Luminescent Properties of YNbO[sub 4]:Bi Phosphors

Abstract

Field emission displays (FEDs) are currently being explored as potential flat panel displays. Low power display markets are highly competitive, therefore low-voltage cathodoluminescent (CL) phosphors have become an important area of phosphor research. For the application of full color FEDs, efficient new phosphor materials with good chromaticity and high brightness must be developed. We have focused our attention on the Y 2 O 3 -Nb 2 O 5 system regarding requirements of new materials for low-voltage blue phosphors.According to the Y 2 O 3 -Nb 2 O 5 phase diagram, a compound with the composition YNbO 4 (ϭY 2 O 3 иNb 2 O 5 ) and a berthollide phase based on Y 3 NbO 7 (ϭ3Y 2 O 3 иNb 2 O 5 ) were found in this system. 1,2 Contrary to the cubic phase of Y 3 NbO 7 with a fluorite-related structure, the compound YNbO 4 has two polymorphs, 3-6 low-temperature monoclinic (M-phase, fergusonite structure) and high-temperature tetragonal (T-phase, scheelite structure) forms. The monoclinic form of YNbO 4 transforms into a tetragonal structure at 900ЊC. 1 Yttrium niobate is optically active and exhibits a strong and broad blue emission band, attributed to a charge transfer transition of the tetrahedral [NbO 4 ] 3Ϫ molecular ion. There have been some investigations either on Bi activated yttrium niobate by Blasse and Bril 7-9 or on rare earth niobate compounds, in particular the GdNbO 4 :Bi phosphor by Grisafe and Fritsch. 10 However, such efforts did not meet the requirement for actual display applications. Later Ropp 11 reported systematic studies of niobates doped with rare earth ions and indicated that yttrium niobates activated by rare earth ions always showed lower efficiency than the host material as a self-activated phosphor. Recent studies by Vecht et al. [12][13][14]16 showed that the bismuth activated yttrium niobate could be used as a low-voltage saturated blue phosphor for FEDs.We therefore studied the synthesis of blue emitting phosphors in the Y 2 O 3 -Nb 2 O 5 system and examined the relationship of photo-and cathodoluminescent properties with their structures. In this study, yttrium niobate phosphors doped with Bi were prepared by the solidstate reaction technique. The optimization of synthetic processes and the effect of Y/Nb ratio on the luminescent properties were investigated, specifically.Even though YNbO 4 and YNbO 4 :Bi are well-known phosphors, there have been no theoretical approaches to interpret their luminescence. Thus we have initiated calculations on the electronic structure of YNbO 4 using the density functional method. The excitation and emission spectra of YNbO 4 and YNbO 4 :Bi phosphors are interpreted with the calculated results regarding the charge transfer gap of YNbO 4 and the effect of bismuth in YNbO 4 :Bi phosphor.Experimental Preparation of phosphor.-Bismuth doped YNbO 4 phosphors were made from the starting materials Y 2 O 3 , Nb 2 O 5 , and Bi 2 O 3 (all supplied by the High Purity Chemical Laboratory Co. Ltd., at 99.99% purity) powders. Required amounts of the corresponding powders...

Broadband downconversion based near-infrared quantum cutting via cooperative energy transfer in YNbO4:Bi3+, Yb3+ phosphor

“…The Bi 6s6p is located at a lower energy level than that of Nb 4d. The calculated partial densities of states show that the Bi 6s 2 valence band levels lie just above the O 2p valence band levels and the Bi 6s 2 levels overlap with the O 2p ones [29,32]. Thus, the electron in O 2p (Bi 6s 2 ) can be excited to Nb 4d and Bi 6s6p.…”

“…The concentration of Bi 3+ is fixed at the optimal doping level of 1 mol %. The photoluminescence excitation [29]. The Bi 6s6p is located at a lower energy level than that of Nb 4d.…”

“…RE niobates are efficient hosts for Bi 3+ known as self-activated luminescent materials. Introducing Bi 3+ into YNbO 4 shifts the emission band to the longer wavelength of 440 nm [29], making YNbO 4 :Bi 3+ a suitable and efficient blue phosphor for field emission display (FED) application [30]. Compared with the undoped YNbO 4 , the blue photon emitted from YNbO 4 :Bi 3+ matches much better the energies of two Yb 3+ : 2 F 7/2 → 2 F 5/2 transitions, making the CET from one Bi 3+ to two Yb 3+ theoretically possible and potentially more efficient.…”

Photoluminescence properties of Y0.5−xGd0.35Eu0.15BixNbO4 (0≤x≤0.30) and Y0.35Gd0.35Eu0.15Bi0.15Nb1−yPyO4 (0≤y≤0.20) phosphors

“…Niobates, being one of efficient hosts, are well-known as self-activated luminescent materials. Via introducing the Bi 3+ ion into YNbO 4 phosphors, the emission band will be shifted to the longer wavelength [11]. According to some previous reports [12], the Bi 3+ ion can be also used as the sensitizer to strengthen and broaden the near ultraviolet excitation bands of the Eu 3+ luminescence.…”

Novel YNbO4:RE3+ (RE=Sm, Dy, Er) microcrystalline phosphors: Chemical co-precipitation synthesis from hybrid precursor and photoluminescent properties

“…YNbO ceramics to obtain the high roughness [30][31][32][33] and some reports were reported on the crystal characterization [34][35][36]. Besides, YNbO 4 :Bi 3+ has been verified to be potential blue phosphors for cathodluminescence [37][38][39][40]. While for the photoluminescent properties for YNbO 4 activated by rare earth ions has rarely been reported except for Eu 3+ enters [41].…”