Dear colleagues!
In direct band-gap materials with increasing temperature the increasing probability of exciton dissociation decreases the PL intensity. In indirect band-gaps the increase in temperature should lead to higher number of photons assisting the transition process.
If the PL intensity is modeled as Arrhenius-type process, what does the energy from that fit correspond to?
e.g. I(T)=I0*exp(-Ea/kT)
the value for Ea in my case is just about 20-30 meV which is lower than the exciton binding energy (~80 meV). Interestingly the peak position doesn't shift during the temperature increase.
I am helpful for any hint!
Yours,
Chris
Dear Christoph,
Before we go into the details a few questions:
Which indirect band-gap material are we talking about ?
Is it amorphous, crystalline, polycrystalline?
Do you measure the PL or the PLQY ?
With my best regards
Emil
Dear Emil thank you for your reply!
the material at hand is CH3NH3PbBr3 (or alternatively PbI3). The PL spectrum is a nicely centered gaussian that shows thermal broadening but no distinct shift of the gap (~2.30 eV). Tauc plot suggests that the gap is direct (a*E)^0.5 but there might be change (or contribution) from indirect transitions which are too subtle for the absorption to pick it up at low T
The material can be prepared in 3 distinctively different sizes and forms a regular cubic lattice at RT in all cases. XRD suggests it is highly crystalline but not single crystalline in case 2) and 3)
1) solution grown crystal (mm size)
2) quenched solution grown crystal (um size)
3) colloidal QD (~nm size)
as the size decreases aforementioned effect is more pronounced, so it might have some size-dependence.
in this measurement the PL was recorded using a weak laser excitation source 405 nm.
yours & mit besten Gruessen,
Christoph
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Semiconductor