JW Fung,

Your question about temperature dependence of EPR spectral intensities will depend on the type of paramagnetic sample of interest and the associated relaxation times.  Moreover, changes in signal amplitude as a function of temperature are different for superparamagnetic than for paramagnetic systems.  As the question is proposed, there is not enough information because EPR spectra behave differently as a function of temperature depending on the (super)paramagnetic species.    

Can you be more specific about your EPR sample?  Also, what is your temperature range?

Robert

Everything depends what equipment you have exactly but generally you will have temperature dependences of g factors, A constants (D, E constants), integral intensities, and line widths and from that you can estimate a lot of things.

Magnetic interaction - integral intensity (magnetic susceptibility) measurements can distinguish samples if they are para- (Curie function, Pauli paramagnetism), super para .... It is possible to study exchange interactions, dipole-dipole interactions, phase transitions, Jahn-Teller effects, distances between dipoles and probably many more.

Relaxation times T1, T2 (related to the line widths), TM in function of temperature can help to distinguish between different mechanisms of spin relaxation, spin and spectral diffusion processes.

For some mentioned above things you will need a pulse EPR spectrometer.

Give us more information about your precise requirements, its a big topic. What chemical systems are you interested in? Organic free radicals, radical ions, inorganic systems, solution or solid state, etc ? What type of equipment do you have? Bruker, Jeol Varian? X-band?

Thank you for everyone's help. I have modified the question and added more information. The equipment tested is Bruker. Please give me more help. Thank you.

I don't know if the sample "P-doped carbon nitride" is conductive or not, but weak integral intensity dependence on temperature can originate from delocalized conduction electrons.

Thank you for Krzysztof Tadyszak's kind help. The P-doped carbon nitride is highly conductive.

Try to read about Conduction Electron Spin Resonance (ESR) articles of Dyson, Feher, Kipp, Kodera

What is implied if the intensity EPR spectra decreased a lot as temperature increased?

According to your input the above, your systems looks like semiconductor material, which can have many different factors for spin transitions and dynamics at different temperatures.

- Boltzman distribution (electron spin)

- interaction between electron spins delocalized in the conduction band and holes in the valence band (electron spins also interact each other)

- their interactions with the host lattice

At higher temperatures, the orientation of electron spin or charge carrier (including the holes) is not conserved for long time,accompanied by a significant spin polarization.

All in all, spin-dependent transport process dominates in semiconductors.

Hope, these are helpful.

Thank you very much for Dr. Amgalanbaatar Baldansuren generous help. It's very helpful to me. Would you be kind enough to introduce some EPR books or papers related to semiconductors?

I am glad my inputs were helpful. I do not recall any specific book about semiconductors. However, there is some new technique so-called EDMR for photovoltaic studies. As you know, photovoltaic is sort of semiconductors and principles of EDMR is similar to EPR. The following is dissertation: Spin-dependent Transport and Recombination in Solar Cells studied by Pulsed Electrically Detected Magnetic Resonance by Jan Behrends (according to Google). You can make request for the author.

Hope this is helpful. 

Dear  Dr. Amgalanbaatar Baldansuren, what's the reference for your answer on the intensity EPR spectra decreased a lot as temperature increased? Thank you for your time.

The intensity of EPR signal are increased with reducing the temperature, attributed to temperature effects on Boltzmann distribution

the increment of the intensity of EPR is associated with the magnetic transition phase may be from para to antiferromagnetic because the spin system in magnetic materials are highly depend on the temperature of the system (curie and niel temperature)