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New Strategy for Making Tunable Photonic Heterostructure Crystals

New levels of miniaturization, speed, and data processing can probably be achieved with optical quantum computers, which use light to transmit information. To achieve this, materials that can absorb and transmit photons are required.

(Credit: Wiley)

In the journal Angewandte Chemie, Chinese researchers have presented a new approach for building photonic heterostructure crystals with adjustable properties. They have created a prototype of a logic gate using a crystalline rod with stripes that fluoresce in various colors.

The group headed by Ze Chang and Xian-He Bu has succeeded by using uniquely built metal-organic frameworks (MOFs)—lattice-like structures composed of metallic “nodes” connected by organic ligands. These structures consist of cage-like cavities that can accommodate other molecules as “guests.”

Here, the guests are matched to a portion of the ligands incorporated into the lattice so that the guests can transport electrons to the ligand molecule (charge transfer). Such systems have a tendency to fluoresce. For a particular MOF, the color of the fluorescence is dependent on the kind of guest.

Another benefit of MOF structures is that their crystallization takes place through the growth of layers onto a crystallization nucleus in one chosen direction. The scientists from Nankai University, Tianjin, the Collaborative Innovation Center of Chemical Science and Engineering, Tianjin and Institute of Chemistry Chinese Academy of Sciences, Beijing (China) were, therefore, able to form rod-shaped crystals.

At the time of crystallization, they changed the varieties of guest molecules incorporated. This led to the production of “striped” rods with separate domains that fluoresce differently. For example, they made rods whose tips absorb UV light and fluoresce blue-green, while the middle portion absorbs visible green light and radiates red light.

As they are in direct contact, energy can be transmitted between the domains, and some of the blue-green photons can be transferred to the middle portion, thus causing it to fluoresce red. Most notably, these rods act as light conductors, implying that regardless of the spot irradiated, part of the fluorescence light is transported through the whole rod to its tips.

Using this kind of crystal as a basis, the scientists created a prototype for a logic circuit with two “entrances” and two “exits”—that is, places where light can be stored or recorded and red and/or blue-green signals produced, respectively. The scientists foresee prospective applications for their MOF crystals in constituents with integrated optical circuits, like on-chip signal processors, optical logic gates, and photonic diodes.


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