A primary reason why CDs, DVDs, and Blu-Ray disks contain different amounts of data is that they use different frequencies of light to encode the information. Higher frequency light has shorter wavelengths, which means less space is required for a single bit, such as the 405 nm wavelength of Blu-Ray technology. Researchers have been trying for some time to use zinc oxide to create ultraviolet lasers, and now those at North Carolina State University have succeeded.
Within lasers and LEDs are p-n junctions, where n-type and p-type materials meet. Negatively charged electrons from the n-type material enter the p-type material and there fall into positively charged holes. Provided the holes are at a lower energy level than the electrons, a photon will be released, representing the difference. The trouble with zinc oxide has been that the p-type material was unstable, but the researchers addressed that by introducing defect complexes, where a zinc atom is missing and the associated oxygen atom is replaced with nitrogen and hydrogen atoms.
The reason why so many researchers had been working with zinc oxide to use in UV lasers and LEDs is that it can be made with relatively few undesired defects, allowing it to be quite energy efficient. Fortunately what the researchers discovered does not disrupt that, and also fortunately, it can operate at room temperature.
Source: North Carolina State University