What use are crystal field parameters? A chemist's viewpoint

Area of Science:

• Solid State Chemistry
• Quantum Chemistry
• Materials Science

Background:

• The crystal field model is the primary practical method for analyzing lanthanide ion (Ln(3+)) energy levels in crystalline hosts, achieving high accuracy.
• First principles methods are emerging but lack the current practicality of the crystal field model for this application.
• Accurate simulation of Ln(3+) energy levels is crucial for understanding their optical properties, including luminescence.

Purpose of the Study:

• To establish and validate three criteria for assessing crystal field parameters derived from Ln(3+) energy level data.
• To systematically analyze and simulate the energy level structures of the entire lanthanide series (except Pm(3+)) in Cs(2)NaLnCl(6) crystals.
• To provide accurate predictions of energy levels and identify potentially luminescent levels for Ln(3+) ions in hexachloroelpasolite hosts.

Main Methods:

• Crystal field parametrization of 4f(N) energy level data sets for Ln(3+) ions in Cs(2)NaLnCl(6) crystals.
• Systematic analysis of energy level data sets from Ln(3+) ions situated at high-symmetry sites.
• Application of a semiquantitative model to rationalize the variation of crystal field parameters based on 4f radial wave function distributions.

Main Results:

• The crystal field model, evaluated against three proposed criteria, demonstrated accurate fittings and predictive capabilities for Ln(3+) energy levels.
• Systematic and smooth variations in crystal field parameter values across the lanthanide series were identified and described by simple equations.
• Physical insights into crystal field parameter trends were gained, showing consistency with other host lattices like Cs(2)NaLnF(6).

Conclusions:

• The crystal field model provides a reliable and accurate method for simulating Ln(3+) energy level structures in crystalline environments.
• The established criteria effectively assess the quality of crystal field parametrization, guiding the selection and interpretation of parameters.
• The study successfully predicted energy levels and luminescent properties, offering valuable data for materials design and optical applications.