A PHOTOLUMINESCENCE STUDY OF ND 3+ DOPED DIFFERENT CHLORO-PHOSPHATE GLASSES FOR SOLID STATE LASER APPLICATIONS

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1 International Journal of Nanotechnology and Application (IJNA) ISSN(P): ; ISSN(E): Vol. 4, Issue 4, Aug 014, 3-8 TJPRC Pvt. Ltd. A PHOTOLUMINESCENCE STUDY OF ND 3+ DOPED DIFFERENT CHLORO-PHOSPHATE GLASSES FOR SOLID STATE LASER APPLICATIONS K. VENKATA RAO 1 & Y. C. RATNAKARAM 1 Department of Physics, S. B. V. R. Degree College, Badvel, Kadapa, Andhra Pradesh, India Department of Physics, Sri Venkateswara University, Tirupati, Aandhra Pradesh, India ABSTRACT Investigations of glasses as host materials for rare earth fluorescence with potential for laser is confined to borate, phosphate, silicate, tellurite and fluoride glasses. Glass materials are attractive hosts because planer waveguides and optical fibers can be fabricated easily compared to crystalline materials. Absorption and emission spectra of 1mol% of Nd 3+ doped different chlorophosphate glasses have been studied. By applying, Judd-Ofelt theory, three intensity parameters Ω, Ω 4 and Ω 6. These parameters are useful to evaluate the radiative properties such as radiative transition probabilities (A rad ), branching ratios (ß), integrated absorption cross-sections (Σ), radiative lifetimes (τ R ). From emission spectrum, emission cross-sections (σp) is calculated for all chlorophosphate glasses and reported. KEYWORDS: Absorption Spectra, Phosphate Glasses, Emission Spectra, Rare Earth Ions INTRODUCTION Applications in solid-state lasers, integrated optical amplifiers, infrared display devices and up-conversion fibers have stimulated the development of rare earth doped glasses. Among rare-earth ions, neodymium (Nd 3+ ) is one of the most efficient ions for solid-state lasers due to its intense emission at 1060 nm. The Nd 3+ ion has been used in a number of laser systems, due to the relatively wide availability of samples of this ion doped in a range of host materials [1]. So, a primary disadvantage of pure vitreous P O 5 and phosphate glasses is their low chemical stability. Glasses containing more than 50 mol% P O 5 are more vulnerable to hydrolytic action of water than those containing less P O 5. The low chemical durability of phosphate glasses can be improved also by the addition of both network formers and glass modifiers []. In this work, a detailed study of the spectroscopic and laser properties of Nd 3+ doped different phosphate (Na, K,, Ca, Na-K, Na- and Na-Ca) glass matrices. Using Judd-Ofelt theory [3, 4], Judd-Ofelt parameters are calculated in these glass matrices. The radiative properties of 4f-4f transitions in rare-earth ions doped glasses are very important for the characterization of laser properties. The radiative properties such as, total radiative transition probabilities (A T ) and raditive lifetimes (τ R ), branching ratios (ß R ) and integrated absorption cross-sections (Σ) of certain excited sates are estimated. From the emission spectra, peak stimulated emission cross-sections (σ p ) are calculated. Our main interest in the present work is to identify the good transitions for laser excitation. EXPERIMENTAL Rare-earth doped different phosphate glasses were prepared using melt quenching technique method. The chemical compositions: 69 P O 5-0 Na HPO 4-10 R-Cl-1Nd O 3 (R= Na, K, and Ca) and 69 P O 5-0 Na HPO 4-5 NaCl-5 R-Cl-1Nd O 3 (R= K, and Ca) were used for glass preparation. All these chemicals used in the present work are 99.99% purity. The samples were polished to obtain smooth, transparent and uniform surface for optical measurement. editor@tjprc.org

2 4 K. Venkata Rao & Y. C. Ratnakaram Also, physical measurements such as thickness, density and refractive index were carried out. The prepared glasses were polished on both sides to obtain planar surfaces before measuring their optical properties. All these measurements were carried out at room temperature. The amorphous nature of the prepared Nd 3+ doped different phosphate glasses were confirmed through the X-ray diffraction (XRD) studies using on a C 10 diffractometer employing Co Kα radiation. Optical absorption spectra were obtained using JASCO; V-570 UV-VIS-NIR spectrophotometer. Emission spectra of Nd 3+ doped glasses were measured using SPEX Fluorolog- fluorometer under the excitation wavelength, nm using Xe arc lamp (150 W) as the excitation source in the wavelength region nm. RESULTS AND DISCUSSIONS XRD and Absorption Spectra The XRD patterns of Nd 3+ doped different chlorophosphate glass matrices are shown in Figure 1, which is the characteristic feature of structural disorder that confirms the amorphous nature of the prepared glass es under investigation (expect sodium magnesium and sodium calcium). The optical absorption spectra of Nd 3+ doped sodium chlorophosphate glass matrix observed in the wavelength region nm is shown in Figure From the absorption spectra twelve absorption peaks pertaining to, 4 F 5/ + H 9/, 4 F 7/ + 4 S 3/, 4 F 9/, H 11/, 4 G 5/ + G 7/, K 13/ + 4 G 7/, 4 G 9/, K 15/ + G 9/ + D 3/, 4 G 11/, P 1/ and 4 D 3/ + 4 D 5/ with 4 I 9/ as the ground state are observed for all the Nd 3+ doped different chlorophosphate glass matrices expect for sodium calcium chloro phosphate glass matrix ( 4 D 3/ + 4 D 5/ transition is not observed in this glass matrix). Though the observed spectra appear similar for all the glass matrices, the spectral intensities and spectral profiles of certain transitions vary from one glass matrix to another glass matrix. In the present work, the spectral profile of the transition 4 D 3/ + 4 D 5/ clearly indicates such variation for different glass matrices. Spectral Intensities and Judd-Ofelt Parameters The measured spectral intensities and calculated spectral intensities for all the spectral intensities of different absorption bands of Nd 3+ ions calculated. It is observed that among four chlorophosphate glass matrices potassium glass matrix showing higher spectral intensities. Among the three mixed chlorophosphat e glass matrix sodium potassium glass showing higher spectral intensity values. The best set Judd-Ofelt intensity parameters [3, 4], Ω, Ω 4, Ω 6, and ΣΩ parameters are presented in Table 1. The Ω parameter indicates the covalence of the metal-ligand bond, whereas Ω 4 and Ω 6 indicate the rigidity of the host materials. In the calculation of the above intensity parameters, the spectral of transitions P 1/ and 4 D 3/ + 4 D 5/ are not included in the least square fitting procedure because there is some uncertainty in the measurement of the spectral intensities. Due to overlapping of certain absorption peaks, i.e. 4 F 5/ on H 9/, 4 F 7/ on 4 S 3/, 4 G 5/ on G 7/ and K 13/ on 4 G 7/. It is observed that Ω and Ω 6 parameters are more sodium, potassium and sodium potassium chlorophosphate glass matrices when compared with other glass matrices. It indicates more covlance of Nd-O bond in these glass matrices. It is also indicates that crystal field asymmetry at the site of Nd 3+ ion is high for sodium, potassium and sodium potassium chlorophosphate glass matrices. it is also observed that, Ω 4 parameter lower for sodium-potassium glass matrix indicating lower rigidity of the glass matrix. Jacob and Weber introduced new parameter which is called spectroscopic quality factor χ (Ω 4/ Ω 6 ) is presented in table. In the present work, the χ value range for different phosphate matrices. Impact Factor (JCC): Index Copernicus Value (ICV): 3.0

3 A Photoluminescence Study of Nd 3+ Doped Different Chloro-Phosphate Glasses for Solid State Laser Applications 5 Hypersensitive Transitions The spectral intensity of hypersensitive transition is largely dependent on the surrounding environment of Nd 3+ ion and in turn it shows the effect on intensity parameters. For Nd 3+ ion, the hypersensitive transition is 4 I 9/ 4 G 5/. The shift in the peak wavelength of the hypersensitive transition towards longer wavelength indicates increase in the degree of covalency of Nd-O bond. Normally the intensity parameter, indicates covalence decreases/increases with the decrease/increase of intensity of the hypersensitive transition. There is no peak splitting and also there is no change in the spectral profile of the hypersensitive transition. The shift of the peak wavelength of the hypersensitive transition towards longer wavelength indicates increase in the covalent nature of Nd-O bond. In the present work, the 4 I 9/ 4 D 3/ + 4 D 5/ splits in two peaks clearly and also there is a change in the spectral profile of the transition from one glass matrix to another glass matrix. It indicates structural changes for different environments. Radiative Properties In the present work, certain radiative properties of Nd 3+ doped different chlorophosphate glasses are estimated using Judd-Ofelt intensity parameters. These radiative properties are radiative transition probabililities (A rad ), radiative lifetimes (τ R ), branching ratios (β R ) and integrated absorption cross-sections (Σ) of different transitions are calculated. The radiative lifetimes (τ R ) for the excited states 4 G 9/, 4 G 7/, 4 G 5/,, H 11/, 4 F 9/, 4 F 5/ and 4 F 9/ are presented in Table from the table, it is observed that radiative lifetimes of all the excited states are minimum for magnesium glass matrix and maximum for sodium calcium glass matrix. The branching ratios (β R ) are more for 4 G 5/ 4 I 9/ transition. Among various glass matrices, magnesium glass matrix showing higher branching ratio values. It is also observed that, the integrated absorption cross-sections (Σ) are higher for 4 G 7/ 4 I 11/ transition. EXCITATION AND EMISSION SPECTRA The emission spectra of Nd 3+ doped different chlorophosphate glass matrix recorded at room temperature in the wavelength region nm under excitation wavelength nm are shown in Figure 3. In the emission spectra, three peaks, 4 I 9/ and 4 I 11/ and 4 I 13/ are observed nearly at 909, 1071 and 1339 nm respectively. From the emission spectra, radiative transitions probabilities (A rad ), branching ratios (β exp ), effective linewidths ( eff ) and emission cross-sections ( p ) of the above three transitions are presented in Table 3. The emission band 5 F 3/ 4 I 11/ at 1071nm has been considered as potential lasing transition due to the large stimulated emission cross-section. From the table it is observed that, among the four chlorophosphate glass matrices, potassium glass has maximum peak emission cross-section. Among three chlorophosphate glass matrices, sodium potassium glass has higher peak emission cross-section (σ p ) values for this transition. Hence this glass matrix may be useful for lasing material. CONCLUSIONS Spectroscopic properties of Nd 3+ doped different chlorophsophate glass have been investigated using optical and emission spectra. The amorphous nature of studied glass matrices is confirmed through XRD profiles. Among four chloro phosphate glass matrices potassium glass matrix showing higher spectral intensities, but three mixed chlorophosphate glass matrix sodium potassium glass showing higher spectral intensity values. The Judd -Ofelt intensity parameters Ω and ΣΩ λ are more sodium, potassium and sodium potassium chlorophosphate glass matrices when compared with other glass matrices. From the radiative properties, it is concluded that radiative lifetimes of all the excited states are minimum for editor@tjprc.org

4 Relative absorbance(a.u) Intensity (counts) 4 D 3/ + 4 D 5/ K 13/ + 4 G 7/ 4 G 5/ + G 7/ 4 F 5/ + H 9/ 6 K. Venkata Rao & Y. C. Ratnakaram magnesium glass matrix and maximum for sodium calcium glass matrix. From the emission spectra, the four chlorophosphate glass matrices, potassium glass has maximum peak emission cross -section. Among three chlorophosphate glass matrices, sodium potassium glass has higher peak emission cross-section (σ p ) values for this transition. Hence this glass matrix may be useful for lasing material. ACKNOWLEDGEMENTS The author K. Venkata Rao expresses his thanks to the University Grants Commission (UGC) for prov iding the financial assistance in the form of minor research project F.No. 4161/1 (MRP/UGC-SERO). REFERENCES 1. J. Li, Y.Z. Mei, C. Gao, F. Ren, A.X. Lu, J.Non-Cryst. Solids 357 (011) Petr Mošner, Kateřina Vosejpková, Ladislav Koudelka, Lionel Montagne, Bertrand Revel, J. Non- Cryst. Solids 357 (011) B.R. Judd, Phys. Rev. 17 (196) G.S. Ofelt, J. Chem. Phys. 37 (196) 511. APPENDICES Na-K Ca K Na (degree) Fig 1. Figure F 7/ + 4 S 3/ K 15/, G 9/, D 3/ 4 G 9/ G 11/ P 1/ H 11/ 4 F 9/ Wavelength(n.m) Fig 1. Optical absorption spectra of Nd 3+ doped alkali and alkalin earth potasium posphate glass Figure : Optical Absorp Spectra of Nd + Doped Alka Li and Alkalin Earth Potassium Phosphate Glass Impact Factor (JCC): Index Copernicus Value (ICV): 3.0

5 Relative Intensity (a.u) 4 I 9/ A Photoluminescence Study of Nd 3+ Doped Different Chloro-Phosphate Glasses for Solid State Laser Applications I 11/ Na-Ca 4 I 13/ Na- Na-K 0.00 Ca K Na Wavelength(nm) Fig 3. Luminesence spectra of Nd 3+ doped different chloroposphate glass Figure 3: Lumlnese Spectra of Nd + Dopped Different Chloro Phosphate Glass Table 1: Judd-Ofelt Intensity Parameters ( X10 0 ) ( =, 4, 6) (Cm )) of Nd 3+ Doped Different Chlorophosphate Glasses S.No Parameter Na K Ca Na-K Na- Na-Ca Ω Ω 4 Ω 6 χ= Ω 4/ Ω Table : Radiative Lifetimes ( R ) ( S) of Certain Excited States of Nd 3+ Ions Doped in Different Chlorophosphate Glasses S. No Nd Excited Level 4 G 9/ 4 G 7/ 4 G 5/ H 11/ 4 G 9/ 4 F 5/ Na K Ca Na-K Na- Na-Ca Table 3: Certain Fluorescence Properties of Nd 3+ Ions Doped in Different Chlorophos phate Glasses S. N o Glass Na K Ca Na-K Na- Na-Ca λ P (nm) I 9/ A rad (s -1 ) ν (cm -1 ) σ P (10-1 cm ) λ P (nm) 4 I 11/ A rad (s -1 ) ν (cm -1 ) 309 σ P (10-19 cm ) λ P (nm) F11 / 4 I 13/ A rad (s -1 ) ν (cm -1 ) σ P (10-1 cm ) editor@tjprc.org

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