<p>The spectral mismatch between solar cells and incident radiation fundamentally limits their efficiencies as photons outside the optimal absorption range of the cell are lost due to transmission or thermalization. This challenge has driven research into materials and processes capable of modifying the solar spectrum to align better with the absorption characteristics of photovoltaic devices. Rare-earth-doped glasses and glass ceramics have emerged as promising candidates for addressing this limitation, exploiting energy up-conversion and down-conversion mechanisms to enhance solar cell performance. This review provides a systematic comparison of rare-earth-doped glasses, nanoparticle-embedded glass ceramics and transparent glass ceramics as spectral modification materials for photovoltaic applications, with emphasis on their underlying energy conversion mechanism. Alternative emerging approaches such as perovskite quantum dot-embedded glasses and organic luminophores are reviewed to provide a broader perspective on spectral conversion technologies. Device-level challenges and future opportunities are also discussed. It is observed that rare-earth-doped materials offer a transformative approach to overcoming the spectral mismatch problem, paving the way for more efficient and sustainable solar energy technologies.</p>