Elsevier

Ceramics International

Volume 41, Issue 9, Part A, November 2015, Pages 11279-11286
Ceramics International

Multicolored photoluminescence and structural properties of zirconium oxide films co-doped with Tb3+ and Eu3+ ions

https://doi.org/10.1016/j.ceramint.2015.05.084Get rights and content

Abstract

The photoluminescence and structural properties of ZrO2 films doped with Eu3+ and Tb3+ ions, deposited by ultrasonic spray pyrolysis technique, are reported. X ray diffraction analysis showed that the films are polycrystalline and exhibit the ZrO2 tetragonal metastable phase. The surface morphology characteristics of the films are strongly dependent on the deposition temperature, going from a rough surface formed by ramifications at low temperatures to a denser material with ramifications and the appearance of spherical features at higher temperatures. In addition, the elemental composition of the films as determined by energy dispersive spectroscopy, is reported. The photoluminescence spectra present the characteristic emission peaks associated with the Tb3+ and Eu3+ dopants as well as a broad emission peaked at 440 nm associated with radiative transitions within the ZrO2 matrix. As the deposition temperature is increased, it was observed an increasing intensity of the photoluminescence emission. Also a concentration quenching was observed for both dopants. The photoluminescence emission spectra for the ZrO2 films co-doped with Eu3+ and Tb3+ ions, showed emission lines that are a combination of those observed for each ion individually plus the blue broad band associated with the host lattice. Decay times were measured for double doped samples. The CIE chromaticity diagrams for these films showed colors falling in the blue, green, yellow, red-orange, bluish-white and yellowish-white regions depending on the doping characteristics of the films.

Introduction

Luminescent materials play an important role in the development of new applications such as different types of flat panels and projection displays and white light lamps. The performance of display panels is strongly related to the nature of the phosphor, to its chemical and physical stability and the kind of optical centers active in them. There are several types of flat luminescent display technologies under development, among them are: plasma display panels (PDP), in which three primary color phosphors are excited by vacuum ultraviolet (VUV) radiation generated by a plasma; field emission displays (FED), in which the luminescent material is irradiated by low-energy electrons; and thin film electroluminescence displays (ELD), in which electrons injected into the luminescent layer are accelerated by an applied field up to the energy necessary to excite luminescent centers [1], [2], [3]. On the other hand, white light sources of high-efficiency, high brightness and low energy consumption are required for outdoor illumination and full-color display applications. During the last 10 years white LEDs have become very important lighting sources and the development of phosphors for white LEDs and colored light generation must be considered an important market driver in the future [4], [5]. Metal oxides are very versatile materials that may play an important role in the phosphors design and synthesis technology. Among them, zirconium oxide is a material whose properties make it an excellent candidate for applications in the field of the optics in general, due to its high refraction index (~2.17) and high transparency for visible-ultraviolet light. In the case of luminescent applications, the ZrO2 has shown to be a good host for a great variety of rare earth ions [6], [7], [8] because of its wide band gap of about 5.2–5.8 eV and their low phonon frequency of about 470 cm−1, which increases the probability of occurrence of radiative transitions when this material is doped with rare earths or transition metals. There are some studies on ZrO2 and HfO2 powders optically activated with Eu3++Tb3+ ions [9], [10] but, to our best knowledge, research on films of ZrO2: Eu3++Tb3+ is scarce or nonexistent. Luminescent films, as compared with materials in powder form, have some advantages such as good adhesion to the substrate, unaltered properties throughout the covered area, better thermal stability, and minimal optical scattering with less material [11]. More than one method has been used to synthesize ZrO2 films [12], [13], among them are: sol–gel, atomic layer deposition, solid state reaction and spray pyrolysis [14], [15], [16]. The ultrasonic spray pyrolysis has been successfully used to deposit different metal oxide films [17], [18]. This is a low cost technique with high deposition rates, easy to operate and with the capability to carry out depositions on large areas.

This work reports the photoluminescence characteristics of zirconium oxide films co-doped with different concentrations of Eu3+and Tb3+ ions, with the purpose of achieving light photoemission of various colors (including white light) by tuning the concentrations of the dopants and selecting the excitation wavelength. In addition, the surface morphology, the chemical composition and the crystalline structure of the films were analysed as a function of the deposition parameters.

Section snippets

Materials and methods

The un-doped films were deposited using ZrCl2·8H2O (99.99% Aldrich), dissolved in deionized water, the solution molarity was 0.6M. The films were deposited on corning glass, at deposition temperatures (Ts) from 350 °C to 600 °C, in steps of 50 °C; using filtered air as carrier gas at a rate of 10 l/min. The ultrasonic frequency was 1.6 MHz. The deposition time was adjusted in the range of 5–6 min in order to obtain a thickness of approximately 5 μm, as measured by a Sloan Dektak IIA profilometer, for

Results and discussion

Fig. 1 shows the indexed X-ray diffraction patterns, for the ZrO2 un-doped films as a function of the deposition temperature. It can be observed that all the films have certain degree of crystallinity; even those deposited at low temperatures; the diffractograms show wide peaks with relatively low intensity, which can mean that the films are formed by very small crystals or a combination of these with an amorphous phase. The films deposited at 450, 500, 550 °C and 600 ºC, show better defined

Conclusions

Un-doped ZrO2 and single- and double-doped ZrO2: RE (where RE=Tb3+ and Eu3+) films have been synthesized using a simple, economical and versatile ultrasonic spray pyrolysis technique (using short deposition times and relatively low deposition temperatures). The ZrO2: Tb3+ (10 at%): Eu3+ (5 at%) films showed white PL as a function of Tb/Eu ratios and the excitation wavelengths. The results thus provide a practical basis for the design of white light illumination sources by blending this kind of

Acknowledgements

The authors wish to thank Adriana Tejeda for her support in carrying out the XRD study; J. Romero-Ibarra for SEM-EDS measurements; Prof. Prashant Patil for the CIE program, also to A. Báez-Rodríguez, J.M. García-León, M. Guerrero and Z. Rivera for their technical support. Also we thank to SIP-IPN for the financial support through the project number 20140503. Finally, to CONACYT for the financial support given during this work.

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