  We study the evolution of the dynamical spin structure factor in a spin-1
antiferromagnetic Heisenberg chain which is randomly doped with spin-1/2
moments. Using stochastic series expansion Quantum Monte Carlo simulations
combined with the Maximum Entropy method, we monitor the crossover from the
spin-1 chain, dominated by a single resonance at the Haldane energy, to the
spin-1/2 chain with a continuum of spinon states which diverges at
zero-frequency. Upon increasing the doping level, spectral weight is rapidly
transferred from the Haldane peak to lower energies. If the exchange couplings
between the spin-1/2 substituents and the spin-1 sites of the host are
sufficiently small, finite-frequency bound states are observed below the spin
gap for small doping concentrations.
