Ultraviolet, blue and singular green upconversion from Gd2Hf2O7 nanocrystals through dopant manipulation

Abstract Despite of several advantages of upconversion luminescence (UCL), their full potential is still not completely and commercially harnessed particularly in generating ultraviolet photon and singular visible light. We have taken up this research problem to overcome the global material crisis and tune the color emission in the same materials. Here in this work, we have designed Gd2Hf2O7 nanocrystals (NCs) and co-doped them with Yb3+-Er3+ (GHO-YE) and Yb3+-Tm3+ (GHO-YT) using a molten salt synthesis. Raman spectroscopy data suggest a defect fluorite structure for both GHO-YE and GHO-YT NCs. The GHO-YE NCs display unique UCL phenomenon by converting near infrared (NIR) photon into singular green emission by back transferring host defect and 4F9/2 → 4I15/2 red photon to 4S3/2 → 4I15/2 transition. On the other hand, the GHO-YT NCs show multiple ultraviolet bands and intense blue emission upon NIR irradiation. The UC processes have been further investigated in detail by pump power dependence measurements and confirmed as two-photon absorption process for both samples. This work will not only be boon to the global community working on upconversion phosphors but also highlight the importance of UCL NCs for societal applications towards lighting and imaging technologies.