pallab said:
Project: spectroscopic studies on Eu3+/Yb3+ doped Y2O3 phosphors
Yes, I am clueless but I am trying to fathom out the physics behind this luminescence.
what I was considering as true for this luminescence, faced a challenge to the result of UV light excitation
Y
2O
3. I see, so you are working on one of the most common lanthanide-based phosphors. They are used in fluorescent lamps by doping Eu
3+ (red), Tb
3+(green), and Ce
3+(blue) to produce white light. These lanthanide ions absorb in the UV region by CTS band (Eu
3+) and 4f5d band (Tb
3+ and Ce
3+). The emission is
5D
0 -->
7F
2 (Eu
3+ red) and
5D
4 -->
7F
5 (Tb
3+ green). But Ce
3+ is an exception since its blue emission is also 4f5d transition (also, it's fluorescence unlike Eu
3+ and Tb
3+).
Human eyes only have detection frequency up to 60 frames per second, under the circumstances that you are looking at a flashing light source. That means no less than 16.7 millisecond of light intensity changes can be detected by the human eye (and even longer if you are talking about one single pulse of light). Emission lifetime of Eu3+ (
5D
0 -->
7F
J transition ) in Y2O3 is somewhere around 1 - 3 ms (depending on how they are prepared). So if you turn off the excitation light, the emission of Eu3+ appears to human eye as if it instantaneously stops. In another words,
you can't tell the difference between fluorescence and phosphorescence by human eyes (there are some minor exceptions where some organic phosphors show phosphorescence lifetime of over few seconds).
If you are working on Eu
3+/Yb
3+, my speculation is that you are working on its upconversion properties. By using NIR laser, you are exciting multiple Yb
3+ ions in hope that some of them are going to sequentially transfer its energy to Eu
3+ ion, and exciting it to higher energy level so that it will emit. Basically, you are converting NIR light (lower energy) into visible light (higher energy), hence the term "upconversion".
There are literally hundreds and thousands of upconversion articles out there, and even more about spectroscopic properties of Eu
3+ and Yb
3+ ions. Their quantum mechanical spectroscopic theory was developed by Judd (Phys. Rev. 1962) and Ofelt (J. Chem. Phys. 1962) separately, and they are widely known as the Judd-Ofelt theory. No one working on the optical properties of rare-Earth's should be oblivious to the existence of this theory, so I highly suggest you read them. A less technical but well summarized article of the theory is available by Hehlen (J. Lumin. 2013).
You also might want to check out textbooks for basic spectroscopy and photoluminescence. Also, you should grab an inorganic chemistry textbook and condensed matter physics textbook that covers crystal field theory. Crystal field theory is crucial in understanding lanthanide luminescence, and will also help you understand the Judd-Ofelt theory since that's what the theory bases itself on. Also, Judd-Ofelt theory is a semi-empirical quantum mechanical theory based on spherical tensor techniques. Therefore, you should also refer to any textbook that concerns atomic spectra. Since you are a physics major, a strong quantum mechanics background will greatly help you in understanding them.
Good luck.
