Comment to the article “Analysis of photoluminescence, UV absorbance, optical band gap and threshold voltage of TiO2 nanoparticles dispersed in high birefringence nematic liquid crystal towards its application in display and photovoltaic devices” [J. Lumin. 192 (2017) 33–39] - Roy, Joy Sankar [UNESP] (Elsevier, 2018)