Quantum physics got its start from the precise measurements of blackbody radiation, which forced physicists to face the failure of classical concepts (the Rayleigh-Jeans approach to applying simple electromagnetic concepts to thermal aspects): Planck introduced the concept of the quantum, in an act of conceptual desperation.
Subsequent development was forced by precise measurements of the frequencies and intensities of atomic emission lines, which set harder and harder problems for theoretical explanations to meet. The initial success of Bohr in understanding the hydrogen spectrum, and its extraordinary enhancement when faced with certain conceptual challenges (motion of the proton, relativistic considerations) could not be extended to multi-electron atoms without numerous complicated and ad-hoc inventions. The conceptual development of Quantum Mechanics had many contributors: Bohr, Kramers, Heisenberg, Born, Jordan, Dirac, Schrödinger, and others: It's still amazing to me how they developed these ideas. However, from the EXPERIMENTAL angle, the input was from precise measurement of emission lines.
It's interesting to note (looking at the Wikipedia article referenced below) that experiments important in the history of nuclear physics were going on during the same period. However, with the exception of Rutherford's earliest experiments on scattering of alpha particles (that gave him the key notion that the proper model for the atom was a tiny massive central positive nucleus surrounded by a cloud of light-weight electrons: This was the starting point for Bohr's model of the hydrogen atom), these did not contribute to the development of Quantum Mechanics.