A brief intro to the luminous world of LEDs…

• LED – Light Emitting Diode

• A two lead semi-conductor light source

• A basic PN junction diode

• Colours available : Blue Green and Red

• Working principle : Electroluminescence

• Applications : Wide variety of applications in electronics and illumination engineering

LEDs and the colour Blue

• Gallium nitride (GaN), which is the material used to create blue LEDs, is hard to grow.

• GaN is a wide band gap semi-conductor.

• Blue is one of the basic colours necessary

to make White light.

• Oct-7 2014, Nobel prize was awarded to

the inventors for their illusive contribution

to the world of light .

LEDs came a long way…• 1907 – Discovered electroluminescence – HJ Round

• 1927 – Created first LED – Oleg Losev

• 1955 – Infrared emission from GaAs – Rubin Braunstein

• 1962 – First visible spectrum (Red) LED – Nick Holonyak

• 1972 – Yellow LED – M. George

• 1972 – First blue-Violet LED – Herb Maruska and Wally Rhines

• 1994 – First high brightness blue LED (InGaN) – Shuji Nakamura

• 1995 – P-Type doping of GaN – Isamu Akasaki & Hiroshi Amano

• 2014 – Nobel Prize in Physics for the invention of blue LED - Isamu Akasaki Hiroshi Amano & Shuji Nakamura

• 2014 – 5 of us just stepped into these footsteps

Hiroshi Amano Shuji Nakamura

The Genius behind the Blue LED…

Isamu Akasaki

Principle…

• LEDs create light by electroluminescence in a semiconductor material

• Electroluminescence - optical phenomenon and electrical phenomenon in which a material emits light in response to the passage of an electric current or to a strong electric field.

• the result of radiative recombination of electrons and holes in a material, usually a semiconductor.

• the electron-hole recombination process produces some photons in the IR or visible.

• The junction in LED is forward biased.

Working…

• Consists of p-n junction diode dopped with Gan/InGaN• Current flows from p-side to n-side not in reverse• Charge carriers electrons and holes-flow into junction with different voltage• When electrons meet holes at junction• Then it falls into lower energy level and release energy in the form of light

• colour of LED based on band gap energy• Materials for led have direct band with energy corresponding to IR-UV region

• Advantages • Disadvantages

• Blue LEDs are environment friendly.

• Small, durable and need little power.

• Operate at a safe and low voltage

• Require less energy to provide light.

• A blue LED is necessary to make a white LED

• LEDs also last up to 100,000 hours, compared to 10,000 hours for fluorescent lights and 1,000 hours for incandescent bulbs.

• High life time –slow failure

• Very difficult to produce than other LEDs

• High initial price

• Blue hazard-can damage eye

• Blue pollution-cause light pollution

• Voltage sensitivity-should supply with the voltage above the threshold and a current below the rating

• Electrical polarity- only light with correct electrical polarity.

APPLICATION

• Used in flat screens and data storage.

• Used in accent Lighting fixtures

• It has been used to kill harmful bacteria that can cause dental and skin problems.

• Used to make white LEDs.

• Used in sterilization and hygiene.

• To help conducting studies of electro magnetic radiations.