A spectroscopic and structural study on a series of pure and mixed lanthanide orthophosphates

Structural and spectroscopic analyses on a series of lanthanide orthophosphates in both pure and mixed forms were performed in order to measure symmetry and crystal-field effects on the lanthanide ions in different environments. Judd-Ofelt intensity parameters were calculated in order to monitor the various phenomenological effects of the Ln{dollar}sp{lcub}3+{rcub}{dollar} ions in monoclinic and tetragonal hosts. The behavior of the Judd-Ofelt parameters, {dollar}taulambda{dollar}, (where {dollar}lambda{dollar} = 2, 4, and 6) with change in symmetries and ion-ion interactions is of particular interest. Based on assigned energy levels, interactions between the host and dopant ions in mixed systems were monitored by shifts and broadening of spectral bands of the individual ions as compared to that observed for the pure form. Hypersensitivity was largely quenched in the tetragonal hosts as expected due to their higher symmetry. Also, shifts in the transition energy levels were observed to occur for the host and dopant ions. Changes in transition manifold splittings result mainly from symmetry changes between the C{dollar}sb{lcub}rm s{rcub}{dollar} symmetry of the nine-coordinated monoclinic host and the D{dollar}sb{lcub}rm 2d{rcub}{dollar} symmetry of the eight-coordinated square antiprism (SQAP) geometry of the tetragonal form. The broadening of certain bands and the degree of splitting within transition manifolds indicate that strong interaction occurs between the mixed ions, especially in the case of Nd{dollar}sp{lcub}3+{rcub}{dollar} in ErPO{dollar}sb4{dollar}. The various modes by which optical transitions occur in these crystalline systems are addressed along with the calculation of transition oscillator strengths. A discussion of experimental methods and comparison of results obtained for the respective ions in other forms is also given. Interpretation of these results is made based on ion-ion interactions and structural effects.