Chemicals Based
Technologies - 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
