as in all experimental measurements it depends on the material you are studying and on the informations you are looking for.... I can give you some insight on semiconductor nano structures, that are my main research interest:

1) at LT carriers are effectively frozen, so you should be able to see more clearly lowest energy states. At RT carriers can thermally escape to higher energy levels, so you might see other peaks

2) For the same reason carriers at RT can have enough energy to get to non-radiative recombination centers, so, in general, you should expect a strong reduction of the intensity of the PL signal

3) excitonic effects are more efficient at LT, although in some cases you can see excitonic effects: it depends on the exciton binding energy of the system that is material and size-dependent (one very known case is that of InAs QDs)

In general, than, it is easier to get some signal from PL at low temperature than at room temperature...

My final advice is that you measure both PL at low temperature and at room temperature (if you have signal) and you can get much more information by comparing the two spectra.

And than, if you really want to maximum from PL characterization, you could measure PL spectra at different temperatures (maybe in 10° steps) and get other interesting information by studying peak energy, fwhm and Integrated Intensity changes as functions of Temperature

Firt difference is about effective band gap energy. the low temperature band gap energy higer than high temperature. if you want, you can calculate (Tempereture dependent band gap energy) Varshni's emprical law.

The other difference full wight high max.(FWHM) value of PL signal. FWHM increases with Temperature increasing. And traps effectiveness cam be change with differance lattice temperatures. Actually there are very differences but these are basics.

Many processes in materials are temperature dependent: multiphonon relaxation, thermal quenching, thermally stimulated photoionization etc.

In case of metallic nanostructures, low temperature PL is much better to access its intrinsic properties due to temperature-dependent optical losses of the structures.

Hi,

Temperature dependent bandgap doesn't follow Vegard law as Fahrettin mentioned. Vegard's law gives you linear dependence but temperature dependence of bandgap is not linear. You should look for Varshini's paper published several decades back in Physica B for temperature dependent bandgap.

One cannot say which one is better LT or RT both might give useful information. Typically to get more intrinsic optical properties LT PL can help a lot. But RT PL is also equally important because the final device that you would like to make with these nanostructures operate at RT and you certainly want to know their RT properties.

Sorry about that Thaks Dhamodaran that's my mistake. I wanted say Varshni's emprical laws. I used Varshni's law and Vegard's law for different subject and I mispronounce. Yes should have been Varshni .

as in all experimental measurements it depends on the material you are studying and on the informations you are looking for.... I can give you some insight on semiconductor nano structures, that are my main research interest:

1) at LT carriers are effectively frozen, so you should be able to see more clearly lowest energy states. At RT carriers can thermally escape to higher energy levels, so you might see other peaks

2) For the same reason carriers at RT can have enough energy to get to non-radiative recombination centers, so, in general, you should expect a strong reduction of the intensity of the PL signal

3) excitonic effects are more efficient at LT, although in some cases you can see excitonic effects: it depends on the exciton binding energy of the system that is material and size-dependent (one very known case is that of InAs QDs)

In general, than, it is easier to get some signal from PL at low temperature than at room temperature...

My final advice is that you measure both PL at low temperature and at room temperature (if you have signal) and you can get much more information by comparing the two spectra.

And than, if you really want to maximum from PL characterization, you could measure PL spectra at different temperatures (maybe in 10° steps) and get other interesting information by studying peak energy, fwhm and Integrated Intensity changes as functions of Temperature

Thanks to all. The discussion is more useful to me for detailed understanding of LT PL and RT PL.

I addition to above mentioned answers. I would like to draw attention to the strong increase of the exciton (electron) - phonon interaction at room temperature. This leads to a strong broadening of the photoluminescence bands and the overlapping of bands with close energies. Therefore, it is difficult to analyze the structure of the photoluminescence spectra, which are shown at both low and room temperatures. The study of the temperature dependence of photoluminescence bands can provide information about the process of exciton (electron)-phonon interaction. It should also noted, that when the temperature is greatly increased the efficiency of the transitions with absorption of phonons also increase and this leads to a broadening of the bands. Therefore, even in case of deep impurity levels, the ionization energy of which is much greater than the thermal energy, the investigations at the low temperatures are more efficient.

Exactly Youriy Gnatenko has got the point. LT measurements are more efficient and when there is no LT, RT is used.

Measurement of LT PL spectra depends on the purpose of the experiment. Due to limitation of system resources LT PL spectra are not always easy to obtain. For example, impurity related transition in solid state materials doesn't vary much with temperature (there are some exceptions such as Sm2+), whereas defect related PL spectra can show temperature dependence. Appearance of zero phonon lines or vibronic structure may be possible at a temperature lower than 100 K. From the temperature dependence data of the defect related vibronic PL band, some physical parameters such as Debye temperature, Huang- rhys factor may be obtainable.

Suppression of Phonons takes place significantly at LT and hence enhanced PL is observed at 77K or below for most of the solid state materials.

From my experience, very hard to get RT-PL unless the layer is very high quality grown. Most of the time only can get at LT.

to study the intrinsic properties of nanostructures it's better to study them at LT as previously explained. However to optimize the nanostructures for realistic applications, one has to see their emission energy at RT.

RT measurements give broad peaks with reduction in intensity while LT measurements give more specific results