@Maria Bernechea ,Thanx mam.

I agree with Maria Bernechea. In generally, QDs are luminescent semiconductor nanocrystals with diameters of 2-20 nm, and made of different element groups, such as III-V, II-VI, and I-VII. When we talk about QDs，we mainly associate and focus on its unique optical and electronic properties, such as size-dependent fluorescent emission. However, nanoparticle, more like a descriptive nouns, which only required the object size in the range.

If the particle size is more than Bohr exciton radius why particles do not come in the regime of quantum confinement ?

I agree Maria and Mian.

QDs are quasi-zero dimension aggregates of atoms of semiconductor materials that produce a crystalline matrix (nanocrystal) whose radius is smaller than the bulk exciton Bohr radius and constitute a class of materials intermediate between molecular and bulk forms of matter. Due to their typical dimension in the nanoscale (2-10 nm), they suffer a phenomena called quantum confinement, in which their electronic states are discrete, and allow to tune their emission in a size-dependence manner.

Meanwhile the term nanoparticle takes all the material below 1 micron.

QD are generally fluorescent but NPs are non-fluoroscent in nature. due Size confinement below the Bhor-excitaion radius quantum effects startsi.e. continuous enegy level separated in discrete one. Its not true at all NPs below 10 nm should behave like QD. There energy gap separation depends on material of choice. we will not have QD of silver NPs at a radius 2-6 nm, but u can have CdS QDs at that range.

for reference u can go

http://pubs.acs.org/doi/abs/10.1021/ja3112109?prevSearch=kalyanasis%2Bsahu&searchHistoryKey=

http://www.deepdyve.com/lp/elsevier/a-facile-synthesis-of-high-optical-quality-silver-nanoparticles-by-Xhtzyvqfbn

For QDs, electronic energy levels should be quantized (discretized) in all 3D of the nanoparticle. In other words, in a nanoparticles energy levels quantization may be occurred only in one or two dimensions.

QDs and nanoparticles are nano size materials. But, QDs are semiconducting materials. Nanoparticles means metallic particles.

In case of silver nanoparticles, we talk about interband  and intraband transitions , which means that there is quantization of energy states.  Wonder why do we not use the term QD for these nanoparticles?

both r on nano scale,but i think the basic difference is that QD having crystalline structure but while discussing about nano particles it is only the matter of size but not structure.

Quantum Dots and nano particles are arise in nano scale (0D). Quantum Dots are semiconductor but nano particles are metallic in nature. (Eg. CdS - semiconductor, Ag - nano particles)

Nanoparticles (NPs) - this is the most general term to call a small particle as big as nanoscale size. We say NPs when we a priory aren't sure if there is quantum confinement effect (QCE). Though we still expect some new physical properties in comparison with bulk material otherwise there is no need to go to such a small scales. However, on my opinion NP means nothing less but the size nano.

Then Nanocrystals (NCs) - this means NPs with crystalline core

Quantum dots (QDs) - they called quantum bcz quantum effects start to play an important role at nanoscale size. I think historically QD imply quantum confinement effect (QCE). Though later it occurs that in both direct and indirect bandgap semiconductors there might be indirect fluorescence transitions (accompanied by phonons) while the QCE is still present. Sometimes we even don't know if there is QCE in that case it's better to avoid the term QDs.

Moreover, above mentioned definitions are not yet finally evolved and even NCs with confirmed QCE are often called NCs (not QDs) because of historical reasons (for instance, Si NCs).

Concerning sizes: all depends on exciton Bohr radius for the specific material. Then we distinguish weak, mediate and strong QCE depending on whether all carriers or only some of them are quantum confined. Most of II-VI and III-V compound semiconductors have small Bohr radius - then QDs must be really small (lets say less than couple of nm).

I satisfied with the above description. But, the information in the aspect of wavefunctions change in quantum regime will give more support to the description.

I Pleasant of Mrs. mar descriptions, but I would like to know more about differences of quantum Dot and Nanoparticle against light and Radiation as a Detector.

@Maria Bernechea ,Thans

Your explained about quantum Dots is very simply and useable. I would like to read all notes in physic .sincerely

The most important property of the quantum dots that they are two dimensional material assembly with quantum mechanical dimensions for the quantum confinement of the motion of electrons in the conduction band and holes in the valence band and so one can trim the band gap of the material.

The nonparticipants are three dimentional structure with nanometer dimensions. If the dimentions are causing appreciable confinement then the nanoparticle will have quantum mechanical confinement. If the dimensions are smaller than the De Broglie wavelength the quantum mechanical properties will be observed.

Best wishes

Dear Navneet,

The difference is not primarily in the size of the particle,rather is in the properties and geometry of the problem. All quantum dots are Nanoparticles, but not all Nanoparticles are quantum dots.

I work WITH metallic nanoparticles of different sizes(quantum region). For having quantum dot properties we should be in the quantum regime, in this case the size should be smaller than 10 nm (Bohr radius). You can have FOR example silver nanoparticles with 20 nm radius and they will not behave as quantum dots. Once the size is smaller than 10 nm then you are in the quantum regime and we will see, for example, band gap variability with size. Silver nanoparticles with sizes bigger than 10 nm will have the same band gap (around 0.6 eV), the same than in bulk. With sizes smaller than 10 nm the band gap will increase as the size decreases.In this region,there are phenomena that would be exhibited which cannot be explained classically .Therefore,you need to use quantum based theory to do so..This region is when you have the length or size of the particle less than 10nm.

Hope this helps.

Best regards,

Lateef.