Diversity of microenvironments of the ground state for one. Are these solutions, solid state, or??

This refers to solid state samples. The environment should be consistent apart from the increase in doping of the active ion. Thanks

The purity is one factor in the broadening of spectral peaks. Further, the speed of scanning may cause overlap of nearby peaks with the analytical peak and result in broadening.

There are many reason for broadening of the spectra. For example size distribution, defects (surface,- or point defects), temperature, scattering etc. Depend on your materials and the complex system you measure.

Thanks for all the answers and for suggesting possible causes.

I would hope that the impurities that are present would be low and at least constant for all the samples prepared. The scanning speed (integration time?) is consistent for all measurements using the spectrofluorimeter. However, I was under the assumption that this would only affect S/N ratio unlike varying the slit widths of the monochromator which would reduce the spectral resolution.

The material is a milled phosphor powder so size, scattering and temperature should also be consistent. Furthermore, if the procedure is consistent then this would not explain an increase proportional to the doping of the active ion.

Is this not an ensemble effect due to the increase in ions and hence a change in the dipole position caused by a change in the environment? Or should the lattice possitions always be the same and therefore the local environment is preserved?

In solids samples at room temperature phonon vibrations would cause broadening of luminescence emission. However, at low temperature namely due to absence of thermal phonons, peaks are narrowed down.

In most cases, molecules/ atoms return from the excited state back to the initial ground state. However, in some cases, a small number of molecules may undergo a photochemical reaction which alters whole of the chemical structure of the molecule. If such photo chemically active molecules absorb light, then the probability is that this small number of molecules will not return to the initial state called (educt), but rather switches over to a new ground state called (product) whose absorption spectrum is much different from the (educt). The corresponding inhomogeneous bands do not even overlap and occur over a range of frequencies causing shift (blue or red) of the [S1 ← S0] absorption band depending upon whether their energy difference increases or decreases and hence the name line broadening.

Practically, it is possible to produce such photochemical transformations only in a small group of molecules having Zero Phonon Line (ZPL) frequency. The remaining molecules which do not possess ZPL frequency get bleached as they react with molecular oxygen to yield a free radical singlet oxygen species.

The amount of photo bleaching is a function of the molecular oxygen concentration and the distance between the fluorophore and oxygen molecules. Photo bleaching can be reduced by limiting the exposure time of fluorophores to illumination or by lowering the excitation energy. However, these techniques also reduce the fluorescence signal.

Dear Sean,

Can you recommend some articles with practical examples (spectra) about a broadening of the absorption spectra in inorganic materials ?

The line broadening can be attributed to unintentional variation in the confinement energy in different regions of the well (QW).

The broadening of the absorption spectra could be due to the plasmon surface resonance also.