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Two wavelength shifting (WLS) plastics with long emission
maxima are available.
Both are normally based on PVT but can alos be provided PVT
variants providing higher temperature characteristics.
WLS bars and discs absorb light at one wavelength and emit it
isotropically at longer wavelengths to provide useful mpdes
of light collection.
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The
green-emitting
EJ-280 is ideal for shifting the emission spectra of common
blue emitting scintillators.
The quantum efficiency of the fluorescent dopant in EJ-280 is
0.86, and its decay time under laser excitation is 8.5nSec.
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The
red emitting
EJ-284 is ideal for shifting green-emitting scintillators such
as CsI(Tl) into thered with a quantum efficiency near 95%.
There is, however, as indicated in the spectrum below, a useful
absorption maximum in the blue.
Its fluorescence decay time under laser excitation is 13nSec.
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The most common use for green WLS plastics is in the form of
long narrow bars air-coupled to blue scintillators arrayed
either in flat planes or in stacks.
The bars provide a compact means of light collection.
The green light is effectively turned 90° as a result of
the isotropic re-emission and transmitted by total internal
reflection to phototubes at both ends of the bar to achieve
a highly uniform light collection.
While there is a typical 75% loss of signal amplitude in these
systems, they can provide advantages over conventional light
collection methods.
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While there are standard formulas for these two WLS materials,
ELJEN Technology will respond to particular requirements to
make up custom formulations.
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