The reported value of the optical transparency for KDP is from 190 to 1500nm [24]. The UV–vis spectra recorded for pure and different molar ratios of K2CO3-added KDP crystals is shown in Fig. 5. It is clear from the figure that the crystal has sufficient transmission in the entire visible and IR region. The optical transparency of the KDP crystal is increased by the addition of 5M% K2CO3 additive. It has also been observed that the cutoff wavelength is almost the same for pure and additive-added KDP crystals. The addition of the dopant K2CO3 in the optimum conditions to the solution is found to suppress the inclusions and improve the quality of crystal with higher transparency.