CHEM01200604004 Shri Sanyasinaidu Boddu - Homi Bhabha ...

decay-time reduction is much easier to measure than the reduction in the quantum efficiency.
The critical concentration is that for which the lifetime starts to be reduced.
For employing lanthanide luminescence for various applications, two approaches, are
followed. They are (i) in the form of lanthanide doped bulk inorganic materials and (ii) in the
form of lanthanide complexes. In the former case, their luminescence efficiency is very high,
they are chemically stable but their processability is very poor. In the latter case, their
processability is very good but their luminescence efficiency and chemical stability is poor. If
one dopes lanthanide ions in processable inorganic nanoparticles then they can have
advantages of both inorganic bulk materials and complex compounds. Because lanthanide
ions will be inside the robust inorganic particle which will give the good luminescence
efficiency and the surface of the nanoparticles will be functionalised with ligand molecules
which will give good processability. As a result, they can be dispersible in polar/ nonpolar
solvents and they can be incorporated in inorganic polymers like silica, alumina or organic
polymers like PMMA, PVA, etc. Reduced scattering and homogeneous composite formation
capability with polymers make the nanoparticles as better candidates for luminescence
applications.
1.6 Recent work on luminescent nanomaterials: The luminescent nanomaterials can be
broadly classified into two categories. In the fist category of nanomaterials luminescence is
arsing due to the inherent nature of the material or the type of structural units present in the
material, whereas in the second category, luminescence is attributed to the dopant ion present
in the non-luminescent host having nano size dimensions. Oxides like ZrO 2 , Ga 2 O 3 , SnO 2 ,
ZnO, Sb 2 O 3 , ZnGa 2 O 4 , BaSnO 3 , etc. are examples of the first category of materials. Systems
like Y 2 O 3 :Ln, Y 3 Al 5 O 12 :Ln, YPO 4 :Ln, CePO 4 :Ln, LaF 3 :Ln, GdF 3 :Ln, etc. (where Ln stands
for the lanthanide ion) are few examples of second category of materials. Some of the
transition metal ions also act as luminescent centers in different inorganic hosts. In the
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