Diagrams (1) and (2) are energy-level diagrams for two different LEDs. One LED emits red light, and the other emits blue light. Which one emits red, and which blue? Explain.(1)
(2)

Verified step by step guidance

1. Identify the energy gap (band gap) between the top of the valence band and the bottom of the conduction band in both diagrams.
2. Recall that the color of light emitted by an LED is determined by the energy of the photons, which is directly related to the band gap energy.
3. Understand that blue light has a higher energy and shorter wavelength compared to red light, which has a lower energy and longer wavelength.
4. Compare the band gaps in the two diagrams: the larger band gap corresponds to the higher energy blue light, and the smaller band gap corresponds to the lower energy red light.
5. Determine which diagram has the larger band gap to identify the LED that emits blue light, and which has the smaller band gap to identify the LED that emits red light.

Key Concepts

Energy Levels and Photon Emission

In semiconductors, electrons occupy energy levels within bands, specifically the valence and conduction bands. When an electron transitions from a higher energy level in the conduction band to a lower energy level in the valence band, it emits a photon. The energy of the emitted photon corresponds to the energy difference between these levels, determining the color of the light emitted.

Wavelength and Color of Light

The color of light emitted by an LED is directly related to its wavelength, which is inversely proportional to energy. Red light has a longer wavelength (around 620-750 nm) and lower energy, while blue light has a shorter wavelength (around 450-495 nm) and higher energy. Thus, the energy-level diagram can indicate which LED emits which color based on the energy gap between the bands.

Band Gap Energy

The band gap energy is the energy difference between the top of the valence band and the bottom of the conduction band in a semiconductor. A larger band gap corresponds to higher energy transitions, resulting in the emission of higher-energy (blue) light, while a smaller band gap leads to lower energy transitions, resulting in the emission of lower-energy (red) light. This concept is crucial for identifying the color of light emitted by different LEDs.