Optically active spin defects in diamond, often named color centers, are prime candidates for quantumtechnologies, including quantum networking, computing, sensing, and photonics. Integrating single-crystal diamond with heterogeneous materials unlocks numerous research directions that are non-trivial for bulk diamond or nanodiamond. This thesis describes a deterministic method for diamond membrane synthesis and integration to expand integration options for hosted color centers. This heterogeneous material platform enables efficient spin-photon interfaces and improves the coherence of color centers, two key elements of quantum networking. The platform also offers a versatile and practical interface for quantum sensing and provides an opportunity to explore atomic-scale optical interaction in solids. Chapter 1 introduces the fundamentals of quantum technology, diamond color centers for quantum applications, and material properties of diamond with synthesis methods. Chapter 2 provides the research background of low-dimensional diamond fabrication and details our approaches to generating high-quality diamond films and integrating them with a wide selection of materials. Chapter 3 demonstrates multiple fabrication methods of nanophotonic cavities with diamond-based heterostructures and their coupling to color centers. Chapter 4 presents our work on strain generation in thin-film diamonds and modification of the spin dynamics for tin-vacancy centers using strain. Chapter 5 discusses the spin coherence of nitrogen-vacancy centers in diamond membranes and their applications for quantum bio-sensing. Chapter 6 describes our study on near-field enhancement of germanium-vacancy centers based on the behavior of nearby carbon vacancies. Chapter 7 concludes the thesis and provides an outlook on this platform in quantum technologies.