Most of the articles report PLQY values below %10 for systems radiates through up-conversion mechansim while down-conversion PLQY values reach up to 80-90 %. Is there a theoretical limit?
Photon upconversion is a two photon process. The maximum quantum yield (as measured by an integrating sphere) that you could ever achieve is 50%.
Do you mean spontaneous parametric down conversion SPDC? I am wondering how the PLQY is exactly calculated because real entangled pairs of signal and idler photons are in the ppm range. If you could post a paper as an example I could maybe better understand the difference.
This question is not clear. The Photoluminescence Quantum Yield (PLQY) is not low always. Depends on the system.
Dear Franz-Josef Schmitt ,
I mean the absolute quantum yield that is measured in an integrating sphere.
Article Upconversion photon quantification in Tm3+/Yb3+ doped alumin...
Thank you.
Dear Agnishwar Girigoswami,
Yes it depends on the system for sure but generally absolute quantum yield values of up-conversion systems are lower compared to down conversion ones. I suppose there is no such an up-conversion example that possess over 10-20 % quantum yield. On ther other hand, perovskite QDs show quantum yield values up to 80 % via down-conversion mechanism.
I do not know that SPDC really achieves 90% absolute quantum yield if you observe real down converted photons - however there are further aspects. Fluorescence itself (radiative decay) of an excited state might reach up to 90% in very ideal systems. In upconversion fluorescence we have upconversion (nonlinear) * fluorescence QY while SPDC is a scattering process that demands for accurate phasematching to achieve conservation energy and momentum. So I would not even call SPDC PL in general. If you mean up conversion quantum yield as compared to normal PL then you expect a nonlinear upconversion + PLE probability compared with PLE probability only.
Photon upconversion is a two photon process. The maximum quantum yield (as measured by an integrating sphere) that you could ever achieve is 50%.
I agree with Catherine E Mccusker . When you increase the number of processes you decrease the overall probability for them to happen. Lets take a famous example of Yb/Er. By 980nm excitation you pump Yb which has a great absorbance, but it is with some probability. Then two Yb ions transfer energy to the single Er, each of those processes happens with some probability as well. The overall probability then depends on the system, but must be lower than the downshifting, where you pump directly into the ion of interest, desirably into the level with great absorbance, like e.g. 5L6 level of Eu3+.
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