It is possible to reach new levels of miniaturization, speed and data processing with optical quantum computers that use light to transmit information. For this we need materials that can absorb and transmit photons. In the diary Angewandte Chemie, Chinese scientists have introduced a new strategy for constructing tunable photonic heterostructural crystals. Using a crystal rod with bands that fluoresce in different colors, they have developed a prototype logic gate.
The team, led by Zhe Chang and Xian-he-Bu, succeeded in using custom-built metal-organic frameworks (MOFs) – similar to lattice structures made of metal "nodes" bridged with organic ligands. These structures contain cell-like voids that can hold other molecules as "guests". In this case, the guests and some of the ligands integrated in the lattice are aligned so that the guests can transfer electrons to the ligand molecule (charge transfer). Such systems tend to fluoresce. The fluorescence color for a MOF depends on the type of guest.
Another advantage of MOF structures is that their crystallization occurs by increasing the layers on the crystallization nucleus in one preferred direction. In this way, researchers from Nankai University, Tianjin, the Center for Joint Innovation of Chemical Science and Engineering, Tianjin and the Institute of Chemistry of the Chinese Academy of Sciences, Beijing (China) were able to produce rod-shaped crystals. During crystallization, they vary the types of guest molecule involved. This has led to "striped" sticks with separate domains that fluoresce differently. For example, they produced rods whose edges absorb UV light and fluoresce blue-green, while the center absorbs visible green light and emits red light. Because they are in direct contact, energy can be transferred between domains, and some of the blue-green photons can be transmitted to the central part, thereby leading to fluorescent red. Most importantly, these rods behave as conductors of light, which means that no matter where it is irradiated, some of the fluorescent light is transmitted throughout the rod to its ends.
Based on this type of crystals, the researchers developed a prototype for a logic circuit with two "inputs" and two "outputs"; that is, places where light can be stored or recorded and red and / or blue-green signals are generated accordingly. The researchers envision potential applications for their MOF crystals in components with integrated optical circuits, such as photonic diodes, signal chip processors, and optical logic gates.
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