Nanomaterials Standard to Shed Light on Display Applications

Nanomaterials Standard to Shed Light on Display Applications

This piece was originally published in the April 2018 issue of electroindustry.

Mike Leibowitz, Program Manager, NEMA

As lighting devices and displays transition from sources based on heated filaments to ones based on solid state lighting (SSL), lamps and luminaires that use light-emitting diodes (LEDs) are providing light in a wide variety of lighting colors.

To address the essential general and optical requirements of monodisperse luminescent nanomaterials used in general lighting and display products, the International Electrotechnical Commission (IEC) Technical Committee 113 (Nanotechnology for Electrotechnical Products and Systems) will soon publish IEC 62565-4-2 Luminescent nanomaterials—Detail specification for general lighting and display applications.

In display products such as liquid crystal displays (LCDs), white backlights are used in conjunction with filters to provide red, green, and blue. These backlights are also increasingly leveraging breakthroughs in LED technologies to increase the color gamut.

There are several key drivers for this change, including increased energy efficiency, increased product lifetime, flexibility in colors produced, and good color-rendering properties. For example, SSL sources are able to achieve luminous efficacies that are significantly higher than conventional incandescent lamps.

Since approximately 20 percent of the world’s electricity consumption is attributed to providing illumination, the impact of such a large gain in luminous efficacy provided by changing to SSL technologies is significant. Likewise, SSL backlights consume less energy than other backlight technologies, which is especially important in battery-powered portable electronics.

The structures of SSL sources used for general lighting and display backlights often are similar. In a common structure, these devices consist of a blue LED and at least one photoluminescent material to provide one or more additional wavelengths. When energized, some photons emitted by the LEDs are absorbed by the luminescent material and produce secondary photons of different wavelengths through the process of photoluminescence. The light produced by the SSL source is a mixture of the emissions from the blue LED and the photoluminescent material.

Semiconductor nanocrystals like spherical quantum dots, elongated quantum rods, and inorganic nanophosphors are especially advantageous in lighting and display applications because of their broad absorption bands, narrow emission bands, high photoluminescence quantum yields, and excellent photostability.

Generally, luminescent nanomaterials used in lighting and display applications are classified according to excitation spectrum, emission spectrum (including a specific emission peak wavelength and a narrow emission peak shape as measured by the full width at half maximum), quantum efficiency, chemistry, and other factors.

Usually, these properties are achieved in a monodisperse material, with particles of similar sizes. Imparting multiple colors to a lighting or display product may involve the use of nanomaterials of multiple sizes, each of which may be specified individually. As a result of the properties of luminescent nanomaterials, lighting and display devices incorporating these materials can have excellent luminous efficacy and extraordinary color quality.

This new section of the IEC 62565 series of nanomaterial specifications will codify the format for specifying, reporting, and validating the essential properties of luminescent nanomaterials for use in lighting and display products. It will also enable the customer to specify requirements in a standardized manner and to verify through standardized methods that the luminescent nanomaterial meets the required properties.

A bilingual version of this publication may be issued at a later date.

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