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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 16 — Jul. 30, 2012
  • pp: 17701–17710
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High luminescent Li2CaSiO4:Eu2+ cyan phosphor film for wide color gamut field emission display

Xingong Xu, Jun Chen, Shaozhi Deng, Ningsheng Xu, Hongbin Liang, Qiang Su, and Jun Lin  »View Author Affiliations


Optics Express, Vol. 20, Issue 16, pp. 17701-17710 (2012)
http://dx.doi.org/10.1364/OE.20.017701


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Abstract

Li2CaSiO4:Eu2+ cyan phosphor screen for enlarging the color gamut of field emission display has been prepared and characterized. The luminance of Li2CaSiO4:Eu2+ phosphor film can reach as high as about 12000 cd/m2 under the conditions of Va = 7 kV and Ja = 2.8 mA/cm2. The cathodoluminescent spectrum, luminance, saturation current density and degradation property are compared with another cyan phosphor Mg2SnO4:Ti4+,Mn2+. It is found that Li2CaSiO4:Eu2+ phosphor exhibits narrower emission band, higher luminance, higher saturation current density, higher resistance to electron bombardment, higher thermal stability and conductivity as well as purer color. Thus, Li2CaSiO4:Eu2+ has great potential in application in field emission display as well as light emitting diode.

© 2012 OSA

1. Introduction

Field emission display (FED) is a self-emissive display, in which electrons emitted from field emitter arrays excite the phosphor to give off the light. FED has attracted much attention due to its advantages, such as self-emissive display, short response time, distortion-free, high brightness, wide viewing angle, low power consumption, good chromaticity and so on [1

1. N. S. Xu and S. E. Huq, “Novel cold cathode materials and applications,” Mater. Sci. Eng. Rep. 48(2–5), 47–189 (2005). [CrossRef]

5

5. H. S. Jang, J. H. Kang, Y. H. Won, S. Lee, and D. Y. Jeon, “Mechanism for strong yellow emission of Y3Al5O12: Ce3+ phosphor under electron irradiation for the application to field emission backlight units,” Appl. Phys. Lett. 90(7), 071908 (2007). [CrossRef]

]. Development of new high performance phosphor is an important issue for the success of FED. Phosphors for FEDs are required to possess the following properties such as high efficiency under low voltages, high saturation current densities, long lifetime and equal or even better chromaticity than cathode ray tube (CRT) phosphors [6

6. J. H. Hao, J. Gao, and M. Cocivera, “Tuning of the blue emission from europium-doped alkaline earth chloroborate thin films activated in air,” Appl. Phys. Lett. 82(17), 2778–2780 (2003). [CrossRef]

9

9. G. G. Li, X. G. Xu, C. Peng, M. M. Shang, D. L. Geng, Z. Y. Cheng, J. Chen, and J. Lin, “Yellow-emitting NaCaPO4:Mn2+ phosphor for field emission displays,” Opt. Express 19(17), 16423–16431 (2011). [CrossRef] [PubMed]

].

The color gamut is a vital index, which determines the colors the display can present. It depends on the location of the Commission International de l’Eclairage (CIE) coordinates of phosphors, which typically consists of triangle or quadrangle in the CIE diagram. To improve the display quality of full-color displays, such as FEDs as well as light emitting diode (LED) and so on, it is necessary to further enlarge the color gamut of phosphors. One method is to make the color of current commercial phosphors more saturated. Another approach is to develop novel materials, which have CIE coordinates locating outside the triangle of commercial FED tricolor phosphors. Cyan phosphor is considered to be the ideal candidate for this purpose, which can enlarge the color gamut of display and thus improve the display quality [10

10. G. G. Li, X. Zhang, C. Peng, M. M. Shang, D. L. Geng, Z. Y. Cheng, and J. Lin, “Cyan-emitting Ti4+- and Mn2+-coactivated Mg2SnO4 as a potential phosphor to enlarge the color gamut for field emission display,” J. Mater. Chem. 21(18), 6477–6779 (2011). [CrossRef]

,11

11. M. B. Xie, H. B. Liang, Q. Su, Y. Huang, Z. H. Gao, and Y. Tao, “Intense cyan-emitting of Li2CaSiO4:Eu2+ under low-voltage cathode ray excitation,” Electrochem. Solid-State Lett. 14(10), J69–J72 (2011). [CrossRef]

]. Besides, from the CIE chromaticity diagram, one may see clearly that color purity depends on the position of CIE coordinates. For similar colors, the closer to the spectral locus, the higher the color purity is.

To our best knowledge, no results have been reported on the performance of cyan phosphor film in a field emission device. It is known that the morphology of phosphor particle as well as fabrication procedure of phosphor screen may also affect the characteristics of the phosphors and sometimes the luminous efficiency may decrease dramatically [25

25. X. G. Xu, J. Chen, S. Z. Deng, N. S. Xu, and J. Lin, “Cathodoluminescent properties of nanocrystalline Lu3Ga5O12:Tb3+ phosphor for field emission display application,” J. Vac. Sci. Technol. B 28(3), 490–494 (2010). [CrossRef]

27

27. L. E. Shea, “Low-voltage cathodoluminescent phosphors,” Electrochem. Soc. Interface 7(2), 24–27 (1998).

]. Thus, it is important and necessary to study further the luminescent properties of these phosphor film. Moreover, there is still no report on how efficient the cyan phosphor materials, and on their purity. Such data are necessary for consideration for commercial use. In this study, a higher efficient, purer cyan-emitting LCSO:Eu2+ phosphor screen have been prepared and characterized. The CL properties, the luminance as a function of anode current densities under different anode voltages and degradation properties of LCSO:Eu2+ phosphor screen will be presented. Comparison of its performance with Mg2SnO4:Ti4+,Mn2+ cyan phosphor screen has also been carried out.

2. Experimental

Preparation. LCSO:Eu2+ phosphor powder was synthesized by high temperature solid state reaction method [11

11. M. B. Xie, H. B. Liang, Q. Su, Y. Huang, Z. H. Gao, and Y. Tao, “Intense cyan-emitting of Li2CaSiO4:Eu2+ under low-voltage cathode ray excitation,” Electrochem. Solid-State Lett. 14(10), J69–J72 (2011). [CrossRef]

]. The starting materials Li2CO3 (A.R.), CaCO3 (A.R.), SiO2 (A.R.), and Eu2O3 (99.99%) were weighed stoichiometrically and grounded thoroughly in an agate mortar and pestle. Then the mixture were heated at 1073 K for 6 h under a reductive atmosphere (N2/H2 = 3:1). The final products were cooled down to room temperature (RT) and grounded again. The optimum doping concentration of Eu2+ is about 0.9%, which substitutes for the Ca2+ due to similar ionic radii (Eu2+: 0.098 nm, and Ca2+: 0.100 nm).

Characterization. Phosphor screen was prepared on indium-tin-oxide (ITO) glass by screen printing method following the procedure for fabricating a FED phosphor screen. Phosphor slurry was screen printed onto ITO glass and sintered at 450 °C for 1 hour under ambient atmosphere to burn out the residual organic binder. The details of the process can be found in an early literature [25

25. X. G. Xu, J. Chen, S. Z. Deng, N. S. Xu, and J. Lin, “Cathodoluminescent properties of nanocrystalline Lu3Ga5O12:Tb3+ phosphor for field emission display application,” J. Vac. Sci. Technol. B 28(3), 490–494 (2010). [CrossRef]

]. Multiple printing process was used to improve the packing densities of phosphor layer. The thickness of the printed phosphor layer was about 24 μm, which was measured by a surface profiler (Dektak 150).

The morphology of phosphor layer was observed by a scanning electron microscope (SEM) and the composition and crystal structure were measured using Rigaku D/max-IIIA x-ray diffractometer with Cu Kα radiation (λ = 1.54056 Å). The cathodoluminescent measurement of both LCSO:Eu2+ and Mg2SnO4:Ti4+,Mn2+ phosphor screen was carried out in a vacuum chamber with a pressure below 2 × 10−4 Pa. The phosphor screen is assembled with a gated CNT cold cathode to form a triode field emission display device. The samples were heated at 100 °C for 30 min to remove the absorbed moisture before they were put into the vacuum chamber. The CL spectra and the CL intensities were measured with an spectrometer (Ocean Optics QEB1004 Platinum). A luminance meter (Konica-Minolta LS110) recorded the luminance transmitted through the phosphor layer on the ITO substrate, which faced directly to the front of phosphor screen. The voltage applied to the phosphor screen was changed from 1 kV to 7 kV, and the excitation anode current density was in the range from 0 mA/cm2 to 4.5 mA/cm2. Decay time curves as well as temperature dependence of emission spectra for LCSO:Eu2+ phosphor were acquired using a time-correlated single photon counting spectrometer with a 450 W nanosecond flash lamp (nF900; channels: 1000; pulse frequency: 40 kHz). While for Mg2SnO4:Ti4+,Mn2+ phosphor, a 60 W microsecond flash lamp was introduced (μF900; channels: 2000; pulse frequency: 50 Hz). We used a tungsten microprobe installed inside a SEM system to measure the electrical characteristics of the phosphor. The microprobe was pressed on the surface of a single phosphor particle. Positive and negative biases were applied to the microprobe and current-voltage (I-V) characteristics were recorded using a Keithley 6487 pico-ammeter. The I-V characteristics of these two phosphors were measured from three randomly chosen particles.

3. Results and discussion

We used the vacuum light emitting tube as a device for the following measurements. Its electron source used our patented design [28

28. N. S. Xu, J. C. She, S. Z. Deng, and J. Chen, “A gun with a cold cathode,” EP Patent 1,508,910 (2008).

] and the performance of lighting emitting tubes using carbon nanotube as cold cathode was reported early [29

29. J. Chen, X. H. Liang, S. Z. Deng, and N. S. Xu, “Flat-panel luminescent lamp using carbon nanotube cathodes,” J. Vac. Sci. Technol. B 21(4), 1727–1729 (2003). [CrossRef]

]. Firstly, both LCSO:Eu2+ and Mg2SnO4:Ti4+,Mn2+ cyan phosphor screens were prepared on ITO substrate by screen printing method. Then, CL properties of both phosphor screens were measured in a vacuum chamber (<2x10−4 Pa) with the bombardment of electron beams from the electron source using a gated carbon nanotube cold cathode.

Figure 1(a)
Fig. 1 (a) SEM image of cross-section view of Li2CaSiO4:Eu2+ phosphor layer prepared on ITO glass substrate. (b) Typical XRD pattern of Li2CaSiO4:Eu2+ phosphor layer.
shows the SEM image of cross-section review of LCSO:Eu2+ phosphor screen prepared on ITO glass. The SEM image shows clearly that the sample is composed of phosphor particles with size distribution ranging within 3 to 8 μm. The film looks compact, since there are few hollows between phosphor particles. The thickness is estimated to be about 24 μm, which is in accordance with the result from surface profiler.

Figure 1(b) shows the structure and phase purity of the prepared LCSO:Eu2+ phosphor screen. The diffraction peaks match well with the standard data of Li2CaSiO4 (JCPDS 27-0290) with two main peaks. The doped Eu2+ does not change the XRD pattern. The prominent peak (112) locates at 37.58° belonging to tetragonal structure and the second peak (110) lies at 25.09 o. The FWHM of (112) and (110) peak are 0.176 and 0.146, respectively. The lattice constant (d value) of (112) and (110) in our experiment are calculated to be 2.39 Å and 3.55 Å, while the theoretical d-value of these two peaks are 2.40 Å and 3.58 Å, respectively. The lattice parameters are a = b = 5.047 Å, c = 6.486 Å, and the space group is I4¯2m. The experimental results are almost identical with the theoretical results, and this implies that the degree of crystallization is good during the phosphor powder synthesis procedure under the circumstance of a relatively lower sintering temperature (800 °C) by solid state reaction method. Besides, a second phase locating at 29.503 o is observed, which we are not sure how exactly it comes from. But after comparing CL spectrum below (Fig. 2(a)
Fig. 2 (a) Typical CL spectrum of Li2CaSiO4:Eu2+ phosphor screen measured under Va = 7 kV and Ja = 50 μA/cm2. Top left inset shows the luminescent image of the phosphor screen during CL measurement and top right inset shows the amplified CL spectrum from 550 nm to 780 nm. (b) Integrated CL intensity for Li2CaSiO4:Eu2+ and Mg2SnO4:Ti4+,Mn2+ phosphors as a function of anode voltage; Top left inset shows the calculated electron penetration depth for both phosphors.
) with early result [11

11. M. B. Xie, H. B. Liang, Q. Su, Y. Huang, Z. H. Gao, and Y. Tao, “Intense cyan-emitting of Li2CaSiO4:Eu2+ under low-voltage cathode ray excitation,” Electrochem. Solid-State Lett. 14(10), J69–J72 (2011). [CrossRef]

], we could conclude that this does not have any influence on the emission and therefore it could be neglectable.

The CL spectrum of LCSO:Eu2+ phosphor screen is shown in Fig. 2(a). It consists of one dominant emission band locating at 480 nm and four weaker emission bands (594 nm, 618 nm, 653 nm and 702 nm, see the inset of Fig. 2(a) at top left). The peak at 480 nm is attributed to 4f65d1→4f7 transition of Eu2+ with FWHM of only 37 nm, which is much narrower than most phosphors doped with Eu2+. Smaller FWHM is considered to be beneficial for obtaining higher luminous output due to more integral overlap with eye sensitivity curve [19

19. J. Liu, J. Y. Sun, and C. S. Shi, “A new luminescent material: Li2CaSiO4:Eu2+,” Mater. Lett. 60(23), 2830–2833 (2006). [CrossRef]

,30

30. T. Jüstel, H. Nikol, and C. Ronda, “New developments in the field of luminescent materials for lighting and displays,” Angew. Chem. Int. Ed. 37(22), 3084–3103 (1998). [CrossRef]

]. The CIE coordinates of single emission peak is more saturated than that of another cyan phosphor, i.e. Mg2SnO4:Ti4+,Mn2+, whose spectrum consists of two emission peaks and has a wider FWHM. The four weaker emission peaks are considered to be due to the 5D07FJ (J = 1,2,3,4) transitions of Eu3+. This might result from the residual composition Eu2O3 during the mass synthesis procedure and we think that this could be negligible because it possesses only about 2% intensity of the main emission peak as is shown in Fig. 2(a). The luminescent image during CL measurement was recorded and a typical one is shown in the inset (top right) of Fig. 2(a), from which one can observe it emits intense cyan light.

A schematic diagram of emission mechanism for LCSO:Eu2+ could be described below. As the primary electrons hit phosphor layer surface, they would induce ionization processes, which in turn generate highly energetic electrons. These energetic electrons can be further multiplied in number through collisions, creating secondary electrons. These secondary electrons can migrate in the solid with high kinetic energy and could excite Eu2+ from 4f ground state to 5d excited state. When it returns to 4f ground state by radiative transition, cyan emission locating at 480 nm would occur. At the same time, this process would be accompanied by 5D07FJ (J = 1, 2, 3, 4) transitions of Eu3+ due to the residual matter during the synthesis process.

Figure 2(b) shows CL intensity of LCSO:Eu2+ phosphors measured under different anode voltages when the anode current density is 50 μA/cm2. The result from Mg2SnO4:Ti4+,Mn2+ is also shown for comparison. The CL intensities of both LCSO:Eu2+ and Mg2SnO4:Ti4+,Mn2+ phosphors increase with anode voltages. The CL integrated intensity of LCSO:Eu2+ is much larger than that of Mg2SnO4:Ti4+,Mn2+ under same anode voltage. The ratio of CL integrated intensity between LCSO:Eu2+ and Mg2SnO4:Ti4+,Mn2+ phosphor screens increases with anode voltages. For instance, the ratios are 1.2, 1.9, 2.9, 3.6, 4.6 and 5.5 under the bombardment of electron beams of 2 keV, 3 keV, 4 keV, 5 keV, 6 keV and 7 keV, respectively. To find the physical origin, we make the following analysis.

We calculate the electron penetration depth (L(Å)) for both LCSO:Eu2+ and Mg2SnO4:Ti4+,Mn2+ phosphors using the following empirical Eq.:

L[Å]=250(Aρ)(EZ)n,n=1.210.29lgZ

Where A is the atomic or molecular weight of the material, ρ is the bulk density, Z is the atomic number or the number of electrons per molecule in the compounds, and E is the accelerating voltage (kV) [31

31. C. Feldman, “Range of 1-10 kev electrons in solids,” Phys. Rev. 117(2), 455–459 (1960). [CrossRef]

]. The results are shown in the top left inset of Fig. 2(b). For LCSO:Eu2+, ρ = 2.90 g/cm3, Z = 72, A = 146.00, thus the estimated electron penetration depths at 1 kV, 3 kV, 5 kV and 7 kV are 4.8 nm, 84.2 nm, 318.0 nm, 763.0 nm, respectively. The electron penetration depths for Mg2SnO4:Ti4+,Mn2+ were also estimated and shown in the inset (top left) of Fig. 2(b). For Mg2SnO4:Ti4+,Mn2+, ρ = 4.77 g/cm3, Z = 106, A = 231.33, thus the estimated electron penetration depths at 1 keV, 3 keV, 5 keV and 7 keV are 1.4 nm, 33.6 nm, 148.5 nm, 395.0 nm, respectively. As the anode voltage increases, the penetrations of electron beam into both phosphor layers increase too, so more light would be emitted for both phosphor layers.

The results in the inset (top left) of Fig. 2(b) also show that the electron penetration depth of LCSO:Eu2+ is larger than that of Mg2SnO4:Ti4+,Mn2+. To improve the electron penetration depth, phosphor materials with lower ρ and Z are preferred [12

12. P. H. Holloway, T. A. Trottier, B. Abrams, C. Kondoleon, S. L. Jones, J. S. Sebastian, W. J. Thomes, and H. Swart, “Advances in field emission displays phosphors,” J. Vac. Sci. Technol. B 17(2), 758–764 (1999). [CrossRef]

]. The ρ and Z value for LCSO:Eu2+ are lower than that of Mg2SnO4:Ti4+,Mn2+. This is the reason to the larger electron penetration depth of LCSO:Eu2+ phosphor. Also, with the increase of anode voltage, the difference on electron penetration depth between LCSO:Eu2+ and Mg2SnO4:Ti4+,Mn2+ increases too. For example, differences on electron penetration depth are 3.4 nm, 50.6 nm, 169.5 nm and 368.0 nm when the anode voltage is 1 kV, 3 kV, 5 kV and 7 kV, respectively. The larger electron penetration depth is one reason for the better CL performance of LCSO:Eu2+.

Figure 3(a)
Fig. 3 (a) Luminance of Li2CaSiO4:Eu2+ phosphor screen as a function of anode current density under different anode accelerating voltages. (b) Luminance of Mg2SnO4:Ti4+,Mn2+ phosphor screen under 7 kV; (c) Decay time for Li2CaSiO4:Eu2+. (d) Decay time for Mg2SnO4:Ti4+,Mn2+.
shows the average luminance as a function of anode current densities for LCSO:Eu2+ phosphor screen under different anode voltages. The luminance of LCSO:Eu2+ phosphor screen increased with the anode current densities, luminance saturation phenomenon was observed only when anode current density went to as high as 2.8 mA/cm2. The highest luminance could reach 12000 cd/m2 under Va = 7 kV and Ja = 2.8 mA/cm2. The highest luminance at 5 kV is about 4800 cd/m2 (3 mA/cm2), which shows LCSO:Eu2+ phosphor has good luminance even under relatively low excitation voltage. For comparison, we also measured the luminescent property of Mg2SnO4:Ti4+,Mn2+ phosphor screen under the bombardment of electron beams of 7 keV, as shown in Fig. 3(b). The luminance of Mg2SnO4:Ti4+,Mn2+ phosphor screen begins to saturate when the current density is above 1.25 mA/cm2 under Va = 7 kV. This indicates that LCSO:Eu2+ phosphor possesses much higher saturation current density than that of Mg2SnO4:Ti4+,Mn2+ phosphor, that is 2.8 mA/cm2 to 1.25 mA/cm2 under Va = 7 kV. Under the condition of Va = 7 kV and Ja = 1.25 mA/cm2, the luminance for Mg2SnO4:Ti4+,Mn2+ phosphor screen is only about 650 cd/m2 while the luminance for LCSO:Eu2+ phosphor screen can be 9 times higher, i.e. 6000 cd/m2. This means that LCSO:Eu2+ phosphor is more efficient than Mg2SnO4:Ti4+,Mn2+ phosphor.

Shorter decay time is much helpful to increase saturation current density of phosphor due to more activator recycling frequency according to some researchers’ results [12

12. P. H. Holloway, T. A. Trottier, B. Abrams, C. Kondoleon, S. L. Jones, J. S. Sebastian, W. J. Thomes, and H. Swart, “Advances in field emission displays phosphors,” J. Vac. Sci. Technol. B 17(2), 758–764 (1999). [CrossRef]

,32

32. C. Stoffers, S. Yang, F. Zhang, S. M. Jacobsen, B. K. Wagner, and C. J. Summers, “Activator recycling in low voltage cathodoluminescent phosphors,” Appl. Phys. Lett. 71(13), 1759 (1997). [CrossRef]

34

34. C. Stoffers, S. Yang, S. M. Jacobsen, and C. J. Summers, “Saturation of phosphors under low-voltage excitation,” J. Soc. Inf. Disp. 4(4), 337 (1996). [CrossRef]

]. To find physical reasons responsible for higher saturation current density in LCSO:Eu2+ phosphor, we measured decay time of both phosphors. And we found that LCSO:Eu2+ phosphor possesses much shorter decay time than that of Mg2SnO4:Ti4+,Mn2+ phosphor. The decay time of LCSO:Eu2+ and Mg2SnO4:Ti4+,Mn2+ is 429 ns and 6.54 μs, respectively as Fig. 3(c) and Fig. 3(d) show. Our results match well with the theoretical one. Thus, we could propose that high saturation current density in LCSO:Eu2+ is mainly due to the shorter decay time observed. Therefore, the LCSO:Eu2+ cyan phosphor is more efficient and more suitable for high energy device application.

The aging properties for both LCSO:Eu2+ and Mg2SnO4:Ti4+,Mn2+ were also measured and the results are shown in Fig. 4
Fig. 4 Comparison of the degradation properties of Li2CaSiO4:Eu2+, Mg2SnO4:Ti4+,Mn2+ and ZnS: Ag, Cl phosphor screen under constant electron bombardment (Va = 7 kV and Ja = 50 μA/cm2).
. The measurement was carried out under the condition of anode voltage of 7 kV and anode current density of 50 μA/cm2. Figure 4 gives the normalized CL peak intensities of these two phosphor screens as a function of bombardment time. It could be seen that LCSO:Eu2+ has a slower decay rate than Mg2SnO4:Ti4+,Mn2+. After being bombarded by persistent electron beam for 2.5 hours, LCSO:Eu2+ could retain about 64.7% of the initial intensity, while Mg2SnO4:Ti4+,Mn2+ could only keep about 48.6% of the initial value. For contrast, the result of degradation for commercial blue phosphor ZnS: Ag, Cl (IRICO Group Corp.) was also presented in Fig. 4 which was measured under the same condition and 40% of the initial intensity was retained. The better degradation properties of LCSO:Eu2+ is apparently due to the stable nature of oxide host. Therefore a long lifetime is expected for LCSO:Eu2+ when applied in FED.

To find the intrinsic reason responsible for better degradation property of LCSO:Eu2+ phosphor, we measured photoluminescence emission spectra for both phosphors under different temperature ranging from 25 °C to 200 °C which is close to temperature range in the application of FED device as well as LED device. Figure 5(a)
Fig. 5 Comparison of the emission spectra for (a) Mg2SnO4:Ti4+,Mn2+ and (b) Li2CaSiO4:Eu2+ as well as (c) dependence of the integral emission intensity on temperature for both phosphors.
and Fig. 5(b) show the emission spectra of both LCSO:Eu2+ and Mg2SnO4:Ti4+,Mn2+ phosphors under 288 nm and 244 nm excitation, respectively. One could see clearly that FWHM of both LCSO:Eu2+ and Mg2SnO4:Ti4+,Mn2+ phosphors increase with the temperature rising, which is attributed to the population of higher vibration levels, the density of phonons, and the probability of non-radiative transfer (energy migration to defects) brought by the increasing temperature [35

35. D. Y. Wang, C. H. Huang, Y. C. Wu, and T. M. Chen, “BaZrSi3O9:Eu2+: a cyan-emitting phosphor with high quantum efficiency for white light-emitting diodes,” J. Mater. Chem. 21(29), 10818–10822 (2011). [CrossRef]

,36

36. W. Im, S. Brinkley, J. Hu, A. Mikhailovsky, S. DenBaars, and R. Seshadri, “Sr2. 975− xBaxCe0. 025AlO4F: a highly efficient green-emitting oxyfluoride phosphor for solid state white lighting,” Chem. Mater. 22(9), 2842–2849 (2010). [CrossRef]

].

Figure 5(c) represents the dependence of the integral emission intensity on temperature for both phosphor screens. The emission intensity of both LCSO:Eu2+ and Mg2SnO4:Ti4+,Mn2+ phosphor gradually decrease with the increase of temperature due to the thermal quenching effect as shown in Fig. 5(c). Furthermore, when the temperature rises up from 25 °C to 200 °C, Mg2SnO4:Ti4+,Mn2+ phosphor could only maintain about 35% of the initial value, while LCSO:Eu2+ phosphor could keep above 60% of the initial value. Namely, the former one suffers a more serious thermal quenching, and this could be the main reason for the better stability for LCSO:Eu2+ phosphor. In both FED and LED devices, thermal quenching is a vital factor to succeed commercial products with longer lifetime. So in this case, LCSO:Eu2+ phosphor is still more advantageous than that of Mg2SnO4:Ti4+,Mn2+ phosphor in the application of FED and LED.

Besides, we carried out electrical conductivity measurement on these two phosphors to further understand the reason of higher saturation current density and better degradation property observed from LCSO:Eu2+ phosphor screen. The inset of Fig. 6(a)
Fig. 6 I-V characteristics measured from (a) Li2CaSiO4:Eu2+ and (b) Mg2SnO4:Ti4+,Mn2+ phosphor particles using a microprobe. Bottom right inset shows one SEM picture of the microprobe on a Li2CaSiO4:Eu2+ phosphor particle.
shows the set-up of using a microprobe to measure the electrical properties of a phosphor particle. From the I-V characteristics in Fig. 6, we observed that the resistance of LCSO:Eu2+ is much lower than that of Mg2SnO4:Ti4+,Mn2+. For example, when the voltage reached 300 V, the current was about 2 pA for LCSO:Eu2+ phosphor as shown in Fig. 6(a), while it was only about 1 pA for Mg2SnO4:Ti4+,Mn2+ phosphor as Fig. 6(b) shows. From the linear part of the I-V curve, we calculated the effective resistance to be 1.5 × 108 MΩ for LCSO:Eu2+ and 3 × 108 MΩ for Mg2SnO4:Ti4+,Mn2+. Namely, the resistance of Mg2SnO4:Ti4+,Mn2+ is higher than that of LCSO:Eu2+. Thus, when the electrons bombard the phosphor, the charge-up phenomenon is more liable to happen for the phosphor with higher resistance. Therefore, we would expect high saturation current density from phosphor with high conductivity. This is in accord with the results we observed from LCSO:Eu2+ phosphor.

The CIE coordinates of LCSO:Eu2+ phosphor are calculated to be x = 0.108, y = 0.200. The CIE coordinates are shown in Fig. 7(a)
Fig. 7 (a) CIE coordinates of Li2CaSiO4:Eu2+ phosphor in a CIE 1931 chromaticity diagram together with CIE coordinates of CRT and FED tricolor phosphors. (b) CIE coordinates comparison in FED tricolor phosphors for both Li2CaSiO4:Eu2+ and Mg2SnO4:Ti4+,Mn2+ phosphor.
, which locates outside the color gamut triangle of CRT (Y2O3:Eu, ZnS:Cu,Al, ZnS:Ag,Cl) and FED tricolor (Y2O3:Eu, Y2SiO5:Tb, Y2SiO5:Ce) phosphors. The area of color gamut after the introduction of LCSO:Eu2+ phosphor is calculated to be 17.6% larger than that of CRT tricolor and 30.1% larger than that of FED tricolor [12

12. P. H. Holloway, T. A. Trottier, B. Abrams, C. Kondoleon, S. L. Jones, J. S. Sebastian, W. J. Thomes, and H. Swart, “Advances in field emission displays phosphors,” J. Vac. Sci. Technol. B 17(2), 758–764 (1999). [CrossRef]

]. While for Mg2SnO4:Ti4+,Mn2+ cyan phosphor, the CIE coordinates are x = 0.146, y = 0.287. The increase of the area of color gamut is about 14.3% larger than that of CRT tricolor and 27.9% larger than that of FED tricolor [12

12. P. H. Holloway, T. A. Trottier, B. Abrams, C. Kondoleon, S. L. Jones, J. S. Sebastian, W. J. Thomes, and H. Swart, “Advances in field emission displays phosphors,” J. Vac. Sci. Technol. B 17(2), 758–764 (1999). [CrossRef]

]. Besides, from Fig. 7(b), we could see clearly that CIE coordinates of LCSO:Eu2+ phosphor is much closer to the spectral locus than that of Mg2SnO4:Ti4+,Mn2+ phosphor, therefore, we could expect higher color purity in LCSO:Eu2+ phosphor. It is obvious that LCSO:Eu2+ phosphor is so far the best cyan phosphor for achieving the goal of widening color gamut of FED display.

4. Conclusion

The performance of LCSO:Eu2+ cyan-emitting phosphor was characterized under conditions similar to FED device. High luminance (about 12000 cd/m2 under Va = 7 kV and Ja = 2.8 mA/cm2) was obtained. Higher saturation current density for LCSO:Eu2+ phosphor is obtained due to its shorter decay time than that of Mg2SnO4:Ti4+,Mn2+. Better luminescent performance as well as better stability property from LCSO:Eu2+ phosphor was observed compared with Mg2SnO4:Ti4+,Mn2+. One main reason for better stability property of LCSO:Eu2+ phosphor is due to less thermal quenching according to our experimental result. Another one is its higher conductivity. CIE coordinates of LCSO:Eu2+ phosphor show that it has purer color and that it can widen the color gamut of FED display. Due to its excellent characteristics, LCSO:Eu2+ phosphor is a most promising candidate for four-color FEDs.

Acknowledgments

The authors gratefully acknowledge the financial support of the project from the National Natural Science Foundation of China (Grant No. U0634002, 60925001), Science and Technology Ministry of China (Grant No. 2010CB327703, 2007CB935501), FANEDD (Grant No. 200727), the Science and Technology Department of Guangdong Province, the Economic and Information Industry Commission of Guangdong Province, and the Science & Technology and Information Department of Guangzhou City, and supported by the Fundamental Research Funds for the Central Universities.

References and links

1.

N. S. Xu and S. E. Huq, “Novel cold cathode materials and applications,” Mater. Sci. Eng. Rep. 48(2–5), 47–189 (2005). [CrossRef]

2.

B. F. Coll, K. A. Dean, E. Howard, S. V. Johnson, M. R. Johnson, and J. E. Jaskie, “Nano-emissive display technology for large-area HDTV,” J. Soc. Inf. Disp. 14(5), 477–485 (2006). [CrossRef]

3.

A. A. Talin, K. A. Dean, and J. E. Jaskie, “Field emission displays: a critical review,” Solid-State Electron. 45(6), 963–976 (2001). [CrossRef]

4.

H. J. Jeong, H. D. Jeong, H. Y. Kim, J. S. Kim, S. Y. Jeong, J. T. Han, D. S. Bang, and G. W. Lee, “All-carbon nanotube-based flexible field-emission devices: from cathode to anode,” Adv. Funct. Mater. 21(8), 1526–1532 (2011). [CrossRef]

5.

H. S. Jang, J. H. Kang, Y. H. Won, S. Lee, and D. Y. Jeon, “Mechanism for strong yellow emission of Y3Al5O12: Ce3+ phosphor under electron irradiation for the application to field emission backlight units,” Appl. Phys. Lett. 90(7), 071908 (2007). [CrossRef]

6.

J. H. Hao, J. Gao, and M. Cocivera, “Tuning of the blue emission from europium-doped alkaline earth chloroborate thin films activated in air,” Appl. Phys. Lett. 82(17), 2778–2780 (2003). [CrossRef]

7.

N. Hirosaki, R. J. Xie, K. Inoue, T. Sekiguchi, B. Dierre, and K. Tamura, “Blue-emitting AlN:Eu2+ nitride phosphor for field emission displays,” Appl. Phys. Lett. 91(6), 061101 (2007). [CrossRef]

8.

X. M. Liu and J. Lin, “Nanocrystalline LaGaO3: Tm as an efficient blue phosphor for field emission displays with high color purity,” Appl. Phys. Lett. 90(18), 184108 (2007). [CrossRef]

9.

G. G. Li, X. G. Xu, C. Peng, M. M. Shang, D. L. Geng, Z. Y. Cheng, J. Chen, and J. Lin, “Yellow-emitting NaCaPO4:Mn2+ phosphor for field emission displays,” Opt. Express 19(17), 16423–16431 (2011). [CrossRef] [PubMed]

10.

G. G. Li, X. Zhang, C. Peng, M. M. Shang, D. L. Geng, Z. Y. Cheng, and J. Lin, “Cyan-emitting Ti4+- and Mn2+-coactivated Mg2SnO4 as a potential phosphor to enlarge the color gamut for field emission display,” J. Mater. Chem. 21(18), 6477–6779 (2011). [CrossRef]

11.

M. B. Xie, H. B. Liang, Q. Su, Y. Huang, Z. H. Gao, and Y. Tao, “Intense cyan-emitting of Li2CaSiO4:Eu2+ under low-voltage cathode ray excitation,” Electrochem. Solid-State Lett. 14(10), J69–J72 (2011). [CrossRef]

12.

P. H. Holloway, T. A. Trottier, B. Abrams, C. Kondoleon, S. L. Jones, J. S. Sebastian, W. J. Thomes, and H. Swart, “Advances in field emission displays phosphors,” J. Vac. Sci. Technol. B 17(2), 758–764 (1999). [CrossRef]

13.

K. S. Sohn, J. H. Kwak, Y. S. Jung, H. X. Yan, and M. J. Reece, “Luminescence of Sr2SiO4-xN2x/3:Eu2+ phosphors prepared by spark plasma sintering,” J. Electrochem. Soc. 155(2), J58–J61 (2008). [CrossRef]

14.

S. H. Yang and M. Yokoyama, “Enhanced luminance of ZnGa2O4 phosphor by In2O3 doping,” J. Vac. Sci. Technol. A 19(5), 2463–2467 (2001). [CrossRef]

15.

E. Coetsee, H. C. Swart, and J. J. Terblans, “Cathodoluminescence degradation of Y2SiO5: Ce thin films,” J. Vac. Sci. Technol. A 25(4), 1226–1230 (2007). [CrossRef]

16.

S. S. Pitale, V. Kumar, I. M. Nagpure, O. M. Ntwaeaborwa, E. Coetsee, and H. C. Swart, “Cathodoluminescent properties and surface characterization of bluish-white LiAl5O8:Tb phosphor,” J. Appl. Phys. 109(1), 013105 (2011). [CrossRef]

17.

A. R. Lakshmanan, S. B. Kim, H. M. Jang, B. G. Kum, B. K. Kang, S. Heo, and D. Seo, “A quantum-splitting phosphor exploiting the energy transfer from anion excitons to Tb3+ in CaSO4: Tb, Na,” Adv. Funct. Mater. 17(2), 212–218 (2007). [CrossRef]

18.

P. Dorenbos, L. Pierron, L. Dinca, C. W. E. van Eijk, A. Kahn-Harari, and B. Viana, “4f-5d spectroscopy of Ce3+ in CaBPO5, LiCaPO4 and Li2CaSiO4,” J. Phys. Condens. Matter 15(3), 511–520 (2003). [CrossRef]

19.

J. Liu, J. Y. Sun, and C. S. Shi, “A new luminescent material: Li2CaSiO4:Eu2+,” Mater. Lett. 60(23), 2830–2833 (2006). [CrossRef]

20.

K. Toda, Y. Kawakami, S. Kousaka, Y. Ito, A. Komeno, K. Uematsu, and M. Sato, “New silicate phosphors for a white LED,” IEICE Trans. Electron. E 89-C(10), 1406–1412 (2006).

21.

M. Saradhi and U. V. Varadaraju, “Photoluminescence studies on Eu2+-activated Li2SrSiO4: a potential orange-yellow phosphor for solid-state lighting,” Chem. Mater. 18(22), 5267–5272 (2006). [CrossRef]

22.

S. S. Yao and D. H. Chen, “Combustion synthesis and luminescent properties of a new material Li2(Ba0.99,Eu0.01)SiO4:B3+ for ultraviolet light emitting diodes,” Opt. Laser Technol. 40(3), 466–471 (2008). [CrossRef]

23.

C. Kulshreshtha, N. Shin, and K. S. Sohn, “Decay behavior of Li2(Sr,Ba,Ca)SiO4:Eu2+ Phosphors,” Electrochem. Solid-State Lett. 12(6), J55–J57 (2009). [CrossRef]

24.

C. Kulshreshtha, A. K. Sharma, and K. S. Sohn, “Effect of local structures on the luminescence of Li2(Sr,Ca,Ba)SiO4:Eu2+,” J. Electrochem. Soc. 156(3), J52–J56 (2009). [CrossRef]

25.

X. G. Xu, J. Chen, S. Z. Deng, N. S. Xu, and J. Lin, “Cathodoluminescent properties of nanocrystalline Lu3Ga5O12:Tb3+ phosphor for field emission display application,” J. Vac. Sci. Technol. B 28(3), 490–494 (2010). [CrossRef]

26.

E. T. Goldburt, V. A. Bolchouchine, B. N. Levonovitch, and N. P. Sochtine, “Highly efficient cathodoluminescent phosphors and screens for mid- and high-voltage field emission displays,” J. Vac. Sci. Technol. B 17(2), 765–768 (1999). [CrossRef]

27.

L. E. Shea, “Low-voltage cathodoluminescent phosphors,” Electrochem. Soc. Interface 7(2), 24–27 (1998).

28.

N. S. Xu, J. C. She, S. Z. Deng, and J. Chen, “A gun with a cold cathode,” EP Patent 1,508,910 (2008).

29.

J. Chen, X. H. Liang, S. Z. Deng, and N. S. Xu, “Flat-panel luminescent lamp using carbon nanotube cathodes,” J. Vac. Sci. Technol. B 21(4), 1727–1729 (2003). [CrossRef]

30.

T. Jüstel, H. Nikol, and C. Ronda, “New developments in the field of luminescent materials for lighting and displays,” Angew. Chem. Int. Ed. 37(22), 3084–3103 (1998). [CrossRef]

31.

C. Feldman, “Range of 1-10 kev electrons in solids,” Phys. Rev. 117(2), 455–459 (1960). [CrossRef]

32.

C. Stoffers, S. Yang, F. Zhang, S. M. Jacobsen, B. K. Wagner, and C. J. Summers, “Activator recycling in low voltage cathodoluminescent phosphors,” Appl. Phys. Lett. 71(13), 1759 (1997). [CrossRef]

33.

S. M. Jacobsen, “Phosphors for full-color low-voltage field-emission displays,” J. Soc. Inf. Disp. 4(4), 331 (1996). [CrossRef]

34.

C. Stoffers, S. Yang, S. M. Jacobsen, and C. J. Summers, “Saturation of phosphors under low-voltage excitation,” J. Soc. Inf. Disp. 4(4), 337 (1996). [CrossRef]

35.

D. Y. Wang, C. H. Huang, Y. C. Wu, and T. M. Chen, “BaZrSi3O9:Eu2+: a cyan-emitting phosphor with high quantum efficiency for white light-emitting diodes,” J. Mater. Chem. 21(29), 10818–10822 (2011). [CrossRef]

36.

W. Im, S. Brinkley, J. Hu, A. Mikhailovsky, S. DenBaars, and R. Seshadri, “Sr2. 975− xBaxCe0. 025AlO4F: a highly efficient green-emitting oxyfluoride phosphor for solid state white lighting,” Chem. Mater. 22(9), 2842–2849 (2010). [CrossRef]

OCIS Codes
(160.4670) Materials : Optical materials
(160.4760) Materials : Optical properties
(250.1500) Optoelectronics : Cathodoluminescence
(300.6280) Spectroscopy : Spectroscopy, fluorescence and luminescence

ToC Category:
Materials

History
Original Manuscript: May 22, 2012
Revised Manuscript: July 3, 2012
Manuscript Accepted: July 4, 2012
Published: July 19, 2012

Virtual Issues
Vol. 7, Iss. 9 Virtual Journal for Biomedical Optics

Citation
Xingong Xu, Jun Chen, Shaozhi Deng, Ningsheng Xu, Hongbin Liang, Qiang Su, and Jun Lin, "High luminescent Li2CaSiO4:Eu2+ cyan phosphor film for wide color gamut field emission display," Opt. Express 20, 17701-17710 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-16-17701


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References

  1. N. S. Xu and S. E. Huq, “Novel cold cathode materials and applications,” Mater. Sci. Eng. Rep.48(2–5), 47–189 (2005). [CrossRef]
  2. B. F. Coll, K. A. Dean, E. Howard, S. V. Johnson, M. R. Johnson, and J. E. Jaskie, “Nano-emissive display technology for large-area HDTV,” J. Soc. Inf. Disp.14(5), 477–485 (2006). [CrossRef]
  3. A. A. Talin, K. A. Dean, and J. E. Jaskie, “Field emission displays: a critical review,” Solid-State Electron.45(6), 963–976 (2001). [CrossRef]
  4. H. J. Jeong, H. D. Jeong, H. Y. Kim, J. S. Kim, S. Y. Jeong, J. T. Han, D. S. Bang, and G. W. Lee, “All-carbon nanotube-based flexible field-emission devices: from cathode to anode,” Adv. Funct. Mater.21(8), 1526–1532 (2011). [CrossRef]
  5. H. S. Jang, J. H. Kang, Y. H. Won, S. Lee, and D. Y. Jeon, “Mechanism for strong yellow emission of Y3Al5O12: Ce3+ phosphor under electron irradiation for the application to field emission backlight units,” Appl. Phys. Lett.90(7), 071908 (2007). [CrossRef]
  6. J. H. Hao, J. Gao, and M. Cocivera, “Tuning of the blue emission from europium-doped alkaline earth chloroborate thin films activated in air,” Appl. Phys. Lett.82(17), 2778–2780 (2003). [CrossRef]
  7. N. Hirosaki, R. J. Xie, K. Inoue, T. Sekiguchi, B. Dierre, and K. Tamura, “Blue-emitting AlN:Eu2+ nitride phosphor for field emission displays,” Appl. Phys. Lett.91(6), 061101 (2007). [CrossRef]
  8. X. M. Liu and J. Lin, “Nanocrystalline LaGaO3: Tm as an efficient blue phosphor for field emission displays with high color purity,” Appl. Phys. Lett.90(18), 184108 (2007). [CrossRef]
  9. G. G. Li, X. G. Xu, C. Peng, M. M. Shang, D. L. Geng, Z. Y. Cheng, J. Chen, and J. Lin, “Yellow-emitting NaCaPO4:Mn2+ phosphor for field emission displays,” Opt. Express19(17), 16423–16431 (2011). [CrossRef] [PubMed]
  10. G. G. Li, X. Zhang, C. Peng, M. M. Shang, D. L. Geng, Z. Y. Cheng, and J. Lin, “Cyan-emitting Ti4+- and Mn2+-coactivated Mg2SnO4 as a potential phosphor to enlarge the color gamut for field emission display,” J. Mater. Chem.21(18), 6477–6779 (2011). [CrossRef]
  11. M. B. Xie, H. B. Liang, Q. Su, Y. Huang, Z. H. Gao, and Y. Tao, “Intense cyan-emitting of Li2CaSiO4:Eu2+ under low-voltage cathode ray excitation,” Electrochem. Solid-State Lett.14(10), J69–J72 (2011). [CrossRef]
  12. P. H. Holloway, T. A. Trottier, B. Abrams, C. Kondoleon, S. L. Jones, J. S. Sebastian, W. J. Thomes, and H. Swart, “Advances in field emission displays phosphors,” J. Vac. Sci. Technol. B17(2), 758–764 (1999). [CrossRef]
  13. K. S. Sohn, J. H. Kwak, Y. S. Jung, H. X. Yan, and M. J. Reece, “Luminescence of Sr2SiO4-xN2x/3:Eu2+ phosphors prepared by spark plasma sintering,” J. Electrochem. Soc.155(2), J58–J61 (2008). [CrossRef]
  14. S. H. Yang and M. Yokoyama, “Enhanced luminance of ZnGa2O4 phosphor by In2O3 doping,” J. Vac. Sci. Technol. A19(5), 2463–2467 (2001). [CrossRef]
  15. E. Coetsee, H. C. Swart, and J. J. Terblans, “Cathodoluminescence degradation of Y2SiO5: Ce thin films,” J. Vac. Sci. Technol. A25(4), 1226–1230 (2007). [CrossRef]
  16. S. S. Pitale, V. Kumar, I. M. Nagpure, O. M. Ntwaeaborwa, E. Coetsee, and H. C. Swart, “Cathodoluminescent properties and surface characterization of bluish-white LiAl5O8:Tb phosphor,” J. Appl. Phys.109(1), 013105 (2011). [CrossRef]
  17. A. R. Lakshmanan, S. B. Kim, H. M. Jang, B. G. Kum, B. K. Kang, S. Heo, and D. Seo, “A quantum-splitting phosphor exploiting the energy transfer from anion excitons to Tb3+ in CaSO4: Tb, Na,” Adv. Funct. Mater.17(2), 212–218 (2007). [CrossRef]
  18. P. Dorenbos, L. Pierron, L. Dinca, C. W. E. van Eijk, A. Kahn-Harari, and B. Viana, “4f-5d spectroscopy of Ce3+ in CaBPO5, LiCaPO4 and Li2CaSiO4,” J. Phys. Condens. Matter15(3), 511–520 (2003). [CrossRef]
  19. J. Liu, J. Y. Sun, and C. S. Shi, “A new luminescent material: Li2CaSiO4:Eu2+,” Mater. Lett.60(23), 2830–2833 (2006). [CrossRef]
  20. K. Toda, Y. Kawakami, S. Kousaka, Y. Ito, A. Komeno, K. Uematsu, and M. Sato, “New silicate phosphors for a white LED,” IEICE Trans. Electron.E 89-C(10), 1406–1412 (2006).
  21. M. Saradhi and U. V. Varadaraju, “Photoluminescence studies on Eu2+-activated Li2SrSiO4: a potential orange-yellow phosphor for solid-state lighting,” Chem. Mater.18(22), 5267–5272 (2006). [CrossRef]
  22. S. S. Yao and D. H. Chen, “Combustion synthesis and luminescent properties of a new material Li2(Ba0.99,Eu0.01)SiO4:B3+ for ultraviolet light emitting diodes,” Opt. Laser Technol.40(3), 466–471 (2008). [CrossRef]
  23. C. Kulshreshtha, N. Shin, and K. S. Sohn, “Decay behavior of Li2(Sr,Ba,Ca)SiO4:Eu2+ Phosphors,” Electrochem. Solid-State Lett.12(6), J55–J57 (2009). [CrossRef]
  24. C. Kulshreshtha, A. K. Sharma, and K. S. Sohn, “Effect of local structures on the luminescence of Li2(Sr,Ca,Ba)SiO4:Eu2+,” J. Electrochem. Soc.156(3), J52–J56 (2009). [CrossRef]
  25. X. G. Xu, J. Chen, S. Z. Deng, N. S. Xu, and J. Lin, “Cathodoluminescent properties of nanocrystalline Lu3Ga5O12:Tb3+ phosphor for field emission display application,” J. Vac. Sci. Technol. B28(3), 490–494 (2010). [CrossRef]
  26. E. T. Goldburt, V. A. Bolchouchine, B. N. Levonovitch, and N. P. Sochtine, “Highly efficient cathodoluminescent phosphors and screens for mid- and high-voltage field emission displays,” J. Vac. Sci. Technol. B17(2), 765–768 (1999). [CrossRef]
  27. L. E. Shea, “Low-voltage cathodoluminescent phosphors,” Electrochem. Soc. Interface7(2), 24–27 (1998).
  28. N. S. Xu, J. C. She, S. Z. Deng, and J. Chen, “A gun with a cold cathode,” EP Patent 1,508,910 (2008).
  29. J. Chen, X. H. Liang, S. Z. Deng, and N. S. Xu, “Flat-panel luminescent lamp using carbon nanotube cathodes,” J. Vac. Sci. Technol. B21(4), 1727–1729 (2003). [CrossRef]
  30. T. Jüstel, H. Nikol, and C. Ronda, “New developments in the field of luminescent materials for lighting and displays,” Angew. Chem. Int. Ed.37(22), 3084–3103 (1998). [CrossRef]
  31. C. Feldman, “Range of 1-10 kev electrons in solids,” Phys. Rev.117(2), 455–459 (1960). [CrossRef]
  32. C. Stoffers, S. Yang, F. Zhang, S. M. Jacobsen, B. K. Wagner, and C. J. Summers, “Activator recycling in low voltage cathodoluminescent phosphors,” Appl. Phys. Lett.71(13), 1759 (1997). [CrossRef]
  33. S. M. Jacobsen, “Phosphors for full-color low-voltage field-emission displays,” J. Soc. Inf. Disp.4(4), 331 (1996). [CrossRef]
  34. C. Stoffers, S. Yang, S. M. Jacobsen, and C. J. Summers, “Saturation of phosphors under low-voltage excitation,” J. Soc. Inf. Disp.4(4), 337 (1996). [CrossRef]
  35. D. Y. Wang, C. H. Huang, Y. C. Wu, and T. M. Chen, “BaZrSi3O9:Eu2+: a cyan-emitting phosphor with high quantum efficiency for white light-emitting diodes,” J. Mater. Chem.21(29), 10818–10822 (2011). [CrossRef]
  36. W. Im, S. Brinkley, J. Hu, A. Mikhailovsky, S. DenBaars, and R. Seshadri, “Sr2. 975− xBaxCe0. 025AlO4F: a highly efficient green-emitting oxyfluoride phosphor for solid state white lighting,” Chem. Mater.22(9), 2842–2849 (2010). [CrossRef]

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