Optical Spectroscopy III
Er3+:YLiF4 Emission Spectrum and Up-conversion
In the following exercises students will excite Er3+
with a diode laser and obtain emission spectra. From the spectra, they will
identify energy levels important in the visible emission of trivalent erbium.
Among the observed emission lines, several are due to up-conversion. Students
identify these emission lines and the excitation pathways, which enable this
Inexpensive compact semiconductor diode lasers are readily
available, which supply high intensities of near infrared light. A common
technological problem is that semiconductors seldom emit in the visible region
of the spectrum. One solution to this problem is the use of an up-converting
material. That is, a material which absorbs photons of a certain energy and
emits photons with higher energy. The details of this process will be made
apparent in the following exercise.
following procedure will guide you through the measurement of the emission of
Erbium in a crystal host, the identification of energy levels, and the analysis
of linear and nonlinear absorption processes.
by running the Ocean Optics S2000 control software. Make sure the correct
spectrometer is installed and set the acquisition parameters.
on the ILX Lightwave LDX-3525 current source and set the diode current to
50 mA. Place a white card in the
beam so that the spectrometer detects some of the scattered laser light. Note the spectral width and wavelength
of the laser. Is the laser
narrower in line width than the spectrometer resolution?
CAUTION: THE DIODE LASER
EMITS INTENSE RADIATION AND EXPOSURE TO THE EYES AND SKIN MUST BE AVOIDED. PAY
PARTICULAR ATTENTION TO REFLECTIONS OF THE LASER BEAM, AS THESE ARE SOMETIMES
DIFFICULT TO PREDICT.
the Er3+:YLiF4 crystal in the cuvette holder such
that the diode laser is focused into the crystal and the emitted light is
observed through the spectrometer.
the emission spectrum of the sample. Notice whether there is any emission
of photons with energies greater than those used to excite the
sample. Your report should have a
graph of the emission spectrum. Identify and label the
transitions on the graph.
the peak intensity of one line originating from each of the J-levels. For
peaks at higher energy than the excitation energy, measure the peaks of
all lines. Repeat the measurement with the OD filters and
combinations of the OD filters (.15, .30, .60). Plot the peak intensity emitted from each level as a
function of the excitation intensity.
Be sure that if you change the integration time, you account for
this in your data.
differences are there between the emissions from the various levels? Use
your data and the Er3+ energy level diagram to explain the
mechanism behind the up-converted emission. It is a multi-level
process but any explanation in which energy is not conserved will be
Suggested reading (a step ahead): A new
process, called quantum cutting, which can be considered the opposite of
up-conversion is now being studied. Future mercury-free fluorescent lighting
will likely be produced using this process.