When calculating the critical distance Rc, defined by Blasse as the distance for which the transfer probability equals the emission probability, how do you know which is the critical concentration? The formula is the following:
Rc= 2* (3*V/(4pi*xc*n))^(1/3), where V is the volume of the crystalllographic unit cell, xc the critical concentration and n the number of lattice sites that can occupied by the activator ions.
Thanks in advance,
José
I don't remember how it was defined in the book, was it the probability of transfer to the neighboring ion of the activator or the transfer to the killing site through several swaps of excitation energy? Usually, the critical concentration is the one at which the efficiency/brightness of emission starts to descrease for increasing the concentration of the activator.
First of all, thank for your reply. Initially i also considered that, but very recently i have seen some articles where they define the critical concentration, as the concentration at which the luminescence intensity I0 of the sensitizer drops to half when you introduce the activator. My problem, is that my sensitizer and my activator are the same ion (Dy3+). Keeping this in mind, i have now 2 options: I can define the I0 as the maximum intensity, and then see at which concentration i have I0/2; or i define I0 as the intensity at a very low concentration (1%), to make sure there isn't any energy transfer. What do you think?
As you have a modoped compound, I would not use a definition of critical concentration for the one containing sensitizer. Practically, you can use the concentration where the concentration quenching start to decrease the intensity of luminescence. If you want to dig deeper, you could also seach for the concentrations, where the decay curves are no more single exponents, but I think even this is not necessary. The concentration corresponding to the maximum effeciency is the best choice.
Thank you for your reply Roman. On your first comment you mention a book. Could you be kind enough to tell me which is it? It's not easy to find decent literature about this subject.
I thought you took the model from it, it is one of the best textbooks on luminescence:
Blasse G.; Grabmaier, B. C. Luminescent materials. Springer: Berlin, etc., 1994
No, i went straigth to Blasse article. Thank you so much for your replies.
How can we consider volume of unit cell for different compounds...???
either by directly seeing the value in the JCPDS cards or by calculating the lattice parameters and then getting volume from those values...
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