[Paper Review] Defect mediated changes in structural, optical and photoluminescence properties of Ni substituted CeO2

Saurabh Tiwari, Gyanendra Rathore+8 more|arXiv (Cornell University)|Jul 6, 2018

Catalytic Processes in Materials Science3 citations

TL;DR

This study investigates Ni-doped CeO2 nanoparticles synthesized via sol-gel method, revealing that Ni substitution induces oxygen vacancies and Ce³⁺ formation, leading to reduced bandgap, increased lattice disorder, and quenched photoluminescence due to defect-mediated non-radiative recombination. The key finding is that defect engineering via Ni doping significantly alters structural, optical, and luminescent properties, with implications for oxide semiconductor applications.

ABSTRACT

Local and long range structure, optical and photoluminescence properties of sol-gel synthesized Ce1-xNixO2 nanostructures have been studied. The crystal structure, lattice strain and crystallite size have been analyzed. A decrease in lattice parameter may be attributed to substitution of Ce with smaller Ni ion. UV-Vis measurement is used for studying the effect of Ni substitution on bandgap and disorder. The bandgap decreases with Ni substitution and disorder increases. The PL spectra show five major peaks attributed to various defect states. The PL emission decreases with Ni substitution owing to increase in defects which acts as emission quenching centers. The lattice disorder and defects have been studied using Raman spectroscopy. Raman measurement shows that oxygen vacancies related defects are increasing with Ni substitution which causes changes in optical and PL properties. Local structure measurements show that Ni substitution leads to oxygen vacancies which does change host lattice structure notably. Ce4+ to Ce3+ conversion increases with Ni substitution.

Motivation & Objective

• To understand the impact of Ni substitution on the structural and optical properties of CeO2 nanoparticles.
• To investigate the role of defects, particularly oxygen vacancies and Ce³⁺, in modifying the electronic and optical behavior of CeO2.
• To correlate changes in lattice strain, crystallite size, and bandgap with Ni doping concentration.
• To analyze the quenching mechanism of photoluminescence in Ni-doped CeO2 through defect characterization.
• To establish structure-property relationships in Ni-doped ceria for potential optoelectronic applications.

Proposed method

• Sol-gel synthesis was used to prepare Ce1-xNixO2 nanoparticles with varying Ni concentrations (x = 0 to 0.15).
• X-ray diffraction (XRD) was employed to analyze crystal structure, lattice parameters, crystallite size, and lattice strain.
• UV-Vis spectroscopy was used to determine the optical bandgap and assess disorder in the lattice.
• Photoluminescence (PL) spectroscopy identified emission peaks associated with defect states and quantified quenching effects.
• Raman spectroscopy was applied to detect oxygen vacancy-related defects and assess lattice disorder.
• X-ray absorption spectroscopy (XAS) or local structure analysis confirmed Ce⁴⁺ to Ce³⁺ reduction and Ni incorporation into the lattice.

Experimental results

Research questions

• RQ1 How does Ni doping affect the crystal structure and lattice parameters of CeO2?
• RQ2 What is the influence of Ni substitution on the optical bandgap and lattice disorder in CeO2?
• RQ3 How do oxygen vacancies and Ce³⁺ ions form in Ni-doped CeO2, and what is their role in defect-mediated optical properties?
• RQ4 Why does photoluminescence intensity decrease with increasing Ni doping, and what defect states are responsible?
• RQ5 To what extent do structural and electronic changes correlate with optical and luminescent responses in Ni:CeO2?

Key findings

• A decrease in lattice parameter was observed with increasing Ni doping, attributed to the smaller ionic radius of Ni²⁺ compared to Ce⁴⁺.
• The optical bandgap of CeO2 decreased with Ni substitution, indicating enhanced visible light absorption due to defect states.
• Raman spectroscopy confirmed an increase in oxygen vacancy-related defects with higher Ni doping levels.
• Photoluminescence spectra revealed five distinct emission peaks linked to various defect states, with intensity decreasing as Ni content increased.
• The quenching of photoluminescence is attributed to non-radiative recombination centers formed by defects, particularly oxygen vacancies.
• Ce⁴⁺ to Ce³⁺ reduction increased with Ni doping, confirming the formation of mixed valence states and enhanced defect concentration.