Nonlinear optical crystals plays important role in the field of photo electronics, optical communication, optical modulators, laser spectroscopy, frequency conversion and so on. Semi-organic crystals exhibit high NLO response, thermal stability, laser damage threshold, mechanical stability, wide optical window transmittance and structural diversity. Combinations of inorganic and organic molecules yield the semi-organic crystals. Based on its structural diversity it’s classified into three categories. In this chapter explains various kinds of semi-organic crystals and their optical, thermal, mechanical, laser damage threshold value and NLO properties and also explains the importance of these crystals in the field of optoelectronics, frequency conversion and other optical applications.

Multicrystalline silicon solar cells occupy 62% in crystalline silicon solar cell production. It is grown by the directional solidification process. Solidification control has a vital role in directional solidification process. Cone shape groove is made in the directional solidification block to enhance the outgoing heat flux in the center region than the peripheral region. Five directional solidification furnaces are simulated for making a multicrystalline silicon ingot. First furnace is the conventional furnace, the second furnace has 30 mm × 85 mm groove block, the third furnace has 40 mm × 85 mm groove block, the fourth furnace has 50 mm × 85 mm groove block and the fifth furnace has 60 mm × 85 mm groove block. The von Mises stress in the maximum volume of the conventional and modified grown ingots are below the range of critical value. In conventional case 7% of the ingot volume is above critical stress value and in the modified cases 2.5% of the ingot volume is above critical stress value. If axial and radial temperature gradient is combined in the 50 mm × 85 mm groove block leads to better results.

The search and growth of nonlinear optical (NLO) crystals in the infrared (IR) area are significant and of high importance in the fields of NLO, signal communication, solid-state chemistry, and laser frequency conversion. Infrared NLO crystals have a wide IR transparent range, high laser damage threshold (LDT) value, and large NLO coefficients. This chapter presents the recent advances in IR-NLO crystals and especially emphasizes their crystal growth method, crystal structures, band gap value, LDT, and NLO properties. Based on its structural variety, it is categorized into chalcogenides, chalcohalides, oxides, halides, and oxyhalides. This chapter describes several kinds of IR-NLO crystals and their structural, band gap value, thermal, optical, LDT, and NLO properties and also describes the significance of these crystals in laser frequency conversion, optical parameter oscillator, and other optical applications.