The book highlights the potential use of rare earth ions in enhancing the properties of metal oxides. This book explores the effects of rare earth substitution on the structure and microstructure of metal oxides, exploring their multifunctional applications in energy harvesting, environmental sensing, and remediation. It presents significant improvements in material properties due to rare earth content, providing detailed methodologies for synthesis, advanced characterization techniques, and real-world application examples. The book addresses the growing interest in these materials by offering new research findings and revising foundational principles, making it a crucial guide for those looking to enhance their understanding and application of rare earth-doped nano-metal oxides in sustainable technology solutions. By bridging the knowledge gap, this book provides a unique focus on integrating rare earth elements into nano-metal oxides, showcasing their synergistic potential across energy, sensing, and environmental remediation fields. It offers practical examples and case studies that highlight the latest applications in real-world scenarios, particularly in the environmental and energy sectors. Contributions from interdisciplinary collaborations provides insights into novel methods and hybrid technologies that push the boundaries of current research. This book is an indispensable resource for material scientists, scholars, and researchers working in metal oxide nanomaterials by focusing on the latest advancements and practical applications.