Photoluminescent Nanofibers for High-Efficiency Solid-State Lighting

Example of the fabrication of multicolor QD PLNs with excellent resolution using ink jet printing.

Polymer nanofibers are nanoscale materials whose properties can be adjusted to provide desirable light management performance for high efficiency solid-state lighting luminaires. The polymeric nanofibers at the core of this project have diameters on the order of 100 to 1000nm and a length of more than 1cm.

By controlling fiber diameter, fiber packing, and fiber morphology, a low cost, high-performance optical material can be fabricated. This report describes the fabrication of these nanofiber structures and their uses and benefits in solid-state lighting application.

When used in solid-state lighting (SSL) devices, nanofibers can take the form of either diffuse reflectors or photoluminescent materials. Nanofiber reflectors (NFR) were developed which displayed high diffuse reflectance with reflectance values in excess of 0.90. In contrast, traditional reflector materials such as aluminum and paint typically possess reflectance values below 0.80 and absorb a larger fraction of light, reducing luminaire output efficiency. The incorporation of the NFR technology into reflectors, troffers, and beam formers present in SSL luminaires provides better reflectance and lower light loss than is possible with conventional materials.

Picture of four prototype devices incorporating PLNs undergoing testing.

Picture of an automated, roll-to-roll electrospinning tool for the manufacture of large volumes of nanofiber substrates, as would be required for the scale-up of this technology. (Image courtesy of Elmarco USA)

Photoluminescent nanofibers (PLN) can be formed by combining nanofibers with photoluminescent materials such as phosphors and quantum dots (QD). Forming the PLN with the proper combination of green and red luminescent materials and exciting the nanocomposite with a blue light-emitting diode (LED) has been demonstrated to produce high-efficiency (> 55 lumens per watt) white light with excellent color rendering properties. The incorporation of QDs in the PLN is particularly advantageous in that this approach enables the correction of any color deficiencies in the light source without creating unnecessary radiation in the near infrared. Cost models developed during this project have demonstrated that both the NFR and PLN materials can be mass produced at a manufacturing cost of less than $5 per square foot, making it commercially attractive.

To capitalize on the benefits of nanofiber technologies in solid-state lighting, several new remote phosphor reflector configurations were developed in the project. When combined with these unique lighting designs, nanofibers have a number of demonstrated benefits in lighting devices including:

Providing high quantum efficiency down-conversion of LED wavelengths to produce full spectrum white light;
Enabling tunable device structures that achieve colors ranging from warm white to cool white with high color rendering indexes (CRI);
Supplying mass producible, cost-effective solutions for diffuse, high-reflectance light management across the visible spectrum;
Facilitating remote phosphor luminaire designs that increase the lifetime and performance of luminescent materials;
Providing conformability to geometries imposed by the light fixture enabling new lighting designs.

The technologies developed during this program have significant commercial potential, and there has been strong interest in these breakthroughs from the lighting community. It is anticipated that these technologies will begin appearing in commercial products in roughly five years.

This work was done by researchers at RIT International, with teaming members at Donaldson Company, Fujifilm Dimatix, Evident Technologies, and Elmarco USA.