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.
Diode Laser Operation and Characteristics
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.
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.
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
94 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?
- Zoom in on the laser peak. Turn on the Temperature Controller and set the resistance to 3.6kohms. Watch the laser wavelength change in the OO software. As the resistance increases, the temperature of the laser is getting colder. Does the direction of the wavelength shift make sense? Measure the wavelength of the laser once the temperature has stabilized (R=3.6kohms).
Er3+:YLiF4 Emission Spectrum
the Er3+:YLiF4 crystal so
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 three lines that are below and three lines that are above the laser energy. Since the laser is exciting levels within the 4F9/2 manifold of states, choose one level that is above and one that is below the laser energy. The other four levels should come from different manifolds. Repeat the measurement with the OD filters and
combinations of the OD filters (0.15, 0.30, 0.60).
Be sure that if you change the integration time, you account for
this in your data. Plot the log of the peak intensity emitted from each level as a
function of the log of the excitation intensity. Because upconversion is a two-step process, the intensity dependence (or "power dependence") should be different than that of normal emission. Does your data confirm this? What is the power dependence for the lines?
- Use the power dependence you've just found and your solution to problem 3 from Chapter 9 to predict how much stronger the upconversion intensity would be if the crystal was cooled to 4.2K. Assume that all initial transitions are made from the 0cm-1energy state.
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
- Draw a block diagram of the experimental setup.
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.