Investigation of concurrent emissions in visible, UV and NIR region in Gd2O2S: Er, Yb nanophosphor by diverse excitation wavelengths as a function of firing temperature

Abstract

Herein, we report the concurrent emissions in Visible, Ultraviolet (UV) and Near-Infrared (NIR) range by a single Gadolinium Oxysulphide (Gd2O2S) nanophosphor doped with Erbium (Er3+) – Ytterbium (Yb3+) and the optimization of its multiplexed photoluminescence (PL) profile as a function of firing temperature. The multimode emissions sensitized by an assortment of excitation wavelengths – 285 nm, 450 nm, 808 nm, and 1064 nm, revealed the roles of complex energy transition processes between several Er3+ excited states and single Yb3+ excited state. Stoke's shift of excitation by 285 nm in the visible region giving dominant violet emission along with green and red emissions portrayed the downconversion (DC) characteristics of the synthesized nanophosphor. The excitation by 450 nm produced emissions with anti-Stoke's shift to UV region; and, Stoke's shift to visible and NIR bands; disclosing the presence of simultaneous upconversion (UC), DC and NIR Quantum cutting (NIR-QC). Apart from usual UC of 808 nm excitation in the visible region, a vast anti-Stoke's shift to UV region displaying high-energy UC along with DC to NIR band displayed the multifarious excitation conversion by Gd2O2S nanophosphor. Incidence of 1064 nm also leads to large anti-Stoke's shift to UV, visible and NIR region strengthening the upconverting profile of the fabricated nanophosphor. The emission intensity of multiplexed PL investigated as a function of firing temperature (1000°C–1250 °C) divulged the optimization cycle of the synthesized nanophosphor for each excitation wavelength. The nanophosphors fabricated at lower firing temperature were found to be more efficient in absorbing and converting higher frequency photons whereas for upper firing temperatures the lower frequency photons were more favored. The obtained broad spectral conversion by a single Gd2O2S nanophosphor can be exploited to give a tailormade phosphor for the desired application such as sunlight harvesting, NIR detectors, biomedical imaging, and others.