Fluorescent lamp: who emits UV?

[giuliopascal]

Hi everyone,

searching on the web about how the fluorescent lamps work, I cannot understand if the UV is emitted by the noble gas or the mercury.
For what I understand, both of them ionize, and the UV light is emitted after the collision of the electrons with the atoms, but I would like to know something more about this process and the specific role of argon and mercury.

Thank you very much!

 

[Dr. Courtney]

There are three emission mechanisms in play: atomic emission from spectral lines, thermal emission of matter at a given temperature, and emission from charged particles when they undergo acceleration.

Atomic emission from spectral lines can be traced to specific atomic species. Thermal emission can be traced if the sources have different temperatures, but the temperature of the gases in the tube are not high enough for UV. Emission from charged particles is harder to trace. A thermal or electrical plasma will simply emit radiation related to its charged particles acclerating and colliding. I don't think one can conclude that one charged particle plays a much larger role than the others.

 

[Andy Resnick]

Hi everyone,

searching on the web about how the fluorescent lamps work, I cannot understand if the UV is emitted by the noble gas or the mercury.
For what I understand, both of them ionize, and the UV light is emitted after the collision of the electrons with the atoms, but I would like to know something more about this process and the specific role of argon and mercury.

Thank you very much!

Typical fluorescent bulbs are essentially low-pressure mercury arc lamps. There is a lot of heavy-duty physics involved, but basically the Hg is first vaporized and then ionized. When the Hg ion recombines with an electron, light is emitted. The argon is a 'buffer gas' and is only there to assist the initial vaporization of Hg.

http://www.lamptech.co.uk/Documents/M1 Introduction.htm

The dominant UV emission lines for these bulbs are at 253 and 365 nm:

http://physics.nist.gov/PhysRefData/Handbook/Tables/mercurytable3.htm#1849.499

Germicidal bulbs use the 253 nm line to sterilize.

 

[giuliopascal]

Thank you very much. Now I understand a little more