title: New perspective in garnet phosphor: low temperature synthesis, nanostructures, and observation of multimodal luminescence.
abstract: Herein, we report a new concept for garnet materials in terms of the synthesis of nanocrystalline structure at low temperatures and its multimodal luminescence processes. Terbium- and ytterbium-ion-codoped yttrium gallium garnet nanophosphors have been synthesized via solution combustion technique; nearly pure phase nanophosphor samples were obtained. The synthesized nanophosphor shows efficient multimodal upconversion (UC), downshifting (DS), and quantum cutting (QC)/downconversion (DC) luminescence, which is a new paradigm in garnet material. The garnet nanophosphor shows strong green emission through DS and UC processes both. Furthermore, cooperative energy transfer (CET) has been described in detail, and a possible mechanism for the QC process is also proposed. A UV/blue photon absorbed by Tb(3+) ion splits into two near-infrared photons (wavelength range 900-1040 nm), emitted by a Yb(3+) ion pair, with an efficiency of more than 100%. The Yb(3+) concentration dependent ET from Tb(3+) to Yb(3+) has been verified using time domain analysis. An ET efficiency as high as 28% and a corresponding QC efficiency of about 128% (for 15 mol % of Yb(3+) concentration) have been attained. Such a multimode emitting nanophosphor could be very useful in display devices and for enhancing the conversion efficiency of next generation solar cells via spectral modification etc.
authors.affiliation: Department of Physics, Banaras Hindu University , Varanasi-221005, India.
authors.forename: Kavita
authors.initials: K
authors.lastname: Mishra
authors.forename: Sunil Kumar
authors.initials: SK
authors.lastname: Singh
authors.forename: Akhilesh Kumar
authors.initials: AK
authors.lastname: Singh
authors.forename: Monika
authors.initials: M
authors.lastname: Rai
authors.forename: Bipin Kumar
authors.initials: BK
authors.lastname: Gupta
authors.forename: Shyam Bahadur
authors.initials: SB
authors.lastname: Rai