Production of Yttrium Vandate Phosphor

Introduction

Rare earth phosphors find commercial application in the lamp industry. Mercury fluorescent lamps, of late have become synonymous with the red emitting europium activated phosphors because of its excellent colour correcting and energy converting properties. Nearly 50% of the emitted radiant power in a high pressure mercury vapour lamp (HPMV) is in the ultraviolet region. This power if untrapped and unutilised is not only wasteful but also harmful for the normal human vision. Moreover, since the mercury discharge is deficient in the red region of the visible spectrum, the objects under illumination evoke a colour sensation which is distinctly different from that due to natural daylight. The inside of a lamp envelope coated with an europium activated rare earth phosphor traps this invisible energy, shapes it and re-emits in the form of pure red colour, thus enriching the emitted light of the mercury lamp with a degree of natural daylight colour rendition. In addition, it also acts as a source of energy converter from invisible ultraviolet to visible light.

Characteristic features of a rare earth phosphor for mercury vapour lamp applications are:

• Narrow band red spectral emission which matches exactly with the eye response of the red spectral receptor in the eye, leading to high luminous efficiency.
• High quantum efficiency of near 100% i.e., the emission of a visible quantum of light for every ultraviolet photon of energy it absorbs.
• The phosphor does not absorb its own emission.
• Makes the lamp compact, efficient in energy and in colour rendition.

Synthesis of YVO4: Eu phosphor, which is currently being imported by the lamp manufacturers in the country, has been established. This phosphor has been tested for 400 watts HPMV lamps and performance found to be at par with that of the imported ones.

For further information please contact :

Head,
Technology Transfer & Collaboration Division,
Bhabha Atomic Research Centre, Trombay,
Mumbai - 400 085
Tel : 091-022-25505337/25593897
Fax : 091-022-25505151
E-mail : headttcd@barc.gov.in