# Defect Tolerant Quantum Cutting in Mechanosynthesized Ytterbium-Doped Cesium Lead Chloride Perovskites

## TL;DR

This paper explores how doping cesium lead chloride perovskites with ytterbium can enhance photoluminescence, even with defects, using mechanosynthesis and NMR.

## Contribution

The study identifies conditions for optimal quantum cutting in doped perovskites through mechanosynthesis and NMR analysis.

## Key findings

- Higher ytterbium doping correlates with shorter NMR relaxation times due to paramagnetic effects.
- Excess lead and chloride ions favor defect incorporation that enhances photoluminescent quantum yields.
- Optimal PLQY occurs at 5% doping after 1-2 hours of grinding, with further grinding reducing performance.

## Abstract

Ytterbium doped cesium lead halide materials exhibit
a property
known as quantum cutting which allows for greater than 100% photoluminescent
quantum yields (PLQYs). The local atomic structure of the defects
responsible for these properties and the effectiveness of the doping
for producing the desired PLQYs is not readily discerned using techniques
requiring long-range order. In this work we prepared 2.5, 5, 10, and
20% Yb3+ doped CsPbCl3 powders using mechanosynthesis
under distinct stoichiometric ratio conditions and characterized the
defect incorporation and its effects on local atomic disorder using
solid-state nuclear magnetic resonance (SSNMR) spectroscopy. We then
correlate our observations to the observed PLQYs for each of the prepared
samples. All samples prepared were found to be in an orthorhombic
phase and no lattice shrinking was observed upon increased Yb3+ doping. An increase in doping concentrations was accompanied
by a decrease in 133Cs NMR spin–lattice relaxation
times T
1 consistent with a paramagnetic
relaxation enhancement effect induced by Yb3+ incorporation
into the perovskite lattice. Through a comparison of synthesis methods,
PLQY and NMR T
1 parameters we found that
incorporated defects favorable for PLQY in mechanosynthesized samples
are more likely to form in the presence of excess lead and excess
chloride ions. The maximum PLQY values obtained for each set of samples
correlated with T
1 parameters in the range
of 13 to 35 s. In addition, we found that the observed PLQY in 5%
doped samples was optimized after 1 to 2 h of interval grinding in
stainless steel jars. Further grinding beyond 2 h led to a reduction
in particle size below 1 μm as well as a reduction in PLQY and
spin relaxation times.