Effect of tin ions on enhancing the intensity of narrow luminescence line at 311 nm of Gd3+ ions in Li2OPbOP2O5 glass system
Introduction
Emission and absorption characteristics of Gd3+ ions in amorphous materials are relatively less investigated when compared with those of other rare earth ions in spite of the fact that these ions give intense UVB emission [1], [2]. Probably, one of the reasons is that the absorption and emission bands of Gd3+ ions lie below the cut off wavelength of several glass hosts. Further, Judd-Ofelt (JO) theory could hardly be applied for Gd3+ ion for the simple reason that the reduced matrix elements of several transitions of this ion are zeros. Because of this reason, Ω4 is indeterminate, whereas Ω2 is found to be erroneous in several cases for this ion [3], [4].
PbO added alkaline/alkaline phosphate glass systems are advantageous for hosting UV luminous ions like Gd3+. PbO makes the glasses more stable against devitrification, increases the moisture resistant capability, density and refractive index of the glass [5], [6], [7]. As a result, the cut-off wavelength of the glass will be lowered significantly and pave the way for observing absorption and emission bands of rare earth ions like Gd3+ in the high energy region. Among all the rare earth ions, it is the Gd3+ ion that gives intense ESR signal at g∼2.0 at room temperature and this signal is attributed to the clusters of gadolinium ions in the glass matrix [8], [9]. By de-clustering (which can be verified by ESR spectra) these ions, the quenching losses due to cross relaxation can be minimized and the intensity of blue emission of Gd3+ ions can be significantly increased. Gd3+ions possess strong excitation band at about 273 nm due to 8S7/2 → 6IJ transitions [10], [11] and gives the emission at 311 nm. This particular beam has got important applications especially in the treatment of vitiligo vulgaris. Several dermatologists have attempted to use this beam in the treatment of such skin diseases [12], [13]. Apart from the aforementioned application to vitiligo the narrowband UVB radiation is most frequently used for the treatment of psoriasis and a wide range of skin diseases, atopic dermatitis, early stages of mycosis fungoides and pruritic disorders.
Interestingly, the semiconducting tin ion (Sn4+ ion) also exhibits emission band at about the same region due to S0 → S2singlet transition [14], [15]. Hence the co-doping of Gd3+ with Sn4+ ions facilitates for the energy transfer between the two ions. In view of this co-doping of Gd3+ with Sn4+is an added advantage for enriching UV emission. Further, it was reported that the tin ions exist in divalent as well as tetravalent states in the glass matrices. The divalent ions were found to be acting as modifiers of the glass network, whereas Sn4+ ions were reported to be participating in network forming [16]. Hence by identifying optimal concentration of tin ions, one can achieve the de-clustering of Gd3+ ions. Thus the admixing of tin ions along with Gd3+ ions to the PbO mixed lithium phosphate glasses, enhances UV emission not only by energy transfer but also by acting as de-clustering agent of Gd3+ ions.
In our earlier studies, we have reported the influence of tin ions on electrical properties of lithium lead phosphate glass system. We have also investigated the enrichment of orange emission of Er3+ ions due to co-doping with Sn4+ ions in the same glass system [17], [18]. Even though some studies are available on emission characteristics of rare earth ions co-doped with Sn4+ ions in alkaline earth glasses like SrOP2O5 [14], Rigorous studies especially de-quenching effects and the application of JO theory to characterize the spectra of Gd3+ ions, are very rare. Motivated by these observations and in view of the important applications of UVB 311 emission in medical therapy, the presented study is devoted to throw some light on the influence of tin ions on the enrichment of UV emission of Gd3+ ions in Li2OPbOP2O5 glass system.
Section snippets
Experimental
The following composition contents (all in mol%) of the glasses are chosen for the present study:S0G0: 20Li2O20PbO60P2O5S0G: 20Li2O20PbO59P2O51.0 Gd2O3S1G: 20Li2O20PbO58P2O51.0 Gd2O3: 1.0 SnO2S3G: 20Li2O20PbO56P2O51.0 Gd2O3: 3.0 SnO2S5G: 20Li2O20PbO54P2O51.0 Gd2O3: 5.0 SnO2S7G: 20Li2O20PbO52P2O51.0 Gd2O3: 7.0 SnO2
The details of preparation of the samples were reported in our earlier papers [17], [18].
Optical absorption spectra of the glasses were recorded in the wavelength region 200–500 nm
Results and discussion
Gd3+ ion concentration Ni and mean Gd3+ion separation ri were evaluated using the measured values of density d and calculated average molecular weight in Li2OPbOP2O5Gd2O3SnO2 glasses and presented in Table 1. Optical absorption spectra (Fig. 1) of glasses co-doped with Gd3+ and Sn4+ ions recorded at ambient temperature in the UV region exhibited several following absorption bands of Gd3+ ions:8S7/2 → 6D9/2, 7/2, 5/2, 6I17/2, 15/2, 13/2, 11/2,9/2,7/2 6P7/2, 5/2.
In addition, the spectra also
Conclusions
Li2OPbOP2O5 glasses doped with 1.0 mol% of Gd2O3 and mixed with different concentrations of SnO2 have been synthesized. The luminescence spectra of the glasses exhibited intense UVB band at about 311 nm due to 6P7/2 → 8S7/2 transition of Gd3+ ion. A significant hike (nearly 4 times) in the intensity of this UVB band is observed when the glasses are mixed with 3.0 mol% of SnO2. The reasons for this enhancement have been have explored in the light of energy transfer from Sn4+ to Gd3+ ions and due
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2022, Materials Chemistry and PhysicsCitation Excerpt :As the concentration of Gd3+ ions increases, the intermolecular distance reduces, and at 5.0 mol%, the Gd3+ ions are so near that there is a strong interaction between two active ions, resulting in the transfer of excitation energy from one Gd3+ ion to another. However, the emission spectra with λex = 275 nm indicate the strongest peak at 614 nm and the emission band excepted the sharp characteristic of Gd3+ ions at 311 nm [21,22]. This data indicated that the emission intensity of Eu2O3 increases with increasing Gd2O3 at 2.5 mol%, this suitable concentration was chosen for further experiments.