Fluorescent Lamp Phosphors

The fluorescent lamp is basically a low pressure mercury discharge lamp with a layer of phosphor particles on the inside surface of the glass tube, as shown in 6.6.6., presented on the next page. 

The lamp has an internal gas-fill pressure of about 1 -2 mm pressure and contains a mixture of Ne, A, and Kr gases. The internal radiation generated is mostly (85%) 2537 A, which is the resonamce wavelength of the mercury vapor discharge. The other 15% is distributed between 1850 A, 3150 A, 3650 A, 4300 A, 5460 A, and 5785 A. The general phosphor system used has the apatite structure with the general composition  

Typical lamp phosphors are shown in the following table  

There are a number of specialty phosphors that have been used to mcike LPMV lamps for special purposes. These are listed in Table 6-5  

These phosphors are used primarily in Black-Light lamps and photocopy machines such as those marketed by Xerox Corp. 

---

In fluorescent lamps, phosphors are coated on the inside of the lamp tube using a slurry containing the powder and a Hquid which is either poured down through the tube, up-flushed, or in some cases the tubes are filled and then drained. Because of concerns over having volatile organic solvents in the air, the hquid medium containing the powder is usually water with an added agent, a thickener, to increase the viscosity of the suspension, such as poly(methacryhc... 

K. H. Butler Fluorescent Lamp Phosphors. The Pennsylvania State University Press, London 980. 

Reduction processes are frequently involved in doping of materials prepared for specific applications. Bai <5Sr(5MgF4 (< < 0.55) was doped with Sm2+ by addition of Sm metal to the charge for crystal growth [48], Eu2+ is the key ion in fluorescent lamp phosphors for emission of blue light. Respective reduction of Eu3+ is frequently achieved in H2 atmosphere, but in alkaline earth fluoride phosphates, Sn2+ may act as reducing agent [49]. 

Device Cathode-ray tube Plasma display panel Fluorescent lamp Phosphor-converted LED lamp... 

Srivastava AM, Sommerer TJ. Fluorescent lamp phosphors. Electrochem Soc Interface 1998 28-31. 

Butler, K. H. Fluorescent Lamp Phosphors, Technology and Theory, Philadelphia, Pennsylvania State University Press 1980... 

SYNTHETIC APATITE USE IN FLUORESCENT LAMPS AND LASERS Fluorescent lamp phosphors... 

Figure 7.55 Comparison of commercial fluorescent lamp phosphors, showing clear differences in the chemical composition of the materials. The sample powders required no sample preparation prior to analysis.

K.H. Butler, Fluorescent Lamp Phosphors, University Press, 1986. 

Butler K (1980) Fluorescent lamp phosphors. Pennsylvania State University Press, UnivCTsity Park, p 117... 

Nonradiative Decay. To have technical importance, a luminescent material should have a high efficiency for conversion of the excitation to visible light. Photoluminescent phosphors for use in fluorescent lamps usually have a quantum efficiency of greater than 0.75. AH the exciting quanta would be reemitted as visible light if there were no nonradiative losses. 

The Calcium Halophosphate Phosphors. Early fluorescent lamps used various combinations of naturally occurring fluorescent minerals. The development of the calcium halophosphate phosphor, Ca (P0 2(Cl, F) Sb ", Mn, in the 1940s was a significant breakthrough in fluorescent lighting (7). As is often the case in new phosphor discoveries, this phosphor was found accidentally while searching for phosphors for radar screens. 

Because it is stiU by far the most commonly used phosphor in fluorescent lamps, calcium halophosphate total production far exceeds that of all other phosphors put together, in excess of 1000 metric tons per year. 

The cost of rare-earth phosphors in fluorescent lamps is often reduced by double coating the lamps. The rare-earth phosphor blend is coated over a base layer of the inexpensive halophosphate phosphor (Fig. 9). In this configuration it absorbs a disproportionate amount of the uv discharge. For example, about 70% of the uv is absorbed in the inner coating with only one layer of triphosphor particles on the inside. 

Fig. 9. A modem fluorescent lamp coating including a conductive layer of Sn02 F, then a protective coating of finely divided alumina, followed by the inexpensive halophosphate phosphor, and finally a thin layer of the triphosphor rare-earth blend.

Donor and acceptor levels are the active centers in most phosphors, as in zinc sulfide [1314-98-3] ZnS, containing an activator such as Cu and various co-activators. Phosphors are coated onto the inside of fluorescent lamps to convert the intense ultraviolet and blue from the mercury emissions into lower energy light to provide a color balance closer to daylight as in Figure 11. Phosphors can also be stimulated directly by electricity as in the Destriau effect in electroluminescent panels and by an electron beam as in the cathodoluminescence used in television and cathode ray display tubes and in (usually blue) vacuum-fluorescence alphanumeric displays. 

Phosphors are inorganic materials which convert incident radiant energy to visible light within a device. The device chosen can be a cathode-ray tube, i.e.- a television tube, or a fluorescent lamp. A phosphor consists of a matrix modified by an additive chosen so that it becomes optically active within the matrix, or compound. This is an example of a substitutional impurity in a lattice wherein the additive, usualty Ccdled an "activator", introduces a lattice defect that is optically active. However, the added impurity still follows all of the rules found for defects in a lattice, as shown by the following example. 

---