The organic down-conversion material then emits radiatively at a rate above nonradiative FRET rate, effectively stopping a reverse transfer process. The most significant benefit using OLEPs instead of phosphors as down-conversion materials is that the efficiency of the color conversion can be significantly enhanced through a nonradiative Förster resonant energy transfer (FRET) mechanism, (5-16) which cannot be achieved using any existing phosphors. OLEPs can therefore simplify the process of fabricating white LEDs, which is particularly attractive to industry. (5) Unlike any existing phosphors which are normally prepared in a form of grains with a typical size of tens of micrometer, OLEPs can be dissolved in a solvent, obtaining homogeneous microstructures simply by means of standard spin-coating techniques widely used in the field of semiconductor optoelectronics. The issues of self-absorption are also eliminated by using OLEPs as a result of their intrinsically large Stokes-shift (>100 nm). A resulting hybrid device therefore features the respective high-performance electrical properties, ultrafast response and photoluminescent (PL) quantum yield of the inorganic and organic material systems, (4) expecting to demonstrate superior performance to current state-of-the-art white LEDs. The basic arrangement achieving white light emission involves the partial down-conversion of an electrically injected blue InGaN/GaN LED by yellow OLEP. A hybrid organic/inorganic III-nitride white LED therefore combines the complementary advantages of the two major semiconductor material groups. (3) OLEPs however suffer from a number of fundamental problems, in particular poor electrical properties.

Furthermore, the much faster response times of organic materials, in comparison to existing phosphors, offers particular advantages in ultrafast Li-Fi. Organic light-emitting polymers (OLEPs) have been developed rapidly in recent years due to a number of advantages, such as high luminescence efficiencies, solubility, low cost manufacturing and flexibility. (1) A receiver however would typically use blue filters to remove the slow-response of the phosphors’ yellow light, (2) resulting in a significant loss (∼50%) to signal intensity. Furthermore, another fundamental limitation for the utilization of such a white LED is due to the very slow response time of phosphors, typically on the order of microseconds, restricting the bandwidth to below 1 MHz for Li-Fi applications. However, the approach has a number of drawbacks, such as the self-absorption of the phosphor, limiting the color-conversion efficiency from blue to yellow wavelengths and thus severe color rendering issues, the issues on quenching and stability of the phosphors, and so on. So far, the current state-of-the-art remains founded on the well-known “blue LED + yellow phosphor” approach, depending on blue emission from InGaN/GaN LEDs radiatively pumping down-conversion phosphor materials that provide longer-wavelength yellow emission that generate together white lighting. The last two decades have seen tremendous progress in developing solid-state lighting, based primarily on III-nitride semiconductors. In this case, a white light source of special characteristics is required in order to meet the multiple-function requirements.

An optimized white-light EL emission is achieved with typical CIE color coordinates at (0.29, 0.32).Īnalogous to the technological development of the conventional telephone to smartphones, lighting is expected to experience a similar evolution leading toward “smart-lighting” that is utilized simultaneously in general illumination and ultrafast high-bandwidth visible light communication (VLC, i.e.

This results in a typical FRET efficiency of 16.7%, where the FRET interaction area accounts for approximately 0.64% of the remaining blue-emitting inorganic LED, but enhancing total device efficiency. A reduction in the recombination lifetime in the InGaN/GaN blue active region has been observed with the hybrid device, confirming the nonradiative FRET process occurring between the InGaN/GaN blue active region and the yellow organic polymer. The hybrid LED geometry significantly enhances proximity between the inorganic active-region and the down-converting yellow organic light-emitting polymers (OLEPs), enabling the near-field nonradiative Förster resonance energy transfer (FRET) process with high efficiency while retaining excellent electrical characteristics of an unpatterned planar LED. An electrically injected hybrid organic/inorganic III-nitride white light-emitting diode (LED) has been fabricated by using a two-dimensional (2D) microhole array structure.

Smith micro amberlight