight dependency on concentration and temperature. In addition, the well-known decay properties of
inorganic YAG:Ce are observed also embedded in silicone matrix. Luminescent silicone layers are obtained with
thicknesses between 150 and 300 µm and no change of decay time, which has been determined to be between 60 and 62
ns.
Finally, first results are shown for fluorescent CaF2:Pb glass ceramics embedded in a silicate glass matrix. Wavelength
accuracy and lifetime are characterized for different environmental conditions such as temperature treatment and UV
irradiation.
Moreover, intensity patterns, e.g. line profiles and results, are discussed on homogeneity and photo and thermal stability,
respectively. Fluorescence (steady state, decay time) and absorption (remission, absorption) spectroscopy are employed
as diagnostic methods to get a microscopic view of the relevant physical processes.
The work is funded by BMBF under project number 13N8849.
