High refractive index and transparent heavy metal oxide glassy thin films

Heavy metal oxide thin films of the ternary system Nb2O5-GeO2-PbO have been prepared by pulsed laser deposition in an O-2 environment from either glassy or crystalline bulk samples. The range of ([Pb] + [Nb]) content in which the films are optically homogeneous and transparent is much broader (0.5-1.0) than that of the bulk samples considered in the present work (0.55-0.62). The imaginary part of the refractive index is very low in all cases (k < 10(-3)), whereas the real part increases linearly with the ([Pb] + [Nb]) content up to values as high as 2.35. The optical energy gap has been found to be strongly dependent on [Pb], whereas it is almost independent of [Nb]. This dependence is discussed in terms of the role of Pb and Nb as network modifiers or formers.