Index of Refraction for Nano-Ceramic Materials
|Artur Bednarkiewicz , Piotr Mazur , Dariusz Hreniak , Wiesław Stręk|
Polish Academy of Sciences, Institute of Low Temperature and Structure Research (INTiBS), Okólna 2, Wrocław 50-422, Poland
The index of refraction for Nd3+ and Eu3+ doped Y3Al5O12 ceramics was measured and compared with that of bulk material. The Sellmeier equation n2(λ[μm])=A+Bλ2/(λ2-C) was found to have A, B and C equal to 1, 1.44156, 0.06716 and 1, 1.36429, 0.05849 for Nd:YAG and Eu:YAG respectively, in comparison to single Nd:YAG crystal 1, 2.2779 and 0.01142. At 614nm where Eu3+:5D0-->7F2 appears the index of refraction for ceramics is n=1.617 whereas for YAG single crystal it is n=1.830. At 909nm where Nd3+:4F3/2-->4I9/2 appears the index of refraction for ceramics is n=1.604 whereas for single YAG crystal it is n=1.819.
The Einstein’s coefficient Ai for electric-dipole transitions depends on index of refraction according to χABSED = (n2+2)2 / 9n and according to χEMIED = n(n2+2)2 / 9 for absorption and emission respectively. Thus one may expect the absorption coefficient to be reduced in nanocrystals based materials in comparison to bulk one. The lower index of refraction measured for ceramics, should reduce the absorption coefficient down to ~84% of the value for both Nd3+ and Eu3+ doped YAG single crystal. One may also expect the lifetimes to be longer in nanocrystals based materials in comparison to bulk one. The measured indexes of refraction for Eu3+ or Nd3+ doped ceramics reduces the χED for luminescence down to ~66% of the value for YAG single crystal and may lead to 1.5 times increased decay constants. These effects could be one of explanations of the long lifetimes observed by us in Nd3+ and Eu3+ doped nanopowders. The measured lifetimes for 0.5 and 1%Nd:YAG nanopowders exceeded 400μs (485 and 420μs respectively), however for the ceramics the lifetimes decreased down to 230 and 210 μs respectively. We thus suppose the reabsorption of radiation could also play a role in highly scattering medium like powders.
Presentation: poster at E-MRS Fall Meeting 2005, Laser Ceramic Symposium, by Artur Bednarkiewicz
See On-line Journal of E-MRS Fall Meeting 2005
Submitted: 2005-05-24 13:06 Revised: 2009-06-07 00:44