OLEDs in phones & TVs may be used to map magnetic fields

“If this technology is properly developed, people could simply use their smartphones to map the magnetic fields around them, for example, to spot defects in diamonds or jewelry. This also has applications in industry, such as finding defects in construction materials or as a biomedical sensor.”

The device could have important implications in healthcare and industrial sectors

Dr. Geng explains the basic working principle of an OLED device: "...when a voltage is applied, electrons and holes are injected into different layers of the device. When the electrons and holes meet in the central layer, they form ‘excitons’, which emit visible light when they decay, and that’s what makes OLEDs useful as displays and lighting sources.”  

In the press release, the team explains that light emission via an OLED exploits the charge characteristics of electrons, which have a negative charge, and holes, which have a positive charge. They both also have another intrinsic property called spin. Sensitive to external magnetic fields, the spin can flip-flop or switch its direction under magnetic resonance conditions.  

“By measuring the signal change, both in electric current and emission light, induced by such a flip-flop, we are able to detect the strength of any magnetic field the device is exposed to,” says Dr. Geng. 

By integrating an OLED with a microwave resonator, the team made a small oscillating magnetic field across the OLED device, allowing each pixel of the OLED screen to act as a small magnetic field sensor. 

The device uses a camera and microwave electronics to detect magnetic waves, the same method that also enables Magnetic Resonance Imaging (MRI). 

Study abstract:

Quantum sensing and imaging of magnetic fields have attracted broad interests due to its potential for high sensitivity and spatial resolution. Common systems used for quantum sensing require either optical excitation (e.g., nitrogen-vacancy centres in diamond, atomic vapor magnetometers), or cryogenic temperatures (e.g., SQUIDs, superconducting qubits), which pose challenges for chip-scale integration and commercial scalability. Here, we demonstrate an integrated organic light emitting diode (OLED) based solid-state sensor for magnetic field imaging, which employs spatially resolved magnetic resonance to provide a robust mapping of magnetic fields. By considering the monolithic OLED as an array of individual virtual sensors, we achieve sub-micron magnetic field mapping with field sensitivity of ~160 µT Hz−1/2 µm−2. Our work demonstrates a chip-scale OLED-based laser free magnetic field sensor and an approach to magnetic field mapping built on a commercially relevant and manufacturable technology.