Gadolinium oxide host and europium/dysprosium/terbium doped gadolinium oxide nanoparticles were synthesized using the sonochemical technique. Gadolinium oxide nanocrystals were also co-doped with total 2 mol% of Eu(3+)/Dy(3+),Eu(3+)/Tb(3+),Dy(3+)/Tb(3+), and also Eu(3+)/Dy(3+)/Tb(3+) ions, by the same method. The nanoparticles obtained were characterized using powder x-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) techniques. The size of the particles ranged from 15 to 30 nm. The triple doped samples showed multicolor emission on single wavelength excitation. The photoluminescence results were correlated with the lifetime data to get an insight into the luminescence and energy transfer processes taking place in the system. On excitation at 247 nm, the novel nanocrystalline Gd(2)O(3):RE (RE = Dy, Tb) phosphor resulted in having very impressive CIE chromaticity coordinates of x = 0.315 and y = 0.316, and a correlated color temperature of 6508 K, which is very close to standard daylight.

Novel single, double and triple doped ZnAl2O4:M and ZnGa2O4:M (where M = Dy3+, Tb3+, Eu3+ and Mn2+) nanophosphors were synthesized through a simple sonochemical process and characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) spectrophotometry. The results of XRD and TEM show that resultant nanoparticles are single phase and have spherical shape. The doped samples showed multicolor emission on single wavelength excitation. Energy transfer was observed from host to the dopant ions. Characteristic blue and yellow emission from Dy3+ ions, green from Tb3+ ions and red from Eu3+ ions were observed. However, the Mn2+ ions in zinc gallate host yielded red emission which has been assigned to charge-transfer deexcitation associated with Mn2+ ion. The CIE coordinates of ZnGa2O4:Dy3+(2%):Tb3+(0.5%):Mn2+(2.5%) and ZnAl2O4:Dy3+(1.5%):Tb3+(0.25%):Eu3+(0.25%) nanophosphors are (0.304,0.310) and (0.312, 0.307), respectively, which lie in the white light region of the chromaticity diagram.

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The role of charge compensatory additives viz. monovalent ions (Li 1 , K 1 , and Na 1 ) codoped with Tb 31 in strontium silicate phosphors is investigated. The addition of charge compensators enhances the luminescence intensity of the prepared phosphors because they neutralize the charge generated by Tb 31 substitution for Sr 21 ions. The vacancy and defects created due to Tb 31 ions are suitably minimized by the addition of aliovalent impurities in the host. As the Tb 31 concentration is increased, the green emission surpasses the blue emission due to cross relaxation following the energy transfer process. The role of monovalent Li 1 ions among all charge compensator ions used was found to be most effective for enhanced Tb 31 ion emissions. As the Tb 31 concentration increases, the chromaticity coordinates shifts from the blue to green region and the correlated color temperature moves to the daylight region.

The application of lamp phosphors for accidental dosimetry is a new concept. Since the materials used in fluorescent lamps are good photo luminescent materials, if one can either use the inherent defects present in the phosphor or add suitable modifiers to induce thermoluminescence (TL) in these phosphors, then the device (fluorescent lamp) can be used as an accidental dosemeter. In continuation of our search for a suitable phosphor material, which can serve both as an efficient lamp phosphor and as a good radiation monitoring device, detailed examination has been carried out on cerium and terbium-doped lanthanum phosphate material. A (90)Sr beta source with 50 mCi strength (1.85 GBq) was used as the irradiation source for TL studies. The TL response as a function of dose received was examined for all phosphors used and it was observed that the intensity of the TL peak vs. dose received was a linear function in the dose range 0.1-200 Gy in each case. Incidentally LaPO(4): Ce,Tb is a component of the compact fluorescent lamp marketed recently as an energy bright light source. Besides having very good luminescence efficiency, good dosimetric properties of these phosphors render them useful for their use in accidental dosimetry also.

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