The terms nanocrystals, quantum dots, and nanoparticles refer to different types of nanoscale materials, but they have distinct differences in size, crystal structure, and bandgap. Here's a breakdown:

1. Nanocrystals

Size: Typically 1-100 nm in at least one dimension.

Crystal Structure: Nanocrystals are small crystalline particles where atoms are arranged in a regular, repeating pattern (crystal lattice) similar to bulk materials. The overall structure can be single-crystalline or polycrystalline.

Bandgap: The bandgap in nanocrystals is influenced by their size due to the quantum confinement effect. As the size decreases, the bandgap increases, which is different from the bulk material's bandgap but depends heavily on the material itself.

2. Quantum Dots

Size: Typically smaller than 10 nm.

Crystal Structure: Quantum dots are a subset of nanocrystals that are so small they exhibit quantum mechanical properties. They can be single-crystalline, and their small size leads to discrete energy levels (quantization) rather than a continuous band structure.

Bandgap: Quantum dots exhibit a size-dependent bandgap due to quantum confinement, where the bandgap increases significantly as the size decreases. This effect gives quantum dots unique optical and electronic properties, such as tunable light emission (different colours) depending on their size.

3. Nanoparticles

Size: Generally in the range of 1-100 nm.

Crystal Structure: Nanoparticles can be crystalline, amorphous, or even composite. The structure varies widely depending on the material and how it was synthesized. Not all nanoparticles are nanocrystals; they can lack the regular, repeating lattice structure that defines a crystal.

Bandgap: The bandgap of nanoparticles can vary, but they do not always exhibit the same degree of quantum confinement as quantum dots. The effect of size on the bandgap depends on the material's electronic properties, but in some nanoparticles, the bandgap may be similar to the bulk material.

Summary of Differences:

Size: Quantum dots are typically the smallest, with sizes below 10 nm, while nanocrystals and nanoparticles span a broader range from 1-100 nm.

Crystal Structure: Nanocrystals and quantum dots have a well-defined crystal structure, whereas nanoparticles can be amorphous, crystalline, or composite.

Bandgap: Quantum dots exhibit strong quantum confinement effects, leading to a highly size-dependent bandgap, while nanocrystals and nanoparticles may or may not show this effect, depending on their size and material composition.

In essence, quantum dots are a special type of nanocrystals that exhibit pronounced quantum effects, whereas nanoparticles refer to a broader class of small particles, which may or may not have a crystalline structure or a tunable bandgap.

Nanocrystals, quantum dots, and nanoparticles are closely related in the fields of nanoscience and materials science, but they differ in terms of size, crystal structure, and energy gap (band gap).

1. Nanoparticles

• Size: Nanoparticles typically refer to particles with dimensions in the range of 1 to 100 nanometers. The term "nanoparticle" is more general and refers to any particle within this size range.
• Crystal Structure: Nanoparticles can have various crystal structures, depending on the material. They could be amorphous, crystalline, or polycrystalline. The crystal structure is highly dependent on how the nanoparticle is synthesized and its chemical composition.
• Energy Gap (Band Gap): Nanoparticles may not necessarily have a tunable band gap. Their band gap is usually close to that of the bulk material, though quantum confinement effects may start to become apparent as particle sizes get very small (below 10 nm).

2. Nanocrystals

• Size: Nanocrystals are a specific type of nanoparticle with crystalline structure, typically between 1 and 100 nm in size.
• Crystal Structure: As the name suggests, nanocrystals are characterized by their well-defined crystal lattice, meaning they are single crystals at the nanoscale. The structure is typically ordered and periodic, which gives nanocrystals distinct properties compared to amorphous or polycrystalline nanoparticles.
• Energy Gap (Band Gap): The band gap of nanocrystals can be tuned by size due to quantum confinement effects. As the size of the nanocrystal decreases, the band gap increases. This is more prominent in semiconducting materials like CdSe, PbS, etc.

3. Quantum Dots

• Size: Quantum dots are a subset of nanocrystals, typically ranging between 2 to 10 nm. Their small size makes quantum confinement effects extremely significant.
• Crystal Structure: Quantum dots have a crystalline structure, but what distinguishes them is that they are small enough for quantum confinement to dominate their properties. They are essentially zero-dimensional systems where electrons and holes are confined in all three dimensions.
• Energy Gap (Band Gap): The most defining feature of quantum dots is their tunable band gap, which strongly depends on their size. As the size decreases, the energy levels become discrete, and the band gap widens. This allows for precise control over the optical and electronic properties, which is why quantum dots are used in applications like displays, lasers, and solar cells.

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The term "nanoparticle" refers to an object of a certain geometry - all dimensions are less than 1 micron.

Nanocrystal is a nanoparticle that is a mono-crystal

While nanodot refers to an object with confined electronic states. Normally it has to be a semiconductor since a dielectric nanoparticle has no electronic states and metallic nanoparticle will have too many states at the Fermi level

Nanocrystals, quantum dots, and nanoparticles all refer to nanoscale materials, but they differ in their size, crystal structure, and band gap properties.

The attached image below contains the difference between them.

size