Raman scattering (RS) and photoluminescence (PL) characterization of composition and residual strain have been presented in bulk mixed crystal system. RS and PL experiments were carried out on polycrystalline and crystalline bulk InxGa1-xAs as well as on crystalline bulk Si1-xGex materials. The shift in optical phonon in RS and electronic band gap energy in PL were found to be depended entirely on composition in polycrystalline materials, although they were changed by both composition and strain in crystalline materials having compositional variation. To confirm the above facts, chemical analysis (CA), energy dispersive X-ray (EDX), and optical transmission (OT) measurements were also performed, where CA and EDX measurements are not influenced by strain. Although RS and PL results showed good agreement with the CA results in polycrystalline materials, a large discrepancy was found among RS, PL, CA, OT, and EDX results due to the existence of strain in compositionally gradient crystalline InxGa1-xAs and Si1-xGex materials. By means of the strain models developed for the first time in bulk mixed crystal system, the quantitative amount of strain and its distribution have been analyzed and found to be highly sensitive to the compositional profile and its range. Further, the strain models in conjunction with RS, OT, and CA experiments have been applied for a simultaneous determination of composition and strain in crystalline Si1-xGex materials and the estimated results were in good agreement. Furthermore, both RS and PL results indicated that convection-induced local supercooling or constitutional supercooling could be the possible cause of polycrystallization in InxGa1-xAs crystal grown by the multi component zone melting method. In addition, compositionally homogeneous InxGa1-xAs crystals of about 3~5 mm in length and 10 mm in diameter were obtained from the preliminary growth experiments carried out by the traveling liquidus zone method.