Describing a Real Source 1) Identify m of real source and adjust T in to line up m 2) The ratio of: 3) Measure T w ( ) to calculate  ( ) Ingle and Crouch, Spectrochemical Analysis

Nernst Glower Rare earth oxides formed into a cylinder (1-2 mm diameter, ~20mm long) Pass current to give: T = 1200 – 2200 K Can operate in air (no need for glass/quartz enclosure) Ingle and Crouch, Spectrochemical Analysis Douglas A. Skoog and James J. Leary, Principles of Instrumental Analysis, Saunders College Publishing, Fort Worth, 1992.

Globar Silicon Carbide Rod (5mm diameter, 50 mm long) Heated electrically to 1300 – 1500 K Positive temperature coefficient of resistance Electrical contact must be water cooled to prevent arcing Ingle and Crouch, Spectrochemical Analysis

Tungsten Filament Ingle and Crouch, Spectrochemical Analysis Heated to 2870 K in vacuum or inert gas Useful Range: 350 – 2500nm

Tungsten / Halogen Lamp I 2 or Br 2 added Reacts with gaseous W near the quartz wall to form WI 2 W is redeposited on the filament Gives longer lifetimes Allows higher temperatures (~3500 K) and thus higher apparent brightness

Arc Lamps Ingle and Crouch, Spectrochemical Analysis Electrical discharge is sustained through a gas or metal vapor Continuous emission due to rotational/vibrational energy levels and pressure broadening

H 2 or D 2 Arc Lamps Ingle and Crouch, Spectrochemical Analysis D 2 + E e-  D 2 *  D’ + D” + h D 2 + E e-  D 2 *  D’ + D” + h Energetics: E e- = E D 2 * = E D’ + E D” + h E e- = E D 2 * = E D’ + E D” + h Useful Range: 185 – 400 nm

Hg Arc Lamp Continuum + line source High power source Often used in photoluminescence Ingle and Crouch, Spectrochemical Analysis

Douglas A. Skoog and James J. Leary, Principles of Instrumental Analysis, Saunders College Publishing, Fort Worth, Hollow Cathode Discharge Tube Apply ~300 V across electrodes Ar + or Ne + travel toward the cathode If potential is high enough cations will sputter metal off the electrode Metal emits photons at characteristic atomic lines as the metal returns to the ground state

Hollow Cathode Discharge Tube Line widths are typically 0.01 – 0.02 Å FWHM Ingle and Crouch, Spectrochemical Analysis

Light-Emitting Diodes Operate with mW of power - ~80% efficiency Long lifetimes, stable output

Are you getting the concept? List one light source with each of the following characteristics. Common IR source: Spans UV – IR: Standard household/office lighting: Lights quickly to full brightness: Common atomic absorbance source: Common photoluminescence source: