Perovskite lasers - Page 4

EPFL researchers have designed a new type of inorganic nanocomposite that makes perovskite quantum dots (nanometer-sized semiconducting materials with unique optical properties) exceptionally stable against exposure to air, sunlight, heat, and water.

Quantum dots made from perovskites have already been shown to hold potential for solar panels, LEDs and laser technologies. However, perovskite quantum dots have major issues with stability when exposed to air, heat, light, and water. The EPFL team has now succeeded in building perovskite quantum dot films with a technique that helps them overcome these weaknesses.

Researchers at Los Alamos National Laboratory and their partners are creating innovative 2D layered hybrid perovskites that they say can allow greater freedom in designing and fabricating efficient optoelectronic devices. Industrial and consumer applications could include low cost solar cells, LEDs, laser diodes, detectors, and other nano-optoelectronic devices.

They explain that these materials are layered compounds, or a stack of 2D layers of perovskites with nanometer thickness (like a stack of sheets), and the 2D perovskite layers are separated by thin organic layers. "This work could overturn conventional wisdom on the limitations of device designs based on layered perovskites", the team says.

Researchers at Nanyang Technological University in Singapore have fabricated high-performance green light-emitting diodes based on colloidal organometal perovskite nanoparticles. The devices have a maximum luminous efficiency of 11.49 cd/A, a power efficiency of 7.84 lm/W and an external quantum efficiency of 3.8%. This value is said to be about 3.5 times higher than that of the best colloidal perovskite quantum-dot-based LEDs previously made.

The team developed a simple way to make a series of colloidal (CH3NH3)PbX3 nanoparticles with an amorphous structure that can be tuned to emit light in the ultraviolet to near-infrared range. They studied the photoluminescence properties of the nanoparticles and found that the PLQE of the perovskite NP film is much higher than that of the bulk film. They then made the highly efficient green LED.

Researchers from the King Abdullah University of Science and Technology (KAUST) have designed a system that uses an innovative color converter based on luminescent materials known as phosphors, which are commonly used in LED lights, and combines them with nanocrystals of perovskite. This system has achieved record bandwidth, providing a data transmission rate of 2Gbit per second.

The major achievements in this work are breaking the record for data communication using visible light and, even more impressively, producing white light with a very high color-rendering index of 89, by designing a special color converter based on hybrid perovskite nanocrystals. The work demonstrates white light as both a lighting source and a system for ultra-high-speed data communications.

Scientists at Syracuse University and Brookhaven National Laboratory found a new way to visualize and monitor chemical reactions in real time using perovskites. They have designed a nanomaterial that changes color when it interacts with ions and other small molecules during a chemical reaction, allowing to monitor reactions qualitatively with the naked eye and quantitatively with simple instrumentation.

The researchers explain that many chemical reactions occur in a solution that is colorless and transparent so the only way to know if a reaction has occurred or not is to perform extensive analysis after a multi-step purification. This new method represents a simpler way to investigate why and how fast a reaction occurs (if at all). The group has designed a nanoparticle that reacts with by-products of the reaction. When the reaction occurs, the nanoparticle fluoresces at a different color, allowing to gauge kinetics by eye, instead of using special equipment.

Researchers at the University of California at Berkeley and the Lawrence Berkeley National Lab have made novel high-performance and robust lasers from caesium lead halide perovskites nanowires, that could be used in on-chip photonic and spectroscopic applications, such as optical communications, imaging and sensing. The lasing color of the devices can also easily be tuned from green to blue by changing the halide ion.

Nanowire lasers show great promise as miniaturized light sources for optoelectronics. Since they act as both the laser cavity and gain medium, nanowires can be easily incorporated into electronic circuits. Optical gain is the ability of a material to 'amplify' light or to generate more photons than the number of photons it absorbs. A typical laser usually consists of a gain medium encased in an optical cavity containing two opposing mirrors. The gain medium contains two electronic energy levels, and the lower energy level naturally contains more electrons than the upper level. However, by exciting the cavity ' either electrically or by using light ' some electrons can be 'pumped' into the upper state.

Scientists at Nanjing University of Science and Technology, China, and colleagues have used quantum dots based on perovskites for QD-based light-emitting devices (QLEDs). These (completely inorganic) materials reportedly solve the stability problem of previously developed hybrid organic'inorganic halide perovskites.

Quantum dots (QDs) are nanometer-sized semiconductor materials with highly tunable properties such as bandgap, emission color, and absorption spectrum. These characteristics depend on their size and shape, which can be controlled during the synthesis. The quantum dots' luminescence wavelength can be tuned by both their size and by the halide ratio. In this research, the team made blue, green, and yellow QLEDs with high quantum yields, using the perovskite quantum dots as the emitting layer. The researchers state that this development could allow the design of new optoelectronic devices, such as displays, photodetectors, solar cells, and lasers.

Researchers at Ludwig Maximilian Univ. of Munich, Germany (LMU) have succeeded in synthesizing perovskite nanocrystals in the form of ultrathin nanoplatelets whose emission characteristics can be tuned by altering their thickness. The resulting nanoplatelets are about 300 times thinner than the perovskite films conventionally used in the fabrication of solar cells.

Despite their large surface area, these platelets emitted an intense blue luminescence, and the properties exhibited by these minuscule particles were deemed inexplicable in the context of classical physics. The scientists state that they can be accounted for only by the laws of quantum physics, as confirmed by theoretical calculations carried out by the team.