Luminescence properties of Sm3+-doped borosilicate glasses

The spectroscopic characterization of borosilicate glasses doped with Sm3+ have been developed by melt quenching technique and investigated by using absorption spectra, excitation spectra, emission spectra and CIE chromaticity diagram analysis. From absorption spectra the most intense and hyper sensitive transition is H5/2 → P3/2 at 403 nm. From photoluminescence emission spectra at excitation wavelength 403 nm, four prominent emission peaks were observed at 563, 600, 647 and 709 nm. For Sm3+ ion the quenching point were observed at 0.5 mol% of borosilicate glasses. The measured color coordinates for the prepared glass matrix fall in the orange region of the CIE diagram.


Introduction
The luminescence properties of the lanthanide ion-doped materials have been hot research topic for decades.The color of the emitted light depends on the lanthanide ion.For instance, Sm 3+ , Dy 3+ and Tb 3+ emit orange, blue and green light, while Pr 3+ ion can emit different colored light depending on the concentration of RE ions as well as surrounding environment [1,2] .This characteristic of lanthanide ions makes it very attractive for synthesizing various kinds of functional materials for application in outdoor devices, fabrication of light emitting diodes, scintillators, lasers, telecommunications, optical fiber cables, solar concentrators, optical detectors such as and the production of wide variety of optical components (as windows, prisms, beam splitters, etc.) [1,3] .Moreover, it has 4 f5 electronic configuration which exhibits orange-red fluorescence in the visible region with strong fluorescence intensity, large emission cross-section and high quantum efficiency.Further, the Sm 3+ ion is well suited to analyze the energy transfer processes, since its emitting 4 G5/2 level has comparatively high quantum efficiency and shows different quenching channels.The luminescence intensity of Sm 3+ ion depends on the concentration of RE ions as well as surrounding environment [4][5][6][7][8] .
The aim of the present work is to develop borosilicate glasses doped with Sm 3+ and investigate their luminescence properties through absorption, photoluminescence (PL) and CIE chromaticity diagram for different application in the solid state lighting field.

Instrumentation and parameters
In the present work, the X-ray diffraction were used to determine amorphous nature of our prepared samples.For the best result the samples were prepared in powder forms and analyzed based on the scattering diffraction of the incident X-ray.A Shimadzu Diffractometer XRD-6100 equipped with diffraction software analysis and provides with Cu radiation was operated at 40kV, 30mA at room temperature.The diffractograms were calibrated to measure in the range of 2ϴ from 10 o to 80 o , in steps of 0.02 o and 1 s counting time per step and speed of 5 o /min.The density of our sample were determined by using Archimedes method Eq. ( 1).Water was selected as an immersive fluid.For all samples, the measurement was done at room temperature and repeated three times to reduce the error.
where Wa and Wb is the weight of glass in air and water, respectively, and ρb is the density of water at room temperature (27 o C), which is 1g/cm 3 .All weight measurements were used a sensitive microbalance.Consequently, the molar volumes of the glass samples were calculated based on the density values according to the following equation: where, Vm is the molar volume, MT is the total molecular weight and ρ is the calculated density of the glass.
The refractive index were measured by using an Abbe refractometer (ATAGO) with a sodium vapor lamp as the light source emitting the light at a wavelength (λ) of 589.3 nm (D line) and having mono-bromonaphthalene as the contact layer between the sample and prism of the refractometer.The visible and near ultraviolet region were determine by using bulk form of the samples.Shimadzu 3600 UV-VIS-NIR spectrophotometer was used in the range of 200-1800 nm to find the absorption spectra of each sample at room temperature.The spectrophotometer results were revealed at the range 200-1800 nm, double monochromatic diffraction grating system and photomultiplier detector with resolution about 0.1 nm.The absorption peaks and band assignments will be obtained from the absorption spectra of each sample.The photo luminescence spectra was determent by using Perkin Elmer LS55 Luminescence Spectrophotometer.The samples were excited with a xenon discharge lamp (200< λ< 300 nm).

Results and discussion
The X-ray diffraction (XRD) pattern of (40-x)SiO2 : 10B2O3: 25Na2O: 8CaO: 5ZrO: 1Bi2O3: 0.5TiO2: 0.5Al2O3: 10BaO: xSm2O3 mol% (where x = 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5 mol% are shown in Figure .2. The XRD spectra show no sharp peak appeared at two theta (2ϴ), which confirmed the amorphous nature of our samples.Figure 3 shows the density values of Sm 3+ -doped borosilicate glasses.The densities decreased from 3.2250 to 3.1048 g/cm 3 with concentration of Sm 3+ ion.The molar volume, on the other hand, show an opposite trend in which increase with concentration of Sm 3+ ion are show in Figure 4. From the results indicate that Sm 3+ ion concentration increases and oxygen packing density decreases.The decreases in oxygen packing density may cause an increase of molar volume, which in turn decreases the mass density of glass samples.The increase in molar volume is due to the increasing of number of non-bridging oxygens (NBOs), which as a result breaks the bonds and loosely packed structure.
Figure 5 shows the variation of refractive index with concentration of Sm 3+ ion in borosilicate glass samples.The refractive index values decrease linearly with concentration of Sm 3+ ion, it is because of the decreasing density of the prepared glass samples.According to the classical dielectric theory, the refractive index depends on density and on polarizability of the atom in a given materials [7] .When the density of the developed glass samples decreases the structure of the glass will be do not compact and velocity of light in this material are not changed which cause the refractive index decreases.The optical absorption spectra of Sm 3+ -doped borosilicate glass measured at room temperature in the ultraviolet-visible (UV-VIS) and near infrared (NIR) regions show in Figure 6.There are eight discrete absorption bands observed due to transitions from the 6 H5/2 level to the various excited states of Sm 3+ ion.The observed absorption bands in the present Sm 3+ -doped borosilicate glass are centered at 403, 479, 942, 1081, 1229, 1377, 1486 and 1534 nm which are assigned to 4 L13/2 + 4 F7/2 + 6 P3/2, 4 I11/2 + 4 M15/2 + 4 I9/2, 6 F11/2, 6 F9/2, 6 F7/2, 6 F5/2, 6 F3/2 and 6 H15/2 energy levels, respectively.These absorption spectra were assigned by comparing the band positions in the absorption spectra with those reported in previous the literature [9] .The transition at 4 L13/2 + 4 F7/2 + 6 P3/2 (403 nm) is the most intense and hyper sensitive absorption transition.

Intensity
For measurement of the luminescence spectra of prepared glass samples it will be important to know the excitation wavelength of the Sm 3+ ions.Figure .7 shows the excitation spectra from 300 to 550 nm for all borosilicate glass doped with Sm 3+ at emission wavelength 600 nm.
From the excitation spectrum, three excitation peaks at wavelength 344, 362, 375, 389, 403, 416, 437, 449, 471, 487, 500 and 528 nm assigned to 4 D7/2+ 4 H9/2, 4 D3/2, 4 D1/2+ 6 P7/2, 4 L15/2, 6 P3/2, 4 M17/2, 4 G9/2, 4 F5/2, 4 I11/2, 4 I9/2, 4 G7/2 and 4 F3/2 respectively [8].From all these transitions, transition at 3 H4→ 3 P2 at wavelength 403 nm has shown the more intensity and has been used as an excitation wavelength for measuring the emission spectra of Sm 3+ -doped borosilicate glasses.The emission spectrum of Sm 3+ -doped borosilicate glass measured at room temperature is shown in Fig. 8.The emission spectra was recorded in the range 500-800 nm, after excitation at wavelength 403 nm.The glass showed orange emission when illuminated by near UV light/black light.The orange emission in the present work results from a mixture of four emissions lines located at 563, 600, 647 and 709 nm, instead of a monochromatic color having a single peak in the spectrum.The emission spectra are contributed from the intra 4f orbitals transition from 4 G5/2 level to the 6 H5/2, 6 H7/2, 6 H9/2 and 6 H11/2 levels of Sm 3+ ion, respectively as shown in Fig. 9 [10][11][12][13] .Out of these emissions, the emission line located at 600 nm ( 4 G5/2→ 6 H7/2) is the most intense.Particularly, the emission lines located at 600, 647 and 709 nm are the most important emissions because these are located at the longer wavelength region of the spectrum.From Fig. 8. it is also observed that emission quenching has been occurred at 0.5 mol% for all the observed bands.The chromaticity diagram of the Commission International del'Eclairage (CIE) indicates that coordinates are highly useful in determining the exact emission color and color purity of a sample.Thus, the CIE chromaticity coordinates for Sm 3+ -doped borosilicate glass were calculated from the PL spectra under 403 nm excitation and marked with a white circle in the CIE 1931 chromaticity diagram in Fig. 10.The chromaticity coordinates (x, y) of these glass samples are located in the orange region.The quality of light emitted is represented by the color correlated temperature (CCT), which is calculated by using McCamy empirical formula and is given by [14] .CCT = -437n 3 + 3601n 2 -6861n + 5514.31 (1) Where, n = (x -xe)/(y-ye) and the chromaticity epicenter is at xe = 0.5952 and ye = 0.4034.

Conclusions
In summary, the Sm 3+ -doped borosilicate glasses have been prepared for different applications in solid state lighting by melt quenching technique and characterized by using absorption, photoluminescence and CIE chromaticity diagram were analyzed.The absorption spectra showed eight absorption band with hypersensitive transition corresponding to 6 P3/2 at 403 nm.The excitation spectra showed that the developed glasses could be effectively excited by UV-light.The emission spectra showed four emission peaks at 563, 600, 647 and 709 nm for borosilicate glasses.From CIE chromaticity diagram the color coordinates of Sm 3+ -doped borosilicate glasses fall in the orange light region.
of the cut and polished prepared glass samples were shown in Figure.1.