Photon Excited State Energy Transfer Green Light into Blue

Photon up conversion can be more efficient use of burning laser light: two photons into a higher energy of a photon. Now researchers at the Karlsruhe Institute of Technology (Kit) showed for the first time that is installed on the surface of the metal organic framework (surface-mounted metal-organic frameworks, SURMOF between the internal interface is very suitable for this purpose -- they will be green into the blue. The findings, published in the journal advanced materials, bring new opportunities for photovoltaic applications such as solar cells or light emitting diodes.

Metal organic framework is a highly ordered molecular system composed of metal clusters and organic ligands. In the interface function of the Karlsruhe Institute of Technology (IFG), researchers developed in epitaxial growth on a surface of a substrate metal organic framework. These surface mounted metal organic framework can be through a variety of materials to manufacture and use of different pore size and chemical functionality customized, which makes them suitable for a wide range of applications, such as sensors, catalysts,20000mw laser pen， diaphragm, and in medical technology or equipment as the intelligent storage elements.

Another application field is an optoelectronic device, which is a device that converts light into electrical energy or in turn converts electric energy into light. Most of these devices are based on the work of the semiconductor. "The surface mount metal organic framework combines the advantages of organic semiconductors and inorganic semiconductors," said W Christof, director of the functional interface Research Institute, Professor LL. "They have the characteristics of chemical diversity and crystallization, so that we can create an orderly heterogeneous structure." In many optoelectronic devices, a structure that is called the interface layer between the two different semiconductor materials controls the energy transfer between the excited states. Study on micro - structure at the Karlsruhe Institute of Technology (IMT) researchers now produced a new piggyback type SURMOF. Among them, the second layer SURMOF at the top of the first layer of a layer and a layer of the epitaxial growth. In this heterojunction, we can achieve the conversion of photons, the two low energy photons into higher energy photons, in fact, it is equivalent to the integration of them together. "This process turns laser 3000mw light into blue light. The wavelength of the blue light is shorter, and the energy of the photon is bigger. This is very important for photovoltaic applications, "said Richards Bryce, director of the Institute of micro structure technology. Scientists have reported their work in the advanced materials (Materials Advanced), "advanced materials" is one of the top journals in the field of materials science.

Karlsruhe, the researchers demonstrated the photon conversion process is to establish a basis in the so-called triplet annihilation. Two molecules are involved in this process: the sensitizer molecules absorb photons and generate triplet excited state, receiving the state transmitter molecules excited by the triplet triplet annihilation issued a higher strongest laser pointer than the original absorption of photon energy of photons. "The challenge we face is to generate the process as efficiently as possible," said Dr. Howard Ian, head of the Institute of micro structure technology. "We match the sensitization and emitter layers in a manner that is able to obtain both a low conversion threshold and a higher light efficiency."

Since the three state transition is based on electron exchange, the researchers reveal that the photon up conversion process includes an electron transfer process across the interface between the two SURMOF. This puts forward a hypothesis that the SURMOF-SURMOF heterojunction is suitable for many laser 5000mw optoelectronic applications, such as LED and solar cells. One of the limitations of today's solar cells is that they can only use photons with a certain minimum energy to generate electricity. By using the photon up conversion, photovoltaic system can become more efficient.

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