Electron. Mater. Lett., Vol. 9, No. 5 (2013), pp. 615-620 Red Upconversion Luminescence and Paramagnetism in Er/Yb Doped SnO 2 Shweta Sharma, Jyoti Shah, R.K. Kotnala, and Santa Chawla* CSIR-National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi - 110012, India (received date: 27 November 2012 / accepted date: 22 February 2013 / published date: 10 September 2013) Red upconversion luminescence has been introduced in functional semiconductor SnO2 by doping rare earth ions Er 3+ and Yb 3+ and using 980 nm diode laser as pump source. High temperature solid state reaction leads to incorporation of trivalent lanthanide ions in SnO2. For high concentrations of lanthanide doping, partial reduction of Sn 4+ to Sn 2+ occurs for charge compensation making the material system SnO2-SnO alloy. Upconverting SnO2 exhibits paramagnetic characteristics with magnetization increasing with introduction of trivalent rare earth ions Er 3+ /Yb 3+ . Keywords: up conversion luminescence, semiconductor, rare earth, paramagnetism 1. INTRODUCTION Rare earth (RE) doped multifunctional luminescent semi- conductors is a promising new class of materials that can have important applications in areas like solar cells, [1] optoelectronic devices, [2] biological systems [3] and drug delivery. Frequency up conversion (UC) luminescence plays an important role in infra red (IR) to visible spectrum modification and such phosphors have been shown to enhance efficiency of solar cells by harnessing otherwise unutilized solar IR energy for photovoltaic conversion. [4] A functional semiconductor like SnO 2 with wide band gap (3.6 eV) holds special interest due to its novel properties and applications such as transparent conducting electrode, gas sensing, solar photovoltaic conversion, photo catalysis etc. [5-11] . Because of such wide applicability, SnO 2 micro and nano structures and their optical properties have been reported extensively. [12-17] The present work endeavors to introduce new properties in SnO 2 by doping with trivalent rare earth ions Er 3+ and Yb 3+ - well known emitter and sensitizer for UC luminescence. UC luminescence has been reported mostly in insulating fluoride and oxide hosts doped with rare earth emitters Er 3+ , Tm 3+ , Ho 3+ etc with Yb 3+ as sensitizer due to its efficient resonant absorption of IR (~980 nm) radiation and transfer to ladder like energy levels of RE emitter. [18,19] The phenomenon of up conversion under such excitation has been reported for YLiF 4 :Tm 3+ ,Yb 3+ ; Y 2 O 2 S:Yb,Ho; [20,21] Y 2 O 3 : Er 3+ ,Yb 3+ nanorods and Er 3+ ,Yb 3+ codoped LaPO 4 nanocrystals; [22,23] NaYF 4 :Er 3+ ,Yb 3+ core/ shell nanoparticles [4] ; Y 2 O 3 , ZrO 2 , when doped with Er 3+ ; [18,19] Tm 3+ /Er 3+ /Yb 3+ tri-doped CaF 2 phosphors with white light emission, [29] ZrO 2 : Er 3+ , Yb 3+ nanocrystals with red (650 - 685 nm) and green UC emission (520 - 560 nm). [24,25] Blue, green, and red UC emissions were observed in Er 3+ doped ZnO nanocrystals annealed at different temperatures under near-infrared light (808 nm) excitation. [26] Porous silicon (PSL) also exhibits a strong visible luminescence under IR radiation. [27,28] SnO 2 : Er 3+ has shown UC luminescence and waveguide properties and has also shown applications in optical amplifiers and electroluminescent devices. [30] The present study shows that rare earth lanthanide doping in SnO 2 particles not only make them up convert IR light to red, they also become paramagnetic thus making them bi- functional UC fluorescent, magnetic semiconductor. A bi- functional non toxic semiconductor such as trivalent RE doped up conversion luminescent SnO 2 could have important application in spintronics in addition to holding special advantage for application in biological systems due to negligible autofluorescence and photo bleaching with IR excitation compared to down conversion phosphor nano- particles (NP). The synthesis, structural, luminescence and magnetic properties of SnO 2 doped with Er and Er,Yb ions have been described. 2. EXPERIMENTAL PROCEDURE 2.1 Synthesis of undoped and doped SnO 2 particles by Solid state reaction method All the precursor materials have been used as obtained without any further purification. For synthesis of undoped SnO 2 nanoparticles by solid state reaction method commercial Tin oxide (1 M) was weighed and packed in alumina boat and fired at 1450°C in high temperature furnace for 3 hours in air atmosphere. For synthesis of SnO 2 doped with erbium (Er), Er 2 O 3 was used (2 mol. %) as substitutional dopant in DOI: 10.1007/s13391-013-2230-3 *Corresponding author: santa@nplindia.org ©KIM and Springer