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Strong Upconversion Emission of Erbium Doped Oxyfluoride Tellurite Glasses: Role of Erbium Contents
S.K. Md Zain1,a, M.R. Sahar2,b* and E.S. Sazali3,c
1,2,3
Advanced Optical Material Research Group, Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia
a[email protected],*b[email protected], c[email protected]
Abstract: Recently, many researchers have been attracted to erbium doped oxyfluoride glass, especially owing to their excellent properties in upconvension emission radiation for a large variety of optical applications. In this study, series of erbium doped zirconium oxyfluoride tellurite glass of composition (88.5-z) TeO2 - 10MgO - (z)ZrF4 - 1.5Er2O3 (0 ≤ z ≤ 4 mol%) were prepared using melt quenching technique and their physical and photoluminesence characteristics are investigated. The presence of a broad hump and absence of sharp peak in X-ray diffraction (XRD) pattern confirms the amorphous nature of glass The glass density and molar volume are found in the range of 4.52-5.03 g/cm3 and 30.29-33.48 cm3/mol, respectively. The zirconium oxyfluoride tellurite glass contains 1.5 mol% Er2O3 shows the highest enhancement in the emission transition of 4S3/2→4I15/2. The result of the present work revealed that the investigated glass can be a potential material for photonic devices and solid state lasers.
Keywords: Tellurite glass, Oxyflouride, melt quenching, photoluminescence, emission Recently, the upconversion of visible light by various rare earth doped glass ions have widely been studied due to their capability in the field of photonics [1]. The well-chosen of glass host is very important to gain a better environment for rare earth (RE) as a medium of photonic application. Therefore, the combination of low phonon energies of tellurite glass host with good spectroscopic properties of fluoride material might resulting to an excellent formation of the local bonding environment of oxide and fluoride around the rare-earth ions [2]. Among the rare earth ions, Er3+ gets more attention probably due to its energy level structure that is suitable for application in solid-state lasers and optical amplifiers [3][4].
Previous studies reported that a low phonon glasses doped with Er3+ shows an intense NIR and visible up-conversion emission radiations [5]. It has also been reported that the multicomponent tellurite glass has successfully produced an upconversion emission at the excitation wavelengths of 378 and 976 nm with a variation of erbium concentration [6].
However, the PL intensity exhibits a quenching behavior beyond a critical erbium concentration of 0.5 mol% . By the presence of ZrF4 in Er3+ doped oxyfluoride-tellurite glass, it is expected that a better environment due to the low phonon energy of ZrF4 and erbium will exhibit an enhancement behavior in the upconversion emission radiations.
Melt-quenching technique was used to prepared a batch of erbium doped zirconium oxyfluoride tellurite glasses with different composition of Er2O3 (0.0, 0.5, 1.0, 1.5, and 2.0 mol%). 15 g of the batch was weighed and mixed by milling machine before being placed in an alumina crucible and melted in a furnace at 1000oC. After 1 hour, the melt is quenched on a stainless steel plat mold before being annealed at 300oC for 3 hours. Rigaku SmartLab High Resolution X-Ray Diffractometer with a radiation source of Cukα and wavelength of 1.54056 Å (40kV and 100mA) was used to obtain the X-ray diffraction pattern. The luminescence spectra was characterized under the excitation at 980nm.
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Figure 1 shows a typical XRD pattern for zirconium oxyfluoride tellurite glass doped with 1.5 mol % of erbium. The present of broad hump without any sharp peak confirms the characteristic of amorphousity of the sample [7]
0 10 20 30 40 50 60 70 80 90 2 q
Coun ts ( arb.u nits)
Figure 1: A typical X-ray diffraction pattern of sample zirconium oxyfluoride tellurite glass doped with 1.5 mol % of erbium
Figure 2 presents a plot of density and molar volume versus Er2O3 concentration. The glass density and molar volume were found in the range of 4.52-5.03 g/cm3 and 30.29-33.48 cm3/mol, respectively. Initially, at the substitution of Er2O3 up to 1.5 mole%, it is observed that the density decreases slightly from 4.91 to 4.52 g/cm3. This might be due to the addition of Er2O3 into the glass network that has triggered some structural rearrangements of the atom in such away that the interatomic spacing inside the glass network is increased [3].. However, the density gradually increases from 4.52 to 5.03 g/cm3 as the Er2O3 is raised up to 2.0 mol%.
This increment might be due to the effective replacement of lower molecular weight of TeO2 (159.6 g/mol) by a higher molecular weight of Er2O3 (382.56 g/mol), which as a result, the density of the glass to be denser [6]. From Figure 2, it is also found that the molar volume exhibits an opposite trend to the density, which is in aggrement with those previously reported [8].
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0.0 0.5 1.0 1.5 2.0
4.4 4.6 4.8 5.0
Er2O3 (mol %) Density (g/cm3 )
29.0 29.5 30.0 30.5 31.0 31.5 32.0 32.5 33.0 33.5 34.0
Molar Volume (cm3 /mol)
Figure 1: The density and molar volume of zirconium oxyfluoride tellurite glasses at different Er2O3 content.
The upconversion (UC) emission spectra of erbium zirconium oxyfluoride tellurite glass in the visible wavelength under 980 nm excitation are shown in Figure 3. From Figure 3, it can clearly be observed that there are two intense green and one red emissions centered at around 525, 554 and 657, which are associated for 2H11/2 →4I15/2 , 4S3/2→4I15/2, and
4F9/2→4I15/2 transition, respectively. It can also be seen that the emission maxima is shifted to the higher wavelength (red shift) with the increase of erbium content. A comparison among the spectra, the UC arises from predominant transition, 4S3/2→4I15/2, and weak transition of
2H11/2 →4I15/2 and 4F9/2→4I15/2. The luminescence intensity of Er3+ band in transition of
4S3/2→4I15/2 is increased by a factor of 2.19 with the addition of 1.5 mol % erbium and decreased in a factor of 0.29 with the addition of 2.0 mol % erbium content. According to Sajna et al., the fluorescence intensity enhancement is highly depending on the spontaneous radiation transition [6]. In this study, 1.5 mol % erbium doped zirconium oxyfluoride tellurite glass with the lowest density and rigidity creates a strong upconversion emission in predominant and weak transition. The addition erbium into the glass, might also lead the energy transfer between erbium ions themselves.
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In conclusion, the introduction of various concentrations of Er2O3 into the glass network, strongly effect on their physical and photoluminescence properties.
Acknowledgement
The authors gratefully acknowledge the financial support from Ministry of Higher Education, Universiti Teknologi Malaysia and Malaysia via Gants of Vot:
4F083,07J80,06J39.
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500 550 600 650 700
0 1x10
62x10
63x10
64x10
65x10
64F9/2 -> 4I15/2
4S3/2 -> 4I15/2
2 H11/2 -> 4 I15/2
0.0 mol% erbium 0.5 mol% erbium 1.0 mol% erbium 1.5 mol% erbium 2.0 mol% erbium
Wavelength(nm)
Lu minesce nce Intensity (a.u .)
Figure 3: The upconversion emission spectra of erbium doped zirconium oxyfluoride tellurite glass upon 980nm excitation.
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