Controlled surface distribution and luminescence of YVO4:Eu3+ nanophosphor layers

Abstract

A method of dispersing YVO 4 : Eu quantum dots ͑QDs͒ as uniform two-dimensional ͑2D͒ layers with a high degree of homogeneity is presented. Annealing at 773 K resulted in coalescence of QDs to form nanoclusters with size of ϳ25 nm with an improved photoluminescence and ϳ80% transmittance at 800 nm. An efficient 5 D 0 -7 F 2 transition and lifetimes of ϳ1038 s for the characteristic Eu 3+ emission were observed. The absorption and emission peaks showed a slight blueshift, due to quantum-size effect, as compared to that for the bulk counterpart. Our method of 2D layer deposition is useful to enhance spectral response of the solar cells. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2973163͔ Quantum dots ͑QDs͒ have attracted much attention due to their potential applications for many high performance devices, 1 viz., the Si-solar cell 2 and QD based light emitting diodes.3 Chemically synthesized 4,5 QDs with precise size ͑Ͻ5 nm͒ control and a suitable organic/inorganic cap are currently available for many practical applications. 6 The QDs of phosphor materials could be even more interesting as they do not scatter light and show enhanced emission efficiencies 7 and radiative lifetime shortening. 8 The spatially distributed phosphor QDs can act as a thin layer having good optical transparency and high emission characteristics. Such a layer can be useful for increasing the power conversion efficiency of a solar cell. The objective of the present study is to fabricate highly transparent and luminescent two-dimensional ͑2D͒ layer using inorganic capped YVO 4 QDs that possess the advantages of quantum-size effect. Annealing treatments performed to the layers not only initiated the nanocluster formation but also provided a proper thermal encapsulation, adherence, and increased PL emission related efficiencies.In utilizing nanoparticles for device technology one of the fundamental issues is how to distribute nanoparticles uniformly over a substrate with a precise control of particle density. In most of the studies, the self-assembly scheme has been employed using the chemical interaction between the nanoparticles and the substrate.9-11 This method is effective in achieving a dense layer of nanoparticles. However, the control of the particle density is difficult at submonolayer regime. Moreover, special chemical treatments of the substrate surface are needed and the results are sensitive to local chemical environment with enhanced defect susceptibility.In this letter, we demonstrate the fabrication of uniformly distributed sodium hexametaphosphate ͑SHMP͒ capped YVO 4 : Eu nanophosphor layer with controlled particle density using the conventional spin-coating method followed by annealing treatment.It is well known that the OH − groups show significant luminescence quenching behavior for most of the inorganic QDs.12 Commonly, researchers synthesize YVO 4 : Eu nanophosphor by wet-chemical methods and protect the surface atoms by phosphate capping followed by redispersion in deionized water. This results in fully hydrat...

Red enhanced YAG:Ce, Pr nanophosphor for white LEDs

“…This explains the observed luminescence decay time in the order of nanoseconds. For the Ce 3þ emission in YAG, decay time is reported to be 10-70 ns [17,18,20] has a much longer decay time (hundreds of microsecond to millisecond) due to forbidden nature of electric dipole transition [21,22] as is observed in the present case. The measured luminescence decay of 610 nm emission for different concentrations of Pr in YAG:Ce,Pr under microsecond pulsed 460 nm excitation is shown in Figure 5(b), the initial part of the decay and its variation with Pr concentration is shown in the inset.…”

Nanophosphor Coatings: Technology and Applications, Opportunities and Challenges

“…The screen printing technique, in which a concentrated phosphor ink containing a liquid organic vehicle is applied to a substrate through a mesh screen and then calcinated to remove organic additives, could also be implemented for nanophopshor plasma display panels (Song et al, 2012a;Song et al, 2012b), field emission screens , and X-Ray imaging systems . Sol-gel coatings and pastes can be applied by dip-coating (Pang et al, 2003;Wu et al, 2007) or spin-coating (Bedekar et al, 2010;Buissette et al, 2006;Huang et al, 2012a;Khan et al, 2008;Klausch et al, 2012;Psuja et al, 2009;Revaux et al, 2011b;Song et al, 2011). Wet spraying, known for many decades (Sadowsky, 1949), could be adopted for the deposition of nanophosphors as well (Fleury et al, 2012;Revaux et al, 2011a).…”

“…Such coatings are placed in front of the cell and ideally they should not interfere with light which does not need to be converted. Obviously, transparency of the converter layer is strongly desired so that nanophosphor coatings should be preferred over conventional phosphors (Huang et al, 2012a;Khan et al, 2008;Peng et al, 2011;Takeshita et al, 2009). Upconverting SCs perform a complimentary function of absorbing low-energy photons, for which the solar cell itself is transparent, and convert to photons of shorter wavelength so that they could also be absorbed by the solar cell.…”

“…The group includes various realizations of chemical precipitation (Bazzi et al, 2004;Buissette et al, 2006;Khan et al, 2008;Lebbou et al, 2005;Mutelet et al, 2011;, hydrothermal (Jacobsohn et al, 2007;Huang et al, 2012b;Riwotzki and Haase, 2001;Song et al, 2011; or solvothermal (Gong et al, 2013;Kasuya et al, 2007;Nyman et al, 2009;Vorsthove and Kynast, 2011) synthesis, thermal (Si et al, 2006;Ye et al, 2010) or microwave (Dai et al, 2011) decomposition, solgel methods (Back et al, 2012;Dhanaraj et al, 2001;Eid et al, 2005;Gupta et al, 2010;Zhang et al, 2002), inverse micelle method (Barnes et al, 2000;Hirai et al, 2004), laser ablation in liquid media (Mhin et al, 2009;, and combustion synthesis (Jacobsohn et al, 2007;Qi et al, 2002;Vu et al, 2007;Ye et al, 2009;Zhang et al, 2003), including flame-assisted spray pyrolysis, which is also capable of producing nanoparticles if the precursor solution is appropriately modified (Purwanto et al, 2008).…”

Facile synthesis and step by step enhancement of blue photoluminescence from Ag-doped ZnS quantum dots

“…The optical properties in QD systems is useful for various applications such as full colour display devices, white LEDs, photovoltaic cells, bioimaging and other medical related applications [2][3][4][5][6][7]. Over the decades, zinc sulphide (ZnS), a wide and direct band gap (Eg bulk = 3.6 eV) semiconductor having exciton Bohr radius, RB = 2.5 nm, has been studied to modify the color of emission using dopants such as Mn 2+ and isovalent impurities or complexes [8][9][10][11][12].…”