Next Article in Journal
Experimental-Numerical Failure Analysis of Thin-Walled Composite Columns Using Advanced Damage Models
Next Article in Special Issue
Exploring the Impact of Structure-Sensitivity Factors on Thermographic Properties of Dy3+-Doped Oxide Crystals
Previous Article in Journal
Non-Invasive Topical Drug-Delivery System Using Hyaluronate Nanogels Crosslinked via Click Chemistry
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Materials
Volume 14
Issue 6
10.3390/ma14061505
materials-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Red Y2O3:Eu-Based Electroluminescent Device Prepared by Atomic Layer Deposition for Transparent Display Applications

by
José Rosa
1,
Mikko J. Heikkilä
2,
Mika Sirkiä
1 and
Saoussen Merdes
1,*
1
Beneq Oy, Olarinluoma 9, FI-02200 Espoo, Finland
2
Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014 Helsinki, Finland
*
Author to whom correspondence should be addressed.
Materials 2021, 14(6), 1505; https://doi.org/10.3390/ma14061505
Submission received: 10 February 2021 / Revised: 15 March 2021 / Accepted: 16 March 2021 / Published: 19 March 2021
(This article belongs to the Special Issue Advanced Luminescent Materials and Devices)
Browse Figures
Versions Notes

Abstract

:
Y2O3:Eu is a promising red-emitting phosphor owing to its high luminance efficiency, chemical stability, and non-toxicity. Although Y2O3:Eu thin films can be prepared by various deposition methods, most of them require high processing temperatures in order to obtain a crystalline structure. In this work, we report on the fabrication of red Y2O3:Eu thin film phosphors and multilayer structure Y2O3:Eu-based electroluminescent devices by atomic layer deposition at 300 °C. The structural and optical properties of the phosphor films were investigated using X-ray diffraction and photoluminescence measurements, respectively, whereas the performance of the fabricated device was evaluated using electroluminescence measurements. X-ray diffraction measurements show a polycrystalline structure of the films whereas photoluminescence shows emission above 570 nm. Red electroluminescent devices with a luminance up to 40 cd/m2 at a driving frequency of 1 kHz and an efficiency of 0.28 Lm/W were achieved.

1. Introduction

Inorganic-based electroluminescent (EL) devices have been extensively studied for transparent flat panel display applications due to their distinct characteristics. Such technology allows for the creation of displays capable of withstanding harsh environments thanks to their exclusively solid structure, which leads to a high level of vibration and mechanical shock resistance [1]. Additionally, the electroluminescence phenomenon, which is not affected by temperature, allows EL devices to operate in a wide range of temperatures [2]. Furthermore, the ability to use alternating current to drive EL devices prevents charge accumulation, leading to long operating lifetimes [3].
Because the abovementioned characteristics are difficult to achieve with technologies such as organic-light emitting diodes (OLEDs), inorganic-based electroluminescent displays are very attractive from the commercial point of view. LUMINEQ thin film electroluminescent (TFEL) rugged displays and their transparent version TASEL displays are good examples of such commercial products which have been incorporated in industries such as automotive, industrial vehicles, and optical devices.
While yellow and green TFEL and TASEL displays are commercially available, demand for red EL devices has been increasing. Transparent red electroluminescent displays could, for example, be integrated to heavy vehicles, enabling them to display warning signs more effectively, thereby increasing the safety of operators. In the past, some attempts to develop red electroluminescent devices have been made by integrating phosphors such as CaS:Eu [4,5,6], CaY2S4:Eu [7], β-Ca3(PO4)2:Eu [8], and ZnS:Sm,P [9] into the classic dielectric/semiconductor/dielectric (DSD) EL device structure. Red EL devices, with phosphors such as Eu2O3 [10], Ga2O3:Eu [11,12], and IGZO:Eu [13], were also developed using alternative device structures. However, only the use of a color filter with the yellow ZnS:Mn phosphor resulted in sufficiently high red luminescence to be used in commercial products [14]. This solution is unfortunately not suitable for transparent display applications as the use of filters reduces the overall transparency of the device.
Among the currently available red inorganic phosphors, Y2O3:Eu and Y2O2S:Eu are the most efficient [15,16]. Y2O3 and Y2O2S are known for their good chemical and photochemical stability. Furthermore, because Y3+ and Eu3+ have similar dimensions of the ionic radii, rare-earth materials such as Eu3+ can easily be integrated into Y2O3 and Y2O2S matrices [17]. However, Y2O3 exhibits a high electrical resistivity, with reported values in the 1011–1012 Ωm range [18], which makes it incompatible with the classic DSD electroluminescent device structure. Nevertheless, several papers have demonstrated the successful use of Y2O3 and Y2O2S in red and green electroluminescent devices using multilayer structures where ZnS is used as a carrier accelerating layer [19,20].
Y2O3:Eu thin film phosphors can be grown by various methods such as wet chemistry [21], laser vaporization [22], hydrothermal [23], microwave hydrothermal [24,25], chemical precipitation with calcination [26], co-precipitation [27], Pechini [28], sol–gel [29,30], and pulse laser deposition [31] methods. Atomic layer deposition (ALD) is a well-known method that allows the growth of uniform and dense films with well-controlled stoichiometry and high chemical stability. Moreover, ALD, which is the method used for the fabrication of commercial electroluminescent displays, offers the advantage of an all-in-one growth step for the dielectric and phosphor layers in a DSD structure, thereby improving device resistance to moisture [1,32]. Years of advances in ALD technology have allowed the use of more elements and chemical precursors for the development of novel processes. As a result, opportunities for the fabrication of high-quality phosphors, and consequently more efficient electroluminescent devices, may arise in the future.
In a previous paper, we reported the growth of blue and red Y2O3-xSx:Eu phosphors by ALD [33]. In this work, we focus on the fabrication and the performance evaluation of Y2O3:Eu-based multilayer structure electroluminescent devices that can potentially be used in red transparent display applications.

2. Materials and Methods

Atomic layer deposition processes for Y2O3, Eu2O3, Al2O3, and ZnS thin films were first developed on (100)-oriented Si substrates. All the films were grown at 300 °C in a Beneq TFS-200 ALD-reactor (Beneq Oy, Espoo, Finland) at a pressure of about 1.3 mbar. (CH3Cp)3Y (98%, Intatrade, Anhalt-Bitterfeld Germany), Eu(thd)3 (THD = 2,2,6,6-tetramethyl-3,5-heptanedionate) (99.5%, Intatrade, Anhalt-Bitterfeld Germany), Zn(OAc)2 (99.9%, Alpha Aesar, Thermo Fisher GmbH, Germany), and trimethylaluminum (TMA, Al(CH3)3) (98%, Strem Chemicals UK Ltd., Cambridge, UK) were used as precursors for yttrium, europium, zinc and aluminum, respectively, while H2O and/or O3 were used as oxygen precursors for the Y2O3, Al2O3, and Eu2O3 processes. H2S was used as sulfur precursor for the ZnS process. In all processes, N2 was used as a carrier and purging gas. Details about the pulsing sequences and pulse and purge times are presented in Table 1. The doping level of the Y2O3 films with Eu was controlled by pulsing M number of Y2O3 cycles followed by N number of Eu2O3 cycles, resulting in an M:N doping ratio. To form the Y2O3:Eu layer, M:N cycles were repeated until achieving the expected thickness, always starting with a Y2O3 cycle and ending with a Eu2O3 cycle.
The electroluminescent device was prepared using the structure proposed by T. Suyama et al. [19]. The multilayer structure was grown by ALD on a standard glass substrate coated with an ion-diffusion barrier and an ITO layer provided by LUMINEQ (Beneq Oy, Espoo, Finland). First, a 150 nm thick Al2O3 dielectric layer was grown by ALD. It was then followed by several ZnS (50 nm)/Y2O3:Eu (40 nm) multilayers. Finally, another 150 nm thick Al2O3 layer was deposited on the structure. The 1720 nm thick device was finalized by depositing a top contact. A schematic illustration of the device is presented in Figure 1. While it is possible to use a transparent top contact for a fully transparent device, for merely convenience purposes, top contact stripes of aluminum were sputtered here using a mechanical mask. The crossing of the ITO transparent contact and the aluminum stripes, which also comprises the sandwich multilayer Al2O3/ZnS/Y2O3:Eu/Al2O3 structure, creates a passive matrix with a pixel size of 3 × 5 mm2. Note that prior to the deposition of the top Al2O3 layer, the multilayer sequence was always completed with a ZnS top layer.
A SE400adv ellipsometer (SENTECH Instruments GmbH, Berlin, Germany) using a 633 nm wavelength at 70° angle of incidence, was used to determine the growth per cycle (GPC) for each material. GPC values were subsequently used to determine the thickness of the different layers. The crystallinity of Y2O3:Eu and ZnS thin films was investigated by X-ray diffraction (XRD) using the Cu Kα line in a Rigaku SmartLab (Rigaku Europe SE, Neu-Isenburg, Germany) high-resolution X-ray diffractometer equipped with in-plane arm. The XRD data were analyzed using the HighScore Plus 4.6 (PANalytical B.V., Almelo, The Netherlands). Photoluminescence (PL) emission was measured from Y2O3:Eu thin film phosphors with a Hitachi F-7100 Fluorescence Spectrophotometer (Hitachi High-Tech Analytical Science Ltd., Abingdon, UK) equipped with a 150 W xenon lamp. Measurements were performed at room temperature with an excitation slit of 5 nm, emission slit of 2.5 nm, and a photomultiplier tube voltage of 400 V. To determine the excitation wavelength, excitation spectra were recorded for maximum emission at 612 nm. Electroluminescent devices were powered by a Hewlett Packard 6811a source using AC mode at a frequency of 1 kHz. Electroluminescence spectra were recorded using a Konica Minolta CS-2000 spectrometer (Konica Minolta Sensing Europe B.V., Nieuwegein, The Netherlands) with a measurement angle of 1°.
For the calculation of the EL device efficiency, the Sawyer–Tower circuit was used to determine the charge density versus voltage (Q–V) characteristic. The used circuit is composed of a sense capacitor connected in series with the EL device. The total capacitance of the circuit was determined using a Fluke 76 digital multimeter. Data from the Q–V plot were acquired by measuring the voltage at each of the device terminals using a WaveSurfer 3104z (Teledyne Lecroy, Teledyne GmbH, Heidelberg, Germany) oscilloscope. The charge (Q) of the device could be determined by multiplying the output voltage by the total capacitance of the circuit [32]. Simulations were performed using LTspice XVII.

3. Results

To optimize the emission of the Eu-doped Y2O3 thin film phosphors, films with three different Y2O3:Eu2O3 ratios were grown. Thus, three Eu doping concentrations (2:2, 3:2, and 4:2) were obtained by changing the number of Y2O3 and Eu2O3 sequences. As an example, a 4:2 doping configuration refers to a Y2O3:Eu thin film layer in which 4 layers of Y2O3 (Y(MeCp)3/N2/H2O/N2) were followed by 2 layers of Eu2O3 (Eu(Thd)3/N2/O3/N2/H2O/N2) during the ALD process. Taking into consideration Y2O3 and Eu2O3 densities, growth rates on Si substrate, and assuming that the Y2O3 and Eu2O3 films are stoichiometric, the 2:2, 3:2 and 4:2 doping configurations lead to calculated Eu concentrations of 16, 11, and 9 mol%, respectively.

3.1. Characterization of Y2O3:Eu and ZnS Thin Films

Figure 2a shows excitation spectra for a maximum emission at 612 nm, measured between 200 and 450 nm on a Y2O3:Eu sample grown on Si with a Y2O3:Eu2O3 layer ratio of 2:2. The excitation spectrum between 200 and 315 nm was measured using a Hitachi L-39 (UV-39) cutoff filter to remove a high intensity Rayleigh scattering peak located between 288 and 315 nm. The spectra show that the highest emission at 612 nm is obtained for an excitation of 238 nm. Figure 2b shows emission spectra for Y2O3:Eu2O3 layer ratios of 2:2, 3:2, and 4:2. The emission spectra were recorded for the excitation wavelength of 238 nm which was deduced from the excitation spectrum in Figure 2a. All PL spectra show an emission between 575 and 650 nm with a sharp line located at 612 nm. This red color emission is typical of the Eu3+ 5D0 → 7FJ (J = 0, 1, 2, 3, and 4) transitions. Note that Y2O3:Eu samples grown with 2:2 and 4:2 doping configurations show much lower emission intensities compared to the sample grown with a doping concentration of 3:2.
Figure 3a shows grazing incidence X-ray diffractograms for Y2O3:Eu and ZnS thin films measured between 15 and 65°. The Y2O3:Eu sample was prepared with a 3:2 (Y2O3:Eu2O3) cycle ratio. The Y2O3:Eu XRD diffractogram shows that the main phase of the film is polycrystalline (randomly orientated) cubic (pattern number 00-041-1105; Ia3) with some traces of monoclinic phase (marked with asterisk). The grazing incidence XRD data of the ZnS sample show clearly that the sample is highly orientated as only the (002) reflection is observed. The wide bump, between 45 and 60°, most likely originates from the substrate.
Further proof of the orientation was obtained by performing an in-plane measurement that probes the crystalline planes perpendicular to the surface normal as shown in Figure 3b. One can see only (hk0) family of planes meaning that (00l) planes are strongly orientated parallel to the surface. On Figure 3c, which shows the 2θ-ω measurement for the ZnS sample, the hump disappears supporting the idea that it was originated from the substrate. The peak at 59.1° reveals the (004) reflection related to the (002) intense reflection.

3.2. Red Electroluminescent Device

Figure 4a shows a photograph of a 3 × 5 mm2 red Y2O3:Eu/ZnS-based EL pixel under a sinusoidal excitation of 1 kHz measured at 280 Vrms. The photograph was taken with a digital camera in automatic mode under normal room lighting. For this pixel, a brightness of 40 cd/m2 was measured. Figure 4b shows the electroluminescence spectrum, at maximum luminance, of the Y2O3:Eu/ZnS EL device with a 3:2 (Y2O3:Eu2O3) cycle ratio. The EL spectrum, which was measured under an operating voltage of 280 Vmrs and a frequency of 1 kHz, clearly shows the typical 5D0 → 7FJ (J = 0, 1, 2, 3, and 4) transitions in Eu3+ emission centers. The sharp 5D0 → 7F2 line is located at 612 nm. Note the prominent 5D0 → 7F4 emission at 708 nm. The 1931 CIE color coordinates shown in Figure 4c were deduced from the EL spectrum in Figure 4b using OriginLab Chromaticity Diagram script (Origin Pro 2019, Northampton, MA, USA). Thus, the obtained red color emission corresponds to (x, y) values of (0.640, 0.348).
Figure 5a shows the luminance versus applied voltage characteristics of the Y2O3:Eu/ZnS electroluminescent device under a sinusoidal excitation of 1 kHz. The device shows a maximum brightness of 40 cd/m2 at 280 Vrms. The threshold voltage of the device is not well-defined; it can, however, be considered as the voltage needed for the generation of 1 cd/m2 [32]. Here, a luminance of 1 cd/m2 is achieved for an excitation voltage of 180 Vrms. Figure 5b shows Q–V characteristics of a ZnS/Y2O3:Eu EL device, measured at 40 Vrms above the threshold voltage and 1 kHz sinusoidal wave. The measured sense capacitor and total capacitance of the circuit were 171 nF and 6.24 nF, respectively. The input power density, which was calculated by multiplying the area of the graphic in Figure 5b to the applied frequency, was determined to be 153 W/m2. Based on these values, an efficiency of 0.28 Lm/W was calculated. Note the Y axis of the Q–V curve which is not centered in the position (0, 0) coordinates of the graphic.

4. Discussion

Y2O3:Eu, ZnS, and Al2O3 thin films were successfully grown by ALD at 300 °C using commercial precursors. The processing temperature was limited to 300 °C because of the decomposition temperature of the metalorganic precursors and O3. Y2O3:Eu thin film samples, grown with different Eu concentrations, show clearly red emission with a maximum intensity at 612 nm. This line is related to the 5D0 → 7F1 magnetic dipole transition of Eu3+ [34]. With the process conditions described in this work, the optimum Eu concentration was found to be about 11 mol%. While a lower Eu concentration of 9 mol% led to lower PL intensities as expected, the well-known quenching that arises from energy transfer between the Eu3+ luminescent centers was observed for a Eu concentration of 16 mol%. These values are close to the ones reported by H. Huang et al. [35] in comparison with the optimum Eu concentration values of 20 and 5 mol% reported by J. Kaszewski et al. [25] and Y. Kumar et al. [27], respectively.
In a classic DSD electroluminescent device structure, an ideal phosphor should have a polycrystalline structure [32]. Therefore, the polycrystalline nature of our ALD Y2O3:Eu and ZnS thin film layers is advantageous to the multilayer Y2O3:Eu/ZnS electroluminescent device. Furthermore, in comparison with other reported Y2O3:Eu electroluminescent devices [36,37,38], our low processing temperature of 300 °C offers the possibility of building devices on some temperature-resistant polymer flexible substrates [39].
An all-in-one growth step for the Al2O3 dielectric, ZnS, and Y2O3:Eu phosphor layers was used for the fabrication of our EL device by ALD. In contrast to the photoluminescence spectrum, the electroluminescence spectrum shows a prominent 5D0 → 7F4 emission at 708 nm. This could be due to the lower sensitivity of the PL equipment in comparison with the EL equipment, since most photomultiplier tubes have lower sensitivity in the 5D0 → 7F4 transition region [34]. At 280 Vrms and under a sinusoidal excitation of 1 kHz, with the growth conditions reported in this paper, we achieved high-purity red color emission with an intensity up to 40 cd/m2. This intensity could be significantly increased by further optimization of the different device layers, i.e., optimization of Y2O3:Eu and ZnS thicknesses and the dielectric layer (here a mere Al2O3 layer was used). Using multilayer structures, red and green Y2O3/Y2O2S-based electroluminescent devices with luminance up to 137 cd/m2 (at 150 Vrms) and 124 cd/m2 (at 300 Vrms), respectively, were reported by T. Suyama et al. [19] and K. Ohmi et al. [20]. While those values are higher than the ones we obtained for our devices, devices in [19,20] were measured under an excitation frequency of 5 kHz. Frequency has been reported to significantly influence the electroluminescence emission intensity. As an example, luminance values could be increased from 15 to 350 cd/m2 in CaYS:Eu electroluminescent devices by increasing the frequency from 50 Hz to 1 kHz [7].
While it is difficult to compare the efficiency of our device with other red electroluminescent devices due to different measurement conditions, the calculated efficiency of 0.28 Lm/W for our ZnS/Y2O3:Eu multilayer EL device is lower than the 0.8 Lm/W value reported for the ZnS:Mn EL device with red filter and measured with a frequency of 60 Hz [16]. Q–V characteristics usually appear in a trapezoid shape where physical quantities such as threshold voltage, threshold voltage of the phosphor layer, threshold charge density, and transferred charge density are well-defined [32]. The elliptic shape of our Q–V characteristics is due to the multilayer structure of the ZnS/Y2O3:Eu EL device and possible presence of leakage current in the phosphor layer. Our Q–V curve appears negatively biased when the ITO layer of the EL device is connected to the power supply and the top contact is connected to the sense capacitor in the Sawyer–Tower circuit, as shown in Figure 6a. However, when the connections are inverted (the top contact is connected to the power supply and the ITO layer is connected to the sense capacitor), the Q–V curve appears positively biased. Therefore, one possible explanation for this behavior is the asymmetric structure of the device. During the growth process, each phosphor layer starts with the deposition of Y2O3 and finishes with Eu2O3 making ZnS surrounded on one side by Y2O3 and on the other by Eu2O3 as shown in Figure 6a. We believe this asymmetry might favor charge accumulation.
The Q–V characteristics could be reproduced by simulating the equivalent circuit (Figure 6b) of the EL device in the Sawyer–Tower circuit. Figure 6c shows the simulation results of two different scenarios: (i) in red, where the Sawyer–Tower circuit has the EL device with the ITO layer connected to the power supply and the top contact connected to the sense capacitor, as depicted in Figure 6a; and (ii) in blue, where the data were simulated with the top contact connected to the power supply and the ITO layer to the sense capacitor. This simulation requires high voltages and one Zener diode (related to the ZnS/Y2O3 or Eu2O3/ZnS interfaces) with higher threshold voltage than its counterpart. The simulation in Figure 6c matches Figure 5b when the Zener diode DZnS/Y2O3, which is related to the ZnS/Y2O3 interface, has a larger breakdown voltage than DEu2O3/ZnS.

5. Conclusions

In this work, we demonstrate the feasibility of transparent red Y2O3:Eu-based electroluminescent devices by atomic layer deposition at relatively low temperature. Y2O3:Eu, ZnS, and Al2O3 thin films and related multilayer structure devices were prepared at 300 °C. XRD measurements showed high crystallinity of the Y2O3:Eu and ZnS films. Photoluminescence and electroluminescence measurements showed a bright red emission of the phosphors and electroluminescent devices, respectively. A luminance up to 40 cd/m2 and an efficiency of 0.28 Lm/W were achieved. Further optimization of the phosphor and EL device is expected to lead to higher emission intensities.

Author Contributions

Conceptualization, S.M.; formal analysis, J.R., M.J.H., M.S. and S.M.; investigation, J.R., M.J.H., M.S. and S.M.; writing—original draft preparation, J.R. and S.M.; writing—review and editing, J.R. and S.M.; supervision, S.M. All authors have read and agreed to the published version of the manuscript.

Funding

The work in this paper was funded by the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 76495.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data sharing is not applicable to this article.

Acknowledgments

The authors would like to thank Pertti Malvaranta for the preparation of the ITO layer and Elina Haustola for sputtering the top contact.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

References

  1. Leskelä, M.; Mattinen, M.; Ritala, M. Review Article: Atomic layer deposition of optoelectronic materials. J. Vac. Sci. Technol. B 2019, 37, 030801. [Google Scholar] [CrossRef] [Green Version]
  2. Smet, P.F.; Moreels, I.; Hens, Z.; Poelman, D. Luminescence in sulfides: A rich history and a bright future. Materials 2010, 3, 2834–2883. [Google Scholar] [CrossRef] [Green Version]
  3. Wang, L.; Xiao, L.; Gu, H.; Sun, H. Advances in Alternating Current Electroluminescent Devices. Adv. Opt. Mater. 2019, 7, 1–30. [Google Scholar] [CrossRef] [Green Version]
  4. Tanaka, K.; Mikami, A.; Ogura, T.; Taniguchi, K.; Yoshida, M.; Nakajima, S. High brightness red electroluminescence in CaS:Eu thin films. Appl. Phys. Lett. 1986, 48, 1730–1732. [Google Scholar] [CrossRef]
  5. Poelman, D.; Vercaemst, R.; Van Meirhaeghe, R.L.; Laflère, W.H.; Cardon, F. Influence of the growth conditions on the properties of CaS:Eu electroluminescent thin films. J. Lumin. 1997, 75, 175–181. [Google Scholar] [CrossRef]
  6. Abe, Y.; Onisawa, K.I.; Ono, Y.A.; Hanazono, M. Effects of oxygen in CaS:Eu active layers on emission properties of thin film electroluminescent cells. Jpn. J. Appl. Phys. 1990, 29, 1495–1498. [Google Scholar] [CrossRef]
  7. Kawanishi, M.; Miura, N.; Matsumoto, H.; Nakano, R. New red-emitting CaY2S4:Eu thin-film electroluminescent devices. Jpn. J. Appl. Phys. Part 2 Lett. 2003, 42, 10–12. [Google Scholar] [CrossRef]
  8. Koide, T.; Ito, M.; Kawai, T.; Matsushima, Y. An inorganic electroluminescent device using calcium phosphate doped with Eu3+ as the luminescent layer. Mater. Sci. Eng. B Solid-State Mater. Adv. Technol. 2013, 178, 306–310. [Google Scholar] [CrossRef]
  9. Tohda, T.; Fujita, Y.; Matsuoka, T.; Abe, A. New efficient phosphor material ZnS:Sm,P for red electroluminescent devices. Appl. Phys. Lett. 1986, 48, 95–96. [Google Scholar] [CrossRef]
  10. Yin, X.; Wang, S.; Mu, G.; Wan, G.; Huang, M.; Yi, L. Observation of red electroluminescence from an Eu2O3/p + -Si device and improved performance by introducing a Tb2O3 layer. J. Phys. D Appl. Phys. 2017, 50, 105103. [Google Scholar] [CrossRef]
  11. Wellenius, P.; Suresh, A.; Muth, J.F. Bright, low voltage europium doped gallium oxide thin film electroluminescent devices. Appl. Phys. Lett. 2008, 92, 021111. [Google Scholar] [CrossRef]
  12. Wellenius, P.; Suresh, A.; Foreman, J.V.; Everitt, H.O.; Muth, J.F. A visible transparent electroluminescent europium doped gallium oxide device. Mater. Sci. Eng. B Solid-State Mater. Adv. Technol. 2008, 146, 252–255. [Google Scholar] [CrossRef]
  13. Wellenius, P.; Suresh, A.; Luo, H.; Lunardi, L.M.; Muth, J.F. An amorphous indium-gallium-zinc-oxide active matrix electroluminescent pixel. IEEE/OSA J. Disp. Technol. 2009, 5, 438–445. [Google Scholar] [CrossRef]
  14. Wu, X.; Carkner, D. 8.1: Invited Paper: TDEL: Technology Evolution in Inorganic Electroluminescence. SID Symp. Dig. Tech. Pap. 2005, 36, 108. [Google Scholar] [CrossRef]
  15. Ronda, C.R. Recent achievements in research on phosphors for lamps and displays. J. Lumin. 1997, 72–74, 49–54. [Google Scholar] [CrossRef]
  16. Leskelä, M. Rare earths in electroluminescent and field emission display phosphors. J. Alloys Compd. 1998, 275–277, 702–708. [Google Scholar] [CrossRef]
  17. Harazono, T.; Adachi, R.; Shimomura, Y.; Watanabe, T. Firing temperature dependence of Eu diffusion in Eu-Y2O2S studied by 89Y MAS NMR. Phys. Chem. Chem. Phys. 2001, 3, 2943–2948. [Google Scholar] [CrossRef]
  18. Ivanĭ, R.; Novotn, I.; Vlastimil, K. Properties of Y2O3 thin films applicable in Micro–electrochemical Cells. J. Electr. Eng. 2003, 54, 83–87. [Google Scholar]
  19. Suyama, T.; Okamoto, K.; Hamakawa, Y. New type of thin-film electroluminescent device having a multilayer structure. Appl. Phys. Lett. 1982, 41, 462–464. [Google Scholar] [CrossRef]
  20. Ohmi, K.; Tanaka, S.; Kobayashi, H.; Nire, T. Electroluminescent Devices with (Y2O2S:Tb/ZnS) n Multilayered Phosphor Thin Films Prepared by Multisource Deposition. Jpn. J. Appl. Phys. 1992, 31, L1366–L1369. [Google Scholar] [CrossRef]
  21. Adam, J.; Metzger, W.; Koch, M.; Rogin, P.; Coenen, T.; Atchison, J.S.; König, P. Light emission intensities of luminescent Y2O3:Eu and Gd2O3:Eu particles of various sizes. Nanomaterials 2017, 7, 26. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  22. Kostyukov, A.I.; Snytnikov, V.N.; Snytnikov, V.N.; Ishchenko, A.V.; Rakhmanova, M.I.; Molokeev, M.S.; Krylov, A.S.; Aleksandrovsky, A.S. Luminescence of monoclinic Y2O3:Eu nanophosphor produced via laser vaporization. Opt. Mater. 2020, 104, 109843. [Google Scholar] [CrossRef]
  23. Zhu, P.; Wang, W.; Zhu, H.; Vargas, P.; Bont, A. Optical Properties of Eu3+-Doped Y2O3 Nanotubes and Nanosheets Synthesized by Hydrothermal Method. IEEE Photonics J. 2018, 10, 1–10. [Google Scholar] [CrossRef]
  24. Kaszewski, J.; Godlewski, M.M.; Witkowski, B.S.; Słońska, A.; Wolska-Kornio, E.; Wachnicki, Ł.; Przybylińska, H.; Kozankiewicz, B.; Szal, A.; Domino, M.A.; et al. Y2O3:Eu nanocrystals as biomarkers prepared by a microwave hydrothermal method. Opt. Mater. 2016, 59, 157–164. [Google Scholar] [CrossRef]
  25. Kaszewski, J.; Rosowska, J.; Witkowski, B.S.; Wachnicki, Ł.; Wenelska, K.; Mijowska, E.; Bulyk, L.I.; Włodarczyk, D.; Suchocki, A.; Kozankiewicz, B.; et al. Shape control over microwave hydrothermally grown Y2O3:Eu by europium concentration adjustment. J. Rare Earths 2019, 37, 1206–1212. [Google Scholar] [CrossRef]
  26. Li, H.; Kang, J.; Yang, J.; Wu, B. Fabrication of Aunanoparticle@mSiO2@Y2O3:Eu nanocomposites with enhanced fluorescence. J. Alloys Compd. 2016, 673, 283–288. [Google Scholar] [CrossRef]
  27. Kumar, Y.; Pal, M.; Herrera, M.; Mathew, X. Effect of Eu ion incorporation on the emission behavior of Y2O3 nanophosphors: A detailed study of structural and optical properties. Opt. Mater. 2016, 60, 159–168. [Google Scholar] [CrossRef]
  28. De Oliveira Krauser, M.; de Souza Oliveira, H.H.; Cebim, M.A.; Davolos, M.R. Relationship between scintillation properties and crystallite sizes in Y2O3:Eu3+. J. Lumin. 2018, 203, 100–104. [Google Scholar] [CrossRef] [Green Version]
  29. García-Murillo, A.; Carrillo-Romo, F.; de, J.; Oliva-Uc, J.; Esquivel-Castro, T.A.; de la Torre, S.D. Effects of Eu content on the luminescent properties of Y2O3:Eu3+ aerogels and Y(OH)3/Y2O3:Eu3+@SiO2 glassy aerogels. Ceram. Int. 2017, 43, 12196–12204. [Google Scholar] [CrossRef]
  30. Unal, F.; Kaya, F.; Kazmanli, K. Effects of dopant rate and calcination parameters on photoluminescence emission of Y2O3:Eu3+ phosphors: A statistical approach. Ceram. Int. 2019, 45, 17818–17825. [Google Scholar] [CrossRef]
  31. Ali, A.G.; Dejene, B.F.; Swart, H.C. The influence of different species of gases on the luminescent and structural properties of pulsed laser-ablated Y2O2S:Eu3+ thin films. Appl. Phys. A Mater. Sci. Process. 2016, 122, 1–9. [Google Scholar] [CrossRef]
  32. Ono, Y.A. Electroluminescent Displays; Series On Information Display; reprint; World Scientific: Singapore, 1995; ISBN 9810219210. [Google Scholar]
  33. Rosa, J.; Deuermeier, J.; Soininen, P.J.; Bosund, M.; Zhu, Z.; Fortunato, E.; Martins, R.; Sugiyama, M.; Merdes, S. Control of Eu Oxidation State in Y2O3−xSx:Eu Thin-Film Phosphors Prepared by Atomic Layer Deposition: A Structural and Photoluminescence Study. Materials 2019, 13, 93. [Google Scholar] [CrossRef] [Green Version]
  34. Binnemans, K. Interpretation of europium(III) spectra. Coord. Chem. Rev. 2015, 295, 1–45. [Google Scholar] [CrossRef] [Green Version]
  35. Huang, H.; Xu, G.Q.; Chin, W.S.; Gan, L.M.; Chew, C.H. Synthesis and characterization of Eu:Y2O3 nanoparticles. Nanotechnology 2002, 13, 316. [Google Scholar] [CrossRef]
  36. Sowa, K.; Tanabe, M.; Furukawa, S.; Nakanishi, Y.; Hatanaka, Y. Characteristics of Y2O3:Eu/ZnS/Y2O3:Eu Red Light Emitting Elec Fluorescencetroluminescent Devices. Jpn. J. Appl. Phys. 1992, 31, 3598–3602. [Google Scholar] [CrossRef]
  37. Gupta, A.; Brahme, N.; Bisen, D.P. Photoluminescence and Electroluminescence of Eu Doped Y2O3. Phys. Procedia. 2015, 76, 16–24. [Google Scholar] [CrossRef] [Green Version]
  38. Rodionov, V.E.; Shmidko, I.N.; Zolotovsky, A.A.; Kruchinin, S.P. Electroluminescence of Y2O3:Eu and Y2O3:Sm films. Mater. Sci. Pol. 2013, 31, 232–239. [Google Scholar] [CrossRef]
  39. Liu, J.; Ni, H.; Wang, Z.; Yang, S.; Zhou, W. Colorless and Transparent high—Temperature-Resistant Polymer Optical Films—Current Status and Potential Applications in Optoelectronic Fabrications. In Optoelectronics-Materials and Devices; InTech: London, UK, 2015. [Google Scholar]
Materials 14 01505 g001 550
Figure 1. Schematic illustration of the passive matrix-like structure and the device cross section of the Y2O3:Eu/ZnS EL pixel prepared by ALD. The device is based on the multilayer electroluminescent structure proposed by T. Suyama et al. [19]. In this work, 6 layers of Y2O3:Eu and 7 layers of ZnS were used.
Figure 1. Schematic illustration of the passive matrix-like structure and the device cross section of the Y2O3:Eu/ZnS EL pixel prepared by ALD. The device is based on the multilayer electroluminescent structure proposed by T. Suyama et al. [19]. In this work, 6 layers of Y2O3:Eu and 7 layers of ZnS were used.
Materials 14 01505 g001
Materials 14 01505 g002 550
Figure 2. (a) Excitation spectra and (b) emission spectra of ALD Y2O3:Eu thin films prepared with different Eu concentrations. The measurements were performed at room temperature.
Figure 2. (a) Excitation spectra and (b) emission spectra of ALD Y2O3:Eu thin films prepared with different Eu concentrations. The measurements were performed at room temperature.
Materials 14 01505 g002
Materials 14 01505 g003 550
Figure 3. (a) Grazing incidence XRD for Y2O3:Eu and ZnS samples grown by ALD on Si substrates, (*) marks traces of monoclinic phase. The Y2O3:Eu sample was prepared with a 3:2 cycle ratio. (b) XRD spectrum for the ZnS sample measured in in-plane measurement mode. (c) XRD spectrum for the ZnS sample in the 2θ-ω measurement mode.
Figure 3. (a) Grazing incidence XRD for Y2O3:Eu and ZnS samples grown by ALD on Si substrates, (*) marks traces of monoclinic phase. The Y2O3:Eu sample was prepared with a 3:2 cycle ratio. (b) XRD spectrum for the ZnS sample measured in in-plane measurement mode. (c) XRD spectrum for the ZnS sample in the 2θ-ω measurement mode.
Materials 14 01505 g003
Materials 14 01505 g004 550
Figure 4. (a) Photograph of a 3 × 5 mm2 red Y2O3:Eu/ZnS-based EL pixel emitting an intensity of 40 cd/m2. The pixel was measured under normal room lighting. (b) Electroluminescence spectrum of the pixel shown in (a). (c) CIE 1931 chromatography diagram deduced from the spectrum in (b).
Figure 4. (a) Photograph of a 3 × 5 mm2 red Y2O3:Eu/ZnS-based EL pixel emitting an intensity of 40 cd/m2. The pixel was measured under normal room lighting. (b) Electroluminescence spectrum of the pixel shown in (a). (c) CIE 1931 chromatography diagram deduced from the spectrum in (b).
Materials 14 01505 g004
Materials 14 01505 g005 550
Figure 5. (a) Luminance versus the applied voltage and (b) charge–voltage (Q-V) characteristics for the Y2O3:Eu/ZnS electroluminescent device under a sinusoidal wave with a frequency of 1 kHz.
Figure 5. (a) Luminance versus the applied voltage and (b) charge–voltage (Q-V) characteristics for the Y2O3:Eu/ZnS electroluminescent device under a sinusoidal wave with a frequency of 1 kHz.
Materials 14 01505 g005
Materials 14 01505 g006 550
Figure 6. (a) Upside down representation of the 2D schematic of the Y2O3:Eu/ZnS EL device connected in a Sawyer-Tower circuit schematic with an amplification scheme of the ZnS layer and its surroundings. (b) Equivalent circuit of the Y2O3:Eu/ZnS EL device. (c) Simulated Q-V characteristics when (red) ITO is connected to the power supply and the top contact is connected to the sense capacitor; and (blue) ITO is connected to the sense capacitor and the top contact is connected to the power supply.
Figure 6. (a) Upside down representation of the 2D schematic of the Y2O3:Eu/ZnS EL device connected in a Sawyer-Tower circuit schematic with an amplification scheme of the ZnS layer and its surroundings. (b) Equivalent circuit of the Y2O3:Eu/ZnS EL device. (c) Simulated Q-V characteristics when (red) ITO is connected to the power supply and the top contact is connected to the sense capacitor; and (blue) ITO is connected to the sense capacitor and the top contact is connected to the power supply.
Materials 14 01505 g006
Table
Table 1. Pulsing sequences and corresponding pulse time and purge time for the thin films prepared by atomic layer deposition (ALD). Growth per cycle (GPC) values displayed on the table were deduced from ellipsometry measurements.
Table 1. Pulsing sequences and corresponding pulse time and purge time for the thin films prepared by atomic layer deposition (ALD). Growth per cycle (GPC) values displayed on the table were deduced from ellipsometry measurements.
ProcessPulsing SequencePulsing Time (s)GPC [nm]
Y2O3Y(MeCp)3/N2/H2O/N22/6/0.2/70.16
Eu2O3Eu(Thd)3/N2/O3/N2/H2O/N23/7/5/7/0.2/70.03
Al2O3AlMe3/N2/H2O/N20.5/5/0.3/50.10
ZnSZn(OAc)2/N2/H2S/N22.5/6/0.3/30.24
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Rosa, J.; Heikkilä, M.J.; Sirkiä, M.; Merdes, S. Red Y2O3:Eu-Based Electroluminescent Device Prepared by Atomic Layer Deposition for Transparent Display Applications. Materials 2021, 14, 1505. https://doi.org/10.3390/ma14061505

AMA Style

Rosa J, Heikkilä MJ, Sirkiä M, Merdes S. Red Y2O3:Eu-Based Electroluminescent Device Prepared by Atomic Layer Deposition for Transparent Display Applications. Materials. 2021; 14(6):1505. https://doi.org/10.3390/ma14061505

Chicago/Turabian Style

Rosa, José, Mikko J. Heikkilä, Mika Sirkiä, and Saoussen Merdes. 2021. "Red Y2O3:Eu-Based Electroluminescent Device Prepared by Atomic Layer Deposition for Transparent Display Applications" Materials 14, no. 6: 1505. https://doi.org/10.3390/ma14061505

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop