Alkaline earthides based on 15-crown-5 ether with remarkable NLO response Annum Ahsan, Sehrish Sarfaraz, Mazhar Amjad Gilani, Tariq Mahmood, Zaheer Ahmad and Khurshid Ayub Eur. Phys. J. Plus, 137 10 (2022) 1149 Published online: 17 October 2022 DOI: 10.1140/epjp/s13360-022-03308-z