Energy-Level Scheme for Np4+ in PbMoO4

Abstract

Neptunium‐doped (Na‐charge‐compensated) crystals of PbMoO₄ were grown by the Czochralski method. The absorption spectrum between 5000 and 25 000 cm⁻¹ was obtained on a Cary‐14 spectrophotometer. The fluorescent spectrum between 4000 and 7000 cm⁻¹ was obtained on a specially modified Beckman DK‐2 spectrophotometer. The free‐ion parameters obtained from a least‐squares fit to the five lowest free‐ion levels neglecting configuration mixing are $E^1\text{\hspace{0.17em}=\hspace{0.17em}2970.0}{\mathrm{cm}}^{\text{−1}}{\mathrm{,\; E}}^2\text{\hspace{0.17em}=\hspace{0.17em}14.01}{\mathrm{cm}}^{\text{−1}}{\mathrm{,\; E}}^3\text{\hspace{0.17em}=\hspace{0.17em}312.1}{\mathrm{cm}}^{\text{−1}},\mathrm{and}{\xi }_{\text{5f}}\text{\hspace{0.17em}=\hspace{0.17em}2.89.2}{\mathrm{cm}}^{\text{−1}}$ . The rms deviation for this fit was 17 cm⁻¹. A first‐order crystal‐field perturbation calculation was carried out. A least‐squares fit to the 10 lowest Stark levels yielded the following values for the crystal‐field parameters: $B_0^2\text{\hspace{0.17em}=\hspace{0.17em}2580.7}{\mathrm{cm}}^{\text{−1}}{\mathrm{;\; B}}_0^4\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}3534.0}{\mathrm{cm}}^{\text{−1}}{\mathrm{;\; B}}_0^6\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}1476.6}{\mathrm{cm}}^{\text{−1}}{\mathrm{;\; B}}_4^4\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}2892.5}{\mathrm{cm}}^{\text{−1}}{\mathrm{;\; B\prime }}_4^4\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}918.6}{\mathrm{cm}}^{\text{−1}}{\mathrm{;\; B}}_4^6\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}663.9}{\mathrm{cm}}^{\text{−1}},\mathrm{and}{\mathrm{B\prime }}_4^6\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}211.4}{\mathrm{cm}}^{\text{−1}}$ with an rms deviation of 40 cm⁻¹. A similar least‐squares fit, including the effects of $\mathrm{J–J}$ mixing, could not be carried out due to rather large computation time requirements. However, it was found that for the lowest state $\text{[J\hspace{0.17em}=\hspace{0.17em}9/2(I)]}$ , the mixing effects are less than 30 cm⁻¹ whereas for the first excited state $\text{[J\hspace{0.17em}=\hspace{0.17em}11/2(I)], J–J}$ mixing can shift levels by as much as 80 cm⁻¹. The results for Np⁴⁺ are compared with those for the “isoelectronic” ion Nd³⁺.