Doping phosphor

It was found that that in the case of soft beta and X-ray radiation the IPs behave as an ideal gas counter with the 100% absorption efficiency if they are exposed in the middle of exposure range ( 10 to 10 photons/ pixel area) and that the relative uncertainty in measured intensity is determined primarily by the quantum fluctuations of the incident radiation (1). The thermal neutron absorption efficiency of the present available Gd doped IP-Neutron Detectors (IP-NDs) was found to be 53% and 69%, depending on the thicknes of the doped phosphor layer ( 85pm and 135 pm respectively). No substantial deviation in the IP response with the spatial variation over the surface of the IP was found, when irradiated by the homogeneous field of X-rays or neutrons and deviations were dominated by the incident radiation statistics (1). 

Moine B, Bizarri G. Rare-earth doped phosphors oldies or goldies Mater Sci Eng B 2003 105 2-7. 

The TL peaks at about 415 K in (a), (b) and (c) may be of some interest in dosimetry. These peaks become dominant at higher doses. In the case of CsCkEu the authors show its linear dose response and conclude that it may suit for radiation dosimetry. In (b) and (c) the dose response is sublinear. This conclusion seems however to have resulted from overlap with other peaks. Proper resolution of the peaks by prewarming to a temperature close to 400 K or by total-glow-curve computer fitting may show linear dose dependence also for the Sm- and Tb-doped phosphors. 

Strontium fluorohalide hosts doped with Yb or Eu were studied by Schipper and Blasse (1991). The paper deals mainly with the PL of Yb-doped SrFBr and SrFCl. The phosphors were prepared by keeping the mixture of chemicals at 980°C for seven days. For the TL measurements the samples were X-irradiated at RT and heated at 10"Cmin". The main TL appeared at 320-340 K, with weaker peaks up to about 480 K. The Eu doping gave a TL sensitivity nearly 3 times that of Yb. The weak TL of the Yb-doped samples is not surprising and fits qualitatively the results for CaS04 Yb (see fig. 29). The authors stress the similarity of the glow curves of the Yb- and Eu-doped phosphors and conclude that the excitation and TL emission mechanisms are the same for both phosphors. 

Studies of lanthanide complexes under such multiphoton excitation are rare [24, 76-78], and further work is necessary to identify complexes that have a suitable response towards multiphoton excitation under biological conditions. We note that multiphoton-excited luminescence, which involves the simultaneous absorption of several photons, is different from the upconversion luminescence for lanthanide-doped phosphors described earlier in this chapter, which is based on the sequential absorption of photons. 

PLE spectrum monitoring the orange band of Mn " reflects the characteristics of in the codoped material, thus demonstrating effective energy transfer from Eu (D) to Mn " (A). The PLE spectrum covers the spectral region of 225-425 nm, thus implying that the doubly doped phosphor is suitable to near-UV LED excitation. 

The demand for efficient WLED phosphors stimulated investigations of new Eu -doped phosphors, e.g., oxynitrides, nitrides, aluminates, and aluminosilicates. Among these, nitrides and oxynitrides have been the subjects of intensive stodies because of their outstanding performances such as quantum yield >80 %, and high thermal and chemical stability [6-8, 22, 24—27]. However, the synthesis of these hosts must be performed at high temperature and high pressure, e.g., 1900 °C and 10 atm N2 atmosphere for Eu -doped -SiAlON [24]. The harsh preparation conditions and high price of raw materials destine these phosphors to be costly. 

Eu Eu -" is a typical and efficient activator for red-emitting phosphor due to its transitions from the excited Dq level to the Fj (J = 0-4) levels of the 4/ configuration. Its photoluminescence emission strongly depends on the symmetry of the crystal stmcture of Eu " occupied site in the host. The optical transitions of Eu " ions originating from the electronic dipole and magnetic dipole interaction of the internal 4/electrons are deeply affected by the crystal environment. If the Eu " ions occupy the sites with inversion symmetry, the emission will peak at 590-600 nm from the Dq Fi magnetic-dipole transition. This will dominate the emission, which is not affected much by the site symmetry. In contrast, the emission peaks at approximately 610-630 nm, due to the Dq p2 electronic dipole transition, will dominate the emission if the Eu " ion substitutes the site with no inversion symmetry [56], Moreover, Eu -doped phosphors usually have intense intrinsic... 

Until now, downconversion based on the four concepts mentioned previously has been demonstrated. The first example was demonstrated in single Pr -doped phosphor. In this case, it requires the So level of Pr to be located below its lowest AfSd state. When Pr is pumped to its Sq level, two-photon emission is completed by two subsequent emissions of 405 nm for the Sq transition followed by radiation of 480 nm for the Pq H4 transition or of 610 nm for the Pq transition as shown Fig. 16.8. Until now, cascade emission from Pr has been found in a number of fluoride hosts [11-20] such as SrAlFs [11, 12], LnF(Ln = Y, La, Lu) [13-16], BaMgp4 [15], AYp4(A = Na, K) [13, 17], AMgF3(A = Na, K) [18, 19], and LiSrAIFe [20]. Figure 16.9 shows the emission spectrum of single... 

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