Dear Walaa Almasri,

Why do quantum dots emit different colors?

Also known as “zero-dimensional electronic structures,” quantum dots are unique in that their semiconductor energy levels can be tailored by simply altering size, shape and charge potential. These energy levels result in distinct color identifications for different-sized quantum dots.

What is the difference between carbon dots and carbon quantum dots?

The key difference between carbon dots and quantum dots is that carbon dots are small carbon nanoparticles, whereas quantum dots are small semiconductor particles. Both carbon dots and quantum dots fall under the field of quantum mechanics. These are small nanoscale particles.

How is quantum dot size determined?

By measuring the energy of the photons that are emitted, we can determine the size of the Quantum Dots. = [8.52*10-37/(1.99*10-25/λ(m) - 2.15*10-19)]m2. Task: For four different samples of Quantum Dots excite the dots using a 380 nm LED.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6933582/

https://www.researchgate.net/post/Why-there-is-alternate-increase-and-decrease-in-my-absorbance-spectrum-for-carbon-quantum-dot-as-the-time-of-reaction-increasing

Unlike molecules, nanomaterials can show 'aging' (like humans) and can show a change of their properties over time. CdSe nanoparticles are know to show increased emission intensity over time. Gold nanoparticles, in a solid state, are known to 'fuse'. Their intrinsic structure can change over time.

It does not need to be decomposition, it can be 're-structuring'.

Even improved crystal packing.

Some are very stable, like gold nanoparticles in a museum in London, from ~1880, made by Rutherford (or was it...).

Dear colleague

As you know the emission energies of quantum dots strongly depend on their size , then if you have performed scaled images (before and after) you would have had confirmed size changes

regards

Walaa Almasri

For KSA in this direction, you need to study colloidal chemistry. There, the basics of obtaining and properties of dispersed systems are given. Quantum dots, nanoparticles belong to dispersed systems. Due to the large specific surface area, quantum dots are thermodynamically and kinetically unstable. Over time, they unite (enlarge) and settle. This is the reason for the change in the size effect. In your case, the absorption spectrum. You can read the course of colloid chemistry in the form of a dictionary in a summary.

Data Yu.A.Mirgorod, R.V. Grebennikova. Glossary on Colloid Chemistry.

Data Yu. A. Mirgorod, R.V. Grebennikova. Glossary on Physical Chemistry

In general carbon dots have good storage stability. So, first of all, I would suggest you to verify that CD has been synthesized properly. If same happens again even after successful preparation of CD then your CD is not stable in your storage media.

Please note that CD research has many misconceptions and disputes which often mislead research. You may check the following article

Article Are carbon dots worth the tremendous attention it is getting...