ELECTRONIC SPECTRAL STUDIES ON RARE-EARTH-DOPED PSEUDOGARNETS

Spectral parameters viz. oscillator strengths (P), Judd-Ofelt paramete rs (tau(lambda)), inter-electronic repulsion (Racah) delta E(k) parame ters (IERP) and nephelauxetic ratio (delta E(3)/delta E(1)) have been determined using aqueous solutions of representative lanthanide (rare earth) (III) ions, Pr(III), Nd(III), Sm(III), Eu(III), and Er(III) and rare earth-doped concentrated (similar to 1.0 M) solutions of pseudog arnets sodium m-silicate, sodium molybdate and sodium m-vanadate. Thes e parameters have been studied as a function of (i) symmetry around th e Ln(III) ions, and (ii) matrix environment due to different pseudogar nets. The electronic transitions for various Ln(III) ions and changes in their positions due to corresponding changes in matrix environment are observed to show red shift. The oscillator strength values increas e significantly in the sequence aqua < MoO42- < VO3- < SiO32-. The tau (lambda) values are found to lie in the order tau(6) > tau(4) > tau(2) . The delta E(k) and delta E(3)/delta E(1) values are observed to lie in the theoretically calculated ranges. The nature of dopant-matrix in teraction appears to change from ionic to ionocovalent on going across the Ln(III) series.