White LED System Research Articles

Four-component, white LED with good colour quality and minimum damage to traditional Chinese paintings

A correlated colour temperature tunable, four-component, LED system suitable for illuminating traditional Chinese paintings painted with inorganic pigments (iop-TCPs) has been designed. This light source can meet the requirements for protective illumination and colour quality in museum illumination. The damage to iop-TCPs caused by the individual 450 nm, 510 nm, 583 nm and 650 nm monochromatic LEDs used to construct the LED system were obtained through a long-term illumination experiment. Then, we calculated the damage resulting from the corresponding four-component white LEDs with various spectral power distributions, the intensities of which were iterated by a brute force algorithm. The constructed spectral power distributions were evaluated by the damage and colour quality formulae. The results showed that the better colour quality spectral power distributions with higher correlated colour temperatures cause less damage to iop-TCPs. The lowest damage spectral power distributions, satisfying colour quality requirements with correlated colour temperatures ranging from 2700 K to 4000 K, were obtained by calculating the corresponding parameters of the formed spectral power distributions and further selection. This paper not only provides a colour temperature tunable, four-component, white LED system suitable for illuminating iop-TCPs but also sets out a methodology that can be used to identify white LEDs suitable for other cultural relics based on damage limitation and visual requirements.

Studies on Föster Resonance Energy Transfer in Blends of Thienylene Vinylenes for White Light Emitting Diodes

Conjugated polymer blends are widely used for realization of white light emitting diodes (WPLEDs). The theoretical understanding of the transfer of energy from high band gap host to the low band gap dopant is very important for designing an efficient and stable white LED system. Novel geometric isomers of thienylene vinylene are studied here for resonant energy transfer between the components of the blends. In this study we report a novel methodology for a simple and pictorial depiction of resonant energy transfer between conjugated polymers in blend for a quick screening of prospective constituents prior to synthesis of these polymeric materials. The resonant energy transfer is also supported by the experimental observations which show a spectral overlap. The sequence of energy transfer predicted by theory is in agreement with the order of band gap of the constituent polymers. The resulting fluorescence spectrum of the blends gave a broad emission in the visible region and is of great significance in the development of white light emission.

Nanocrystalline Phosphors for Lighting and Detection Applications

We report the development of new nanoparticle phosphors and quantum dot structures designed for applications to enhance the color rendering and efficiency of high brightness white LEDs, as well as for bio-sensing applications. The intrinsic problem of self-absorption, high toxicity, and high sensitivity to thermal quenching of conventional quantum dot systems has prevented their adoption to LED devices. Doped Cd-free quantum dots may circumvent these issues due to their distinct Stokes shift and improved stability at high temperature. We report on the modification of Mn-doped ZnSe/ZnS core-shell quantum dots for application to the (blue diode + yellow emitter) white LED system. Band gap tuning for 460 nm excitation, inorganic shell growth and in-situ monitoring for enhanced efficiency, and analysis of thermal stability will are reported.