Article pubs.acs.org/IC
Host-Sensitized and Tunable Luminescence of GdNbO4:Ln3+ (Ln3+ = Eu3+/Tb3+/Tm3+) Nanocrystalline Phosphors with Abundant Color Xiaoming Liu, Chen Chen, Shuailong Li, Yuhua Dai, Huiqin Guo, Xinghua Tang,* Yu Xie, and Liushui Yan* School of Environment and Chemical Engineering, Nanchang Hangkong University, Nanchang 330063, P. R. China S Supporting Information *
ABSTRACT: Up to now, GdNbO4 has always been regarded as an essentially inert material in the visible region with excitation of UV light and electron beams. Nevertheless, here we demonstrate a new recreating blue emission of GdNbO4 nanocrystalline phosphors with a quantum efficiency of 41.6% and host sensitized luminescence in GdNbO4:Ln3+ (Ln3+ = Eu3+/Tb3+/Tm3+) nanocrystalline phosphors with abundant color in response to UV light and electron beams. The GdNbO4 and GdNbO4:Ln3+ (Ln3+ = Eu3+/Tb3+/Tm3+) nanocrystalline phosphors were synthesized by a Pechini-type sol−gel process. With excitation of UV light and low-voltage electron beams, the obtained GdNbO4 nanocrystalline phosphor presents a strong blue luminescence from 280 to 650 nm centered around 440 nm, and the GdNbO4:Ln3+ nanocrystalline phosphors show both host emission and respective emission lines derived from the characterize f−f transitions of the doping Eu3+, Tb3+, and Tm3+ ions. The luminescence color of GdNbO4:Ln3+ nanocrystalline phosphors can be tuned from blue to green, red, blue-green, orange, pinkish, white, etc. by varying the doping species, concentration, and relative ratio of the codoping rare earth ions in GdNbO4 host lattice. A single-phase white-light-emission has been realized in Eu3+/Tb3+/Tm3+ triply doped GdNbO4 nanocrystalline phosphors. The luminescence properties and mechanisms of GdNbO4 and GdNbO4:Ln3+ (Ln3+ = Eu3+/Tb3+/Tm3+) are updated.
1. INTRODUCTION
Rare earth ions have been playing an significant role in modern lighting, display, biological labels, fluorescent falsification-prevention, and other optical-electronic devices owing to their excellent luminescence properties based on their 4f−4f or 5d−4f transitions.18,19 Typical rare earth ions, such as Eu3+, Tb3+, and Tm3+, are widely used as red, green, and blue three primary colors dopants to obtain desired phosphors. For example, the trivalent europium ion (Eu3+) is a famous redemitting activator owing to its 5D0-7FJ transitions (J = 0, 1, 2, 3, 4).20,21 The terbium ion (Tb3+) usually gives characteristic green luminescence coming from its transitions of 5D3,4-7FJ (J = 3, 4, 5, 6).22 For thulium ion (Tm3+), it often gives prominent blue emission with high color purity mainly origin from the transitions of 1D2-3F4 and 1G4-3H6.23 Lanthanide niobates with fergusonite structure have attracted a great deal of attention due to their interesting physical properties, such as high dielectric constants, commendable electro-optical, photoelastic, and nonlinear properties as well as good mechanical and chemical stability.24−26 Up to now, GdNbO4 has been regarded as an essentially inert material in the visible region with excitation of UV light and electron beams. Blasse and Bril have explained that the nonluminescence of GdNbO4 (or NbO6 group) is ascribed to the energy transfer from NbO6 group to gadolinium ions, and then,
In recent years, white light-emitting diodes (WLEDs), known as promising candidates to replace conventional incandescent and fluorescent lamps, have aroused significant attention due to its excellent properties, such as small size, fast switching, high luminous efficiency, low energy cost, environmental friendliness, and long lifetime.1−5 Currently, the combination of blue InGaN LED chip with yellow phosphor Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce3+) is the most popular approach to get white light. Unfortunately, warm white-light illumination usually cannot be achieved by this approach because of the deficiency of red emission.6−9 An alternative way to solve this problem is to make WLEDs by coating a UV LED (300−410 nm) with a mixture of red, green, and blue emitting phosphors, which can provide superior color uniformity with a high color-rendering index and excellent quality of white light. However, owing to the strong reabsorption of blue light by red-/green-emitting phosphors and large Stokes shift, the luminous efficiency is low in this approach.10−12 To overcome these problems, researchers have been developing single composition white-emitting phosphors, which are excited by UV-LED to prevent the cross-color, instability of color temperature, and expensive cost problems.13,14 Therefore, high efficient single-component phosphors which can be excited by UV and/or near-UV chips are of high interest to be explored for both fundamental research and practical applications.15−17 © XXXX American Chemical Society
Received: July 8, 2016
A
DOI: 10.1021/acs.inorgchem.6b01637 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
10 h. Between the firing, the samples were reground. The final sample was ground into powder for next measurements.32,33 The prepared sample was marked with GdNbO4−SSR. The crystalline phases of the prepared Eu3+, Tb3+, Tm3+ single doped, doubly doped, and triply doped GdNbO4 nanocrystalline phosphors were investigated by an X-ray diffractometer (XRD, Bruker D8 ADVANCE) using graphite monochromatized Cu-Kα (λ = 0.15406 nm) radiation. The morphologies of the samples were examined by a field-emission scanning electronic microscope (FESEM, JSF-6700) and high resolution transmission electron microscopy (HR-TEM, JEOL 2010). Diffuse reflectance spectra were obtained using a UV−visible diffuse reflectance spectrometer (JASCO V-560) equipped with an integration sphere using Spectralon as a reference. The PL excitation and emission spectra were measured using a Hitachi F-7000 spectrophotometer equipped with a 150 W xenon light source. The CL measurements were examined in an ultrahigh-vacuum chamber (
