Charge carrier mobility and nonproportionality of LaBr$_3$:Ce scintillators

TL;DR

This study investigates how charge carrier mobility influences the nonproportional response and energy resolution of LaBr3:Ce scintillators across a temperature range, linking microscopic transport properties to macroscopic scintillation performance.

Contribution

It provides a detailed analysis of charge carrier mobility's role in scintillator nonproportionality, supported by experimental data and theoretical modeling of carrier transport in LaBr3:Ce.

Findings

Optimal temperature for proportionality varies with Ce concentration.

Carrier scattering by lattice and impurities affects mobility and nonproportionality.

Maximum mobility correlates with minimum nonproportional response.

Abstract

The nonproportional response and related energy resolution of LaBr$_3$:Ce$^3+$ scintillation crystals doped with different concentrations of cerium were studied between 80K and 450K. For Ce$^3+$ concentration of 5% and 30%, LaBr$_3$ showed best proportionality and energy resolution at 80K. For LaBr$_3$:0.2%Ce$^3+$ the best energy resolution and the lowest degree of nonproportional response were instead observed around room temperature. The experimental results were analyzed in terms of charge carrier mobility and using theory of carrier transport in wide band gap semiconductors. We found that scattering of carriers by both lattice and impurity are the key processes determining the particular temperature dependence of carrier mobility and ultimately the scintillation nonproportionality. The calculated maximum of the LaBr$_3$:0.2%Ce$^3+$ carrier mobility corresponds well with the experimentally observed minima of its degree of nonproportionality, when assuming about 100ppm ionized impurity concentration.