Dear Muhammed,

Very interesating but difficult question. First of all, the internal quantum efficiency IQE is indeed the ratio of tau(sample, measured)/tau(sample, radiative). The question is now, how to obtain the radiative decay time? This can be done by experiments, e.g. to prepare a low-doped (e.g. 0.01% Nd, crystalline!!) sample and to measure the decay time at 4 K to freeze in any non-radiative processes. We did this for YAG:Ce and LuAG:Ce and obtained 65 ns and 54 ns respectively. As an alternative you can use J.O.-Theory, however, from internal Philips reports made on the JO-Theory in the 70ties and 80ties I could withdraw that these calculations are rather inaccurate and not useful to obtain to exact numbers. This might explain your discrepancy.

Also keep in mind, that an amoprhous glass matrix is not well defined and that for this reason the internal quantum efficiency of RE activators is typically low (< 10%). This is the reason, why the big lamp companies never doped the glass, but applied a crystalline phosphor layer on top of the lamp glass (bulb or tube) as a coating.

All the best,

Thomas

Muhammad Shoaib

The article will help you

file:///C:/Users/user/Downloads/vliyanie-kontsentratsii-ionov-nd-3-na-spektralno-lyuminestsentnye-svoystva-lazernogo-fosfatnogo-stekla.pdf

Muhammad Shoaib

Try to remeasure the fluorescence lifetime using a powder of the sample.

Dear Muhammed,

Very interesating but difficult question. First of all, the internal quantum efficiency IQE is indeed the ratio of tau(sample, measured)/tau(sample, radiative). The question is now, how to obtain the radiative decay time? This can be done by experiments, e.g. to prepare a low-doped (e.g. 0.01% Nd, crystalline!!) sample and to measure the decay time at 4 K to freeze in any non-radiative processes. We did this for YAG:Ce and LuAG:Ce and obtained 65 ns and 54 ns respectively. As an alternative you can use J.O.-Theory, however, from internal Philips reports made on the JO-Theory in the 70ties and 80ties I could withdraw that these calculations are rather inaccurate and not useful to obtain to exact numbers. This might explain your discrepancy.

Also keep in mind, that an amoprhous glass matrix is not well defined and that for this reason the internal quantum efficiency of RE activators is typically low (< 10%). This is the reason, why the big lamp companies never doped the glass, but applied a crystalline phosphor layer on top of the lamp glass (bulb or tube) as a coating.

All the best,

Thomas

Thank you sir Thomas Jüstel for informative answer

Thomas Jüstel I completely agree with your answer, except the part for the JO analysis. It is accurate up to 20% if and only if it is conducted properly. Maybe Muhammad Shoaib does not have a cryostat to lower the temperature to ~10K, so JO is the only way. I had the same problem with radiative lifetime estimation from JO and the reason was always inaccurate refractive index values. You need to have the exact values for the barycenters of the transitions, i.e. constant n will not do in most of the situations.

Dear Aleksandar,

Thanks for your good point for the discussion. However, as you pointed out the calculation requires accurate refractive index values at the respective wavelength. These data are hard to find for doped samples according to my experience. Moreover, there are cases where the Judd-Ofelt theory of one-photon absorption or emission does not lead to accurate prediction. Some well-known examples are given by the hypersensitive transitions. Moreover, the accuracy depends on the approximations, e.g. whether dynamic coupling, electron correlation, or relativistic contributions are taken into account.

All the best,

Thomas