398
P. Singh et al.
and thus the excitation energy is relocated to killer sites from lattice. These killer
sites may be impurities or crystal defects, etc. Cross-relaxation between the activators ions is also responsible for the concentration quenching above certain critical
value of the concentration of the activator.
2 Experimental Setup for Photon Upconversion
Spectroscopy
In a distinctive fluorescence measurement setup, the main components are excitation source, monochromator and detector. Light from an excitation source is passed
through the monochromator and then a wavelength of choice is focused on the sample.
The fluorescence emitted by the sample is focused on a second monochromator and
then passes to a detector. The detector is usually placed at 90° to the incident light
beam to avoid the noise (due to radiant power fluctuations) in fluorescence detection.
This arrangement also minimizes the risk of damage of detector through transmitted
and reflected incident beam. In traditional fluorescence spectrometer, xenon lamp is
generally used as an excitation source which has a broad emission spectrum from
250 to 1000 nm. The most widespread monochromators, based on blazed diffraction grating, are used at excitation and emission positions. In case of UC emission
measurement setup, the excitation source is a NIR laser. Therefore, it avoids the use
of excitation monochromator.
Figure 5 represents a typical schematic for laser excitation based UC emission
measurement setup. A laser beam is focused on the sample with suitable optical
arrangement of lens. The UC fluorescence emitted by the sample is focused on a
monochromator and then passes to a detector. In our measurement, UC emission
spectra are recorded using a photomultiplier tube (PMT) attached with a monochromatror (model: iHR320, Horiba Jobin Yvon). A diode laser excitation (980 nm,
continuous mode, 2 W, power tunable) is used for NIR to visible upconversion. This
setup can be used for kinetics measurement also. A normal fluorescence spectrometer can also be used for UC emission measurement provided a separate laser is
used from outside for excitation purpose. In this case, excitation line from xenon
lamp shall be blocked. Further, UC based decay measurements are performed by
chopping the 980 nm laser line through a mechanical chopper. The PMT output
of a monochromator (Spex, Coherent) is interfaced with an oscilloscope (analog to
digital scope-HM1507). The decay data and curve observed through oscilloscope
are readout using software SP107.
P. Singh et al.
and thus the excitation energy is relocated to killer sites from lattice. These killer
sites may be impurities or crystal defects, etc. Cross-relaxation between the activators ions is also responsible for the concentration quenching above certain critical
value of the concentration of the activator.
2 Experimental Setup for Photon Upconversion
Spectroscopy
In a distinctive fluorescence measurement setup, the main components are excitation source, monochromator and detector. Light from an excitation source is passed
through the monochromator and then a wavelength of choice is focused on the sample.
The fluorescence emitted by the sample is focused on a second monochromator and
then passes to a detector. The detector is usually placed at 90° to the incident light
beam to avoid the noise (due to radiant power fluctuations) in fluorescence detection.
This arrangement also minimizes the risk of damage of detector through transmitted
and reflected incident beam. In traditional fluorescence spectrometer, xenon lamp is
generally used as an excitation source which has a broad emission spectrum from
250 to 1000 nm. The most widespread monochromators, based on blazed diffraction grating, are used at excitation and emission positions. In case of UC emission
measurement setup, the excitation source is a NIR laser. Therefore, it avoids the use
of excitation monochromator.
Figure 5 represents a typical schematic for laser excitation based UC emission
measurement setup. A laser beam is focused on the sample with suitable optical
arrangement of lens. The UC fluorescence emitted by the sample is focused on a
monochromator and then passes to a detector. In our measurement, UC emission
spectra are recorded using a photomultiplier tube (PMT) attached with a monochromatror (model: iHR320, Horiba Jobin Yvon). A diode laser excitation (980 nm,
continuous mode, 2 W, power tunable) is used for NIR to visible upconversion. This
setup can be used for kinetics measurement also. A normal fluorescence spectrometer can also be used for UC emission measurement provided a separate laser is
used from outside for excitation purpose. In this case, excitation line from xenon
lamp shall be blocked. Further, UC based decay measurements are performed by
chopping the 980 nm laser line through a mechanical chopper. The PMT output
of a monochromator (Spex, Coherent) is interfaced with an oscilloscope (analog to
digital scope-HM1507). The decay data and curve observed through oscilloscope
are readout using software SP107.