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Luminescence

Luminescence? is the emission of light without the emission of heat. Luminescent materials have a variety of stimulus to provoke this reaction, but the term Luminescence? is the general term which refers to the emission of light within the visible, infra red or Ultraviolet regions without the production of heat. The stimulus for light emission is wide ranging for example;

  • Chemiluminescence, result of a chemical reaction
  • Crystalloluminescence, result of crystallisation
  • Electroluminescent, result of electrical charge
  • Trioboluminescence, result of material bonds being broken through mechanical action such as rubbing or scratching
  • Photoluminescence, result of absorption of photons
  • Thermo Luminescence?, result of heat

Fluorescence? and Phosphorescence? are forms of photoluminescence.

The ability to emit light without heat is useful in a range of textile applications, the ability to do so without an external power is a further attraction.

Luminescence? is used as a safety alert in a range of applications, in textiles it is used in clothing to alert to the wearers presence, such as in apparel, sportswear and PPE?, most commonly as the fluorescent strips in the High Visibility vest which are a health and safety necessity in many industrial working environments. Safety is also the paramount reason for their use in textile products across engineering, agricultural and building, in such products as tarpaulins, nettings and covering in order to draw attention to their presence.

The advancement of luminescent materials in textiles has led to an increased interest from the fashion industry, where the technology is no longer viewed as a purely functional attribute. The exploration of novel ways to incorporate luminescent materials has led to some innovative and striking creations. Luminant use electroluminescent fibres to produce a range of products including garments and interiors, requiring a low power input.

Luminous textiles are being explored for interior or architectural textiles implemented as both a design feature and a promoter of well being reacting to sound or temperature to instruct a luminous colour display.

Lumigram pic

Photo courtesy of Lumigram.

What mechanism is used will depend on the required outcome, Photoluminance? requires light in order for it to re-emit it, therefore is only useful in situations where it will be exposed to light, such as reflective strips illuminated by car head lights. If this light exposure is not possible, such as in underground environments experienced in mining, Photoluminance? is not appropriate, therefore other forms must be used such as electroluminance or chemoluminance.

The luminous materials have to be in small solid dust like particles in order to allow the textile structure to maintain its tactile properties such as bending, shearing and drape ability. Luminous properties can be given to textile materials in a variety of ways, generally this can include;

  • Coating fabrics with luminous particles in a resin mix
  • Introduction into synthetic fibres at spinning stage
  • Fibre coating
  • Textile finishing or domestic laundering
  • Use of Optical fibres
  • Use of Light emitting Wires

The coating of textiles with light emitting materials in a resin is perhaps the most widely used in safety garments and this is seen in such items as the strips in high visibility vests, where retroreflective or fluorescent materials are affixed to the textile in a resin. This affects the durability of the textile and can limit its production method, making sewing difficult and limiting end use.

Fluorescent materials in textiles are most widely used as optical brighteners in laundry additives to make whites appear whiter by reflecting the light.

Rare-earth minerals with luminescent properties have been added through a melt spinning process. 

Optical fibres have been modified from those used in data transmission to emit the light being carried along them, instead of just at the ends as displayed in traditional optical fibres, displaying luminous along the length of the fibre. Although optical fibres have been developed as sensors to monitor and transmit data from the wearer, ie, biological readings from military personnel, or from other textile applications such as load stresses in engineering textiles.