Sensors and Actuators B 243 (2017) 579–588 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb Europium-doped gadolinium oxide nanoparticles: A potential photoluminescencent probe for highly selective and sensitive detection of Fe 3+ and Cr 3+ ions Savita Chaudhary a,∗∗ , Sandeep Kumar a , Ahmad Umar b,c,∗ , Jasmeet Singh d , Mohit Rawat d , S.K. Mehta a a Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, Chandigarh 160014, India b Department of Chemistry, College of Science and Arts, Najran University, Najran-11001, Kingdom of Saudi Arabia c Promising Centre for Sensors and Electronic Devices (PCSED), Najran University, Najran-11001, Kingdom of Saudi Arabia d Department of Nanotechnology, Sri Guru Granth Sahib World University, Fatehgarh Sahib, Punjab (140406), India a r t i c l e i n f o Article history: Received 15 October 2016 Received in revised form 22 November 2016 Accepted 1 December 2016 Available online 5 December 2016 Keywords: Europium Gadolinium oxide Photoluminescence sensing Metal ion Recovery studies a b s t r a c t Herein, we report the facile synthesis, characterizations and photoluminescence sensing probe appli- cations of europium (Eu 3+ )-doped gadolinium oxide (Gd 2 O 3 ) nanoparticles. The Eu 3+ - doped Gd 2 O 3 nanoparticles were synthesized by a facile and straight forward chemical synthesis followed by the cal- cination process. Various percent concentrations of Eu 3+ ranging from 1 to 5% was used to dope into the Gd 2 O 3 and calcine them for different time to optimize the photoluminescence properties of the syn- thesized nanoparticles. The synthesized nanoparticles were characterized by several techniques which confirmed that the 5% Eu 3+ - doped Gd 2 O 3 nanoparticles exhibited best structural and optical properties. Thus, due to best structural and optical properties, the 5% Eu 3+ - doped Gd 2 O 3 nanoparticles were used as photoluminescent probe for the detection of Fe 3+ and Cr 3+ ions. The detailed sensing results revealed that the synthesized nanoparticles are quite selective and sensitive towards Fe 3+ and Cr 3+ ions with 99.3% quenching efficiency for 10 ppm Fe 3+ ions and 98.6% quenching efficiency for 40 ppm Cr 3+ ions respec- tively. The detection limit for Fe 3+ and Cr 3+ ions were 1.48 ppm and 6.56 ppm respectively. The utilization of synthesized nanoparticles in real water samples with percentage recovery of >90% in tap water and distilled water and 87% in sewage water has unlocked numerous opening to use such nanomaterial for real water treatment applications. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Recently, lanthanide oxide nanomaterials have attracted great attention from the scientific community due to their fascinating properties and distinctive applications in various areas of science and technology, to name a few, flat panel displays, optical data storage and luminescent devices, high energy radiation detec- tors, biomedical diagnostic and treatment applications, and so on [1–9]. Further, because of the large stoke shifts, narrow emission properties and long luminescent life time, the lanthanide oxide ∗ Corresponding author at: Department of Chemistry, College of Science and Arts, Najran University, Najran, 11001, Kingdom of Saudi Arabia. ∗∗ Corresponding author: Department of Chemistry and Centre of Advanced Studies in Chemsitry, Panjab University, Chandigarh, 160014,India E-mail addresses: schaudhary@pu.ac.in, schaudhary.pu@gmail.com (S. Chaudhary), ahmadumar786@gmail.com (A. Umar). nanomaterials are also used for fluorescent labelling applications [10–13]. Among various lanthanide oxide nanomaterials, gadolin- ium oxide (Gd 2 O 3 ) nanomaterials are considered as one of the most important and promising materials due to their own properties and applications [14]. The presence of highly stable 4f shell with seven unpaired spins in Gd 3+ ions made it one of the efficient materials in luminescence based applications [15–17]. The significant 4f–4f transitions in Gd 2 O 3 have the tendency to generate visible and infrared emission and the forbidden nature of these transitions has the ability to influence the low molar absorptivity values in Gd 2 O 3 [18] . Thus, to avoid such restrictions, Gd 2 O 3 nanoparticles are doped with another ion to enhance its luminescence efficiency. Due to the higher absorption efficacy and lower diffusion barrier, Eu 3+ ions are considered as efficient dopants which can tailor the optical properties of lanthanide oxide nanomaterials; specially Gd 2 O 3 ; and can be used for various specific applications [19,20]. Due to excel- lent properties and wide applications, Eu 3+ -Gd 2 O 3 nanomaterials http://dx.doi.org/10.1016/j.snb.2016.12.002 0925-4005/© 2016 Elsevier B.V. All rights reserved.