Fluorescence Features of Dy³⁺ Doped PbO-Bi₂O₃ Borophosphate Glasses

 

Y.N.Ch. Ravi Babu¹,* S.V.G.V.A. Prasad², M. Kiran Kumar³, A. Suresh Kumar⁴

¹The Hindu College, Machilipatnam-521001, India

²Ideal College, Kakinada-533006, India

³USIC, Sri Venkateswara University, Tirupati -517 502, India

⁴Sri Padmavathi Mahila University, Tirupati -517 502, India

*Corresponding Author E-mail: ynchravibabu@gmail.com

The heavy metal oxide lead bismuth magnesium borophosphate glass systems (LBMBPD)dysprosium ions doped with the molar compositions of (50-x) PbO - x Bi₂O₃-25MgHPO₄-24B₂O₃- 1Dy₂O₃ (where x = 10, 20, 30, and 40 mol %) were prepared using conventional melt quenching technique. The spectral data from the optical absorption photoluminescence were utilized to evaluate various spectroscopic parameters. The Judd-Ofelt parameterization employed reflects the covalency and vibration frequencies of the ligands with dysprosium ions. The radiative parameters such as radiative transition probabilities (A), the total radiative transitional probabilities (A_T), radiative life times (τ_R), branching ratios (β) and absorption cross sections (Ʃ) were computed for certain lasing levels. The emission cross sections (σ_e) for the significant lasing transitions ⁴F_9/2→ ⁶H_13/2 and ⁴F_9/2 → ⁶H_15/2 evaluated from the photoluminescence spectra were reported. The radiative properties thus obtained in our investigations reflect their potentialities as good lasing candidates.

 

KEYWORDS: Judd-Ofelt parameters, hypersensitive transition, Oscillator strengths, Lifetimes, Absorption cross

 

 

1. INTRODUCTION:

The rare earth glass systems are attractive candidates because of their potential applications in solid-state lasers, optical amplifiers and three dimensional displays [1- 4]. Glasses doped with rare-earth ions (RE) are proving to be luminescence materials as they have high emission efficiencies. The attractive characteristic of lanthanides is that they, even though in electrically neutral form, can bind to additional neutral or ionic ligands whereby they can achieve coordination numbers even up to 12 [5]. The potentialities of glasses doped with Dy³⁺ depend on the relative intensities of two prominent emission bands, one yellow band at 576 nm corresponding to ⁴F_9/2→ ⁶H_13/2 and the other blue band at 486 nm corresponding to the ⁴F_9/2→ ⁶H_15/2 transitions. Room temperature peak stimulated emission cross-section (σ_e = 5.57  at 573nm) for ⁴F_9/2→ ⁶H_13/2 transition suggests that Dy-doped lead-borate glass is a promising solid state material for yellow laser applications [6].

 

The yellow to blue intensity ratios (Y/B) of Dy³⁺ luminescence in different hosts indicate the covalency between Dy and oxygen atoms [7]. Also the intense yellow and bright blue emissions measured due to the transitions ⁴F_9/2→ ⁶H_13/2 and ⁴F_9/2 → ⁶H_15/2 from Dy³⁺ doped optical materials could be utilized in the development of solid-state lasers in the visible regions and up-converted lasing systems [8]. Bi₂O₃ in glass systems acts as both network-forming and as well as network modifying ions. For higher valent oxides, such as Bi₂O₃ when used as a modifier, the cation produces important structural effects due to its highest valency. Therefore, the physical properties of such glasses exhibit discontinuous changes when the structural role of the cation switches over in this way [9]. For higher Bi₂O₃ concentration, the presence of bismuth ions affects adversely efficiency of the Dy³⁺ emission [10]. The  glasses containing Bi₂O₃ have drawn attention because of their wide applications in the field of glass-ceramics, thermal and mechanical sensors, reflecting windows, radiation shielding and because they may be used as layers for optical and opto-electronic devices, etc. [11]. The dual role of PbO as a modifier and a glass former [12] draws much attention for it as a favorable candidate for glass fabrication. The quantum efficiency of luminescence from the excited states of RE³⁺ ions is enhanced by the reduction of phonon energy in phosphate glasses [13].

 

The authors in the present work carried out the significant features of PbO in combination with Bi2O3 along with borates and phosphates together to fabricate novel glasses of lead bismuth borophosphate to have good matrix environment for Dy³⁺ ions to yield good potential optical candidates (LBMBPD1, LBMBPD2, LBMBPD3, and LBMBPD4).

 

2. EXPERIMENTAL STUDIES:

2. Experimental studies:

Dy³⁺ doped lead-bismuthate magnesium borophosphate (LBMBPD) glasses that are developed for the present work along with a reference glasses(50-x) PbO - x Bi₂O₃-25MgHPO₄-24B₂O₃- 1Dy₂O₃ (where x = 10, 20, 30, and 40%) were fabricated using conventional melt quenching technique. These glasses are labeled as LBMBPD1, LBMBPD2, LBMBPD3 and LBMBPD4. The starting materials used in the present work were reagent grade of H₃BO₃, PbO, Bi₂O₃, MgHPO₄, 3H₂O and Dy₂O₃. All the chemicals were weighed mixed thoroughly and powdered finely. Each batch of 10 g was taken in a porcelain crucible and melted in an electric furnace for an hour at about 1050⁰C.These melts were quenched in between two brass plates to obtain transparent optical glass discs. These glasses were allowed to anneal at 300⁰C for an hour, to remove thermal strains in the glasses. Due to the lead and bismuth content in the composition of host glass, it appeared in transparent yellow color.

 

The glass samples thus prepared were polished with fine powder of cerium oxide. These developed glass systems were subjected to X-ray diffraction studies for their amorphous nature. The refractive index ’n’ of the samples was determined using conventional methods [14]. Optical absorption spectra were recorded at room temperature on JASCO UV–vis–NIR V–670 spectrometer with the undoped glasses as references. The luminescence spectra of the glass samples were recorded using Perkin Elmer Luminescence Spectrophotometer model LS50B in the spectral range 400–750 nm at the excitation wavelength of 453 nm, which is the strongest absorption band observed in the absorption spectra of the present glass samples.

 

3. RESULTS AND DISCUSSION:

3.1. Physical properties:

The density (d) of the glass systems is measured with the help of Archimedes’s principle and the refractive index (n) values are estimated by conventional methods [14]. The other related physical parameters, such as average molecular weight (M), molar volume (V), molar refractivity (R_M),  electronic polarizability (α_e), Dy³⁺ ion concentration (N), inter ionic distance (r_i), polaron radius (r_P), and field strength (F) of the glasses have been computed by using the relevant expressions available in literature [15-17]. The values of physical properties of these glasses are furnished in Table 1. From Table.1 it is observed that the molar refractivity, electronic polarizability, interionic distance and polaron radius were found to be increased with the increment in Bi₂O₃ (with the decrement in PbO) content and it is observed that the values are higher in LBMBPD4 glass. This is due to the increment in the refractive index. The field strength decreases with Bi₂O₃ content and it is found to be minimum in LBMBPD4 glass. The field strength mainly depends on the anionic and cationic ratio in the glass matrix.

 

3.2. Absorption spectra:

Fig.1 represents the vis–NIR absorption spectrum of Dy³⁺ ion with strong absorption bands in the NIR region. The bands are assigned from the ground state ⁶H_15/2. The absorption spectra consist six bands corresponding to ⁶H_15/2→ ⁶F_3/2, ⁶F_5/2, ⁶F_7/2, ⁶F_9/2, ⁶F_11/2 and ⁶H_11/2 transitions. The absorption transitions due to thermalization from the first excited ⁶H_13/2 level are ruled out because of the large energy gap (3300 cm^-1) between ⁶H_15/2 and ⁶H_13/2 levels. The position and intensity of certain transitions of rare-earth ions are found to be very sensitive to the environment around the ion. Such transitions are termed as hypersensitive transitions [18].

 

 

Table 1. Physical properties of Dy³⁺ ions doped in LBMBPD1-4 Glasses.

Physical property	LBMBPD1	LBMBPD2	LBMBPD3	LBMBPD4
Averaege molecular weight	198	222	247	271
Density (gm/cm3)	4.35	4.56	4.72	4.81
Refractive index’ n’	1.972	1.979	1.986	1.992
concentration N (1022 ions/cm3)	1.32	1.24	1.15	1.07
Polaron radius ‘rp’ (A0)	3.65	3.74	3.83	3.92
Inter ionic distance ‘ri’ (A0)	4.23	4.32	4.43	4.54
Field strength  F (1016 cm-2)	0.23	0.22	0.21	0.20
Molar refractivity RM(cm-3)	22.3	24.0	25.9	28.0
Electronic polarizability α (10-24 cm-3)	0.88	0.95	1.03	1.11
Molar volume Vm	45.5	48.7	52.3	56.4
Optical dielectric constant ϵ Bonding  parameter  δ	2.89 -1.363	2.92 -1.199	2.94 -1.321	2.97 -1.201

 

Figure 1. VIS-NIR absorption spectrum of Dy3+ ions doped LBMBP glasses. (A)LBMBPD1 (B) LBMBPD2 (C) LBMBPD3 and (D) LBMBPD4 glasses

 

They will follow the selection rules ∆J ≤ 2, ∆L ≤ 2, ∆S = 0. For Dy³⁺ (4f⁹) ion, ⁶H_15/2→⁶F_11/2 is the hypersensitive transition. The intensity of hypersensitive ⁶H_15/2→⁶F_11/2 transition increases as the bismuth content increases from LBMBPD1 to LBMBPD4 glasses as shown in Table.2

 

3.3. Oscillator strengths and Judd–Ofelt analysis:

The intensities of an absorption bands are expressed in terms of their oscillator strengths. J–O theory [19, 20] has been applied to evaluate the intensity parameters Ω_k (k = 2, 4, 6) from the measured spectral intensities of absorption bands. The experimentally measured oscillator strengths (f_exp) of absorption bands have been obtained from the expression

 

 

Where ε is the molar extinction coefficient which can be calculated using the Beer–Lambert law at energy υ cm^-1  was evaluated by measuring the area under the curve shown in Fig.1.

 

Oscillator strengths have been measured for all these absorption bands and are presented in Table 2. In order to estimate the calculated oscillator strengths (f_cal) and intensity parameters (Ω_k), the f_exp values are fitted by the least squares method using the equation [19, 20] and are presented in Table 3. The position and spectral intensities of certain transitions of rare-earth ions are found to be very sensitive to the environment of the rare-earth ion. They will follow the selection rules ∆J ≤ 2, ∆L ≤ 2, ∆S = 0 and such transitions are called as hypersensitive transitions. For Dy³⁺ ion, ⁶H_15/2→⁶F_11/2 (⁶H_9/2) is the hypersensitive transition. The intensity parameter Ω₂, which indicates covalency, decreases with the decrease of intensity of hypersensitive transition. Hyper sensitivity related to covalency affects polarizability of the ligands around RE ions and higher ligand polarizability results in a larger overlap between RE ions and ligand orbital [21].

 

The higher magnitude of Ω₂ in the present work indicates the increase of covalent bonding and suggests that the Dy³⁺ ion posses higher site asymmetry in LBMBPD glass host.

 

The Ω₆ is related to the rigidity of the host and also vibronic dependent [27]. The higher Ω₂ and Ω₆ [28] values may be indicative of higher polarizability of the lanthanide environment and strong covalent interactions. The stimulated emission in any host glass matrix can be characterized with help of spectroscopic quality factor Ω_2/Ω₆. The values of Ω_2, Ω₄ and Ω₆ for the present glass systems are compared with the other hosts in the literature presented in the Table.3. The values of Ω₂ are observed to be increased with the increment of bismuth content in our present glass systems as in Table.3. It is also confirmed by the values of bonding parameters of the present glass samples presented in the Table 1. The values of the bonding parameters for the present glass samples are –ve indicating the ionic environment, but the trend of –ve values of bonding parameters shows decrement from LBMBPD1 to LBMBPD4. Hence covalency increases from LBMBPD1 to LBMBPD4 due to increment of bismuth content.

 

3. 4. Radiative properties:

The J-O intensity parameters have been used to compute the radiative properties of emission characteristics of the Dy³⁺doped lead- bismuthate magnesium borophosphate (LBMBPD) glasses. Using the relevant expression available in literature [29], the radiative transition probabilities, lifetimes and branching ratios are estimated for the transitions of the Dy³⁺ and are presented in Table 4. From the values of radiative transition probabilities of Table 4, it is noticed that ⁴F_9/2→ ⁶H_13/2 transition has highest radiative transition rate compared to other transitions. Hence this transition is very useful for laser emission. The predicted branching ratios are found to be high for these transitions having maximum A_R values. The levels having the relatively large values of A, β_R and energy gap to the next lower level may exhibit laser action. The branching ratios of the emission transitions ⁴F_9/2 →⁶H_15/2 and ⁴F_9/2 →⁶H_13/2 exhibit 63%   and 37% indicate its lasing potentiality. Electric dipole line strength (S_ed), branching ratios (β), integrated absorption cross sections (Σ) and radiative life times (τ_R) for the exited states of Dy³⁺ion have been calculated and presented in Table 4. The radiative transition probabilities (A) and total emission probability (A_T) can be evaluated from the relations I n the literature [29]. Total emission probabilities are increased with the bismuth content. These values are presented in Table 4.

 

 

Table 2. Experimental and calculated spectral intensities (f×10^-6) of observed absorption bands of Dy³⁺ ion  doped in  LBMBPD1-4 Glasses.

Transition 6H15/2→	LBMBPD1		LBMBPD2		LBMBPD3		LBMBPD4
	fexp	fcal	fexp	fcal	fexp	fcal	fexp	fcal
6F3/2	0.28	0.28	0.29	0.23	0.24	0.29	0.43	0.42
6F5/2	2.41	1.47	2.62	1.23	2.36	1.58	3.73	2.24
6f7/2	2.56	3.22	3.0	2.99	4.53	3.67	3.97	4.95
6F9/2	4.14	3.99	4.13	4.4	4.5	5.02	6.41	6.21
6F11/2	11.7	11.7	12.2	12.7	13.1	13.7	18.2	18.2
6H11/2	2.1	2.05	1.38	1.87	1.49	2.24	3.20	3.14
Rms. dev.	0.09		0.12		0.10		0.09

 

Table 3. Comparison of Judd-Ofelt  intensity parameters (Ω_λ ×10^-20) (λ=2, 4, 6) (cm²) of Dy³⁺ ions in different glass environments.

Glass	Ω2	Ω4	Ω6	Ω4/Ω6	References
LBMBPD1	9.21	2.5	2.58	0.97	Present work
LBMBPD2	9.3	3.59	2.14	1.68	Present work
LBMBPD3	9.53	3.51	2.61	1.35	Present work
LBMBPD4	13.9	3.90	3.87	1.01	Present work
Dy: LiLTB	8.75	2.62	2.07	1.27	[22]
Dy: NaLTB	9.25	2.87	2.29	1.25	[22]
Dy: KLTB	9.86	3.39	2.41	1.41	[22]
PKMFDy	7.04	1.73	1.57	1.10	[23]
NaZnBS	16.82	9.45	6.50	1.45	[24]
Oxyfluoroborate	2.68	2.56	0.89	2.87	[25]
PbO-PbF2	2.13	2.10	1.00	2.1	[26]

 

Table 4. Estimated values of spontaneous emission  probabilities ‘A’ (s^-1), branching  ratios (β), absorption cross-sections ‘∑’ (cm²) total radiative probabilities‘A_T’ (s^-1), and radiative lifetimes ‘τ_R’(ms) of Dy³⁺ions doped in LBMBPD1-4 Glasses.

Transition		LBMBPD1			LBMBPD2			LBMBPD3			LBMBPD4
SLJ   →   S'L'J'		A	β	∑	A	β	∑	A	β	∑	A	β	∑
4F9/2	6F5/2	23.49	0.01	0.09	24.28	0.01	0.09	25.18	0.01	0.09	36.9	0.01	0.14
	6H7/2	44.69	0.02	0.09	51.1	0.02	0.10	54.46	0.02	0.11	70.9	0.01	0.15
	6F9/2	21.68	0.01	0.04	28.05	0.01	0.05	28.25	0.01	0.06	34.7	0.01	0.07
	6F11/2	60.78	0.02	0.10	65.38	0.02	0.11	68.41	0.02	0.11	95.9	0.02	0.15
	6H9/2	47.25	0.02	0.08	49.84	0.02	0.08	52.99	0.02	0.08	74.5	0.02	0.12
	6H11/2	204.6	0.07	0.26	210.0	0.07	0.26	219.9	0.07	0.28	321.8	0.07	0.40
	6H13/2	2007	0.69	1.91	2027	0.70	1.93	2166	0.69	2.06	3155	0.69	3.01
	6H15/2	462.7	0.16	0.31	421.9	0.15	0.28	501.4	0.16	0.33	723.8	0.16	0.48
	AT	2872		AT	2877		AT	3117		AT	4514
	τR	0.348		τR	0.347		τR	0.321		τR	0.222
4F7/2	6F1/2	171.9	0.01	0.35	175.7	0.01	0.36	182.2	0.01	0.37	270.3	0.01	0.55
	6F3/2	76.96	0.01	0.14	111.9	0.01	0.21	110.6	0.01	0.21	124.5	0.01	0.23
	6F5/2	179.0	0.01	0.29	218.1	0.01	0.36	220.6	0.01	0.36	285.2	0.01	0.47
	6F7/2	366	0.03	0.49	435.7	0.03	0.59	441.9	0.03	0.59	582.3	0.03	0.78
	6H5/2	138.4	0.01	0.17	144.4	0.01	0.17	160.2	0.01	0.19	218.3	0.01	0.26
	6H7/2	332.4	0.02	0.35	319.6	0.02	0.34	361.9	0.02	0.38	521.3	0.02	0.55
	6F9/2	1925	0.13	2.04	2064	0.13	2.19	2125	0.13	2.25	3038	0.13	3.22
	6F11/2	4173	0.29	3.80	4358	0.28	3.97	4503	0.27	4.10	6572	0.29	5.98
	6H9/2	308.9	0.02	0.28	327.4	0.02	0.29	354.4	0.02	0.32	487.5	0.02	0.44
	6H11/2	2624	0.19	1.96	2875	0.18	2.14	2953	0.18	2.20	4147	0.18	3.09
	6H13/2	882.5	0.06	0.53	877.3	0.05	0.52	1003	0.06	0.59	1387	0.06	0.83
	6H15/2	2966	0.21	1.33	3807	0.24	1.71	3933	0.24	1.76	4750	0.21	2.13
	AT	14147		AT	15716		AT	16350		AT	22385
	τR	0.0707		τR	0.0636		τR	0.0612		τR	0.0447

 

 

4.5. Luminescence spectra:

The emission spectra of Dy³⁺ doped lead-bismuthate magnesium borophosphate (LBMBPD) glasses were recorded in the visible region (400–700 nm) by exciting at 453 nm are shown in Fig. 2. It consists of two intense emission peaks are observed at 485 (blue) and 577 nm (yellow). They correspond to the emission from the ⁴F_9/2 →⁶H_15/2 and ⁴F_9/2 →⁶H_13/2 transitions respectively. For ⁴F_9/2→⁶H_15/2 and ⁶H_13/2 transitions the predicted branching ratios are found to be 15% and 65%, whereas the measured branching ratios are 63% and 37% respectively. The variation between the predicted and measured branching ratios may be due to the presence of heavy metal oxides bismuth and lead content that decreases the phonon energy [30] in the present glasses. The host materials with low phonon energies have been used for obtaining high efficiency lasers and fiber amplifiers [31].  ⁴F_9/2 →⁶H_15/2 and ⁴F_9/2 →⁶H_13/2 transitions are due to magnetic dipole (MD) and electric dipole (ED) transitions. In the present work, ⁴F_9/2 →⁶H_13/2 (ED) transition of Dy³⁺ ions is less intense than ⁴F_9/2 →⁶H_15/2 (MD) specifying the symmetric nature of the glass host. But intensity of ⁴F_9/2 →⁶H_13/2 increases with the increment of bismuth content from LBMBPD1 to LBMBPD4 indicating that asymmetric nature increases which is also confirmed by the Ω₂ values and bonding parameter δ values. The ⁴F_9/2 → ⁶H_13/2 transition belongs the hypersensitive transition with ∆J=2, which is strongly influenced by the outside environment of Dy³⁺ [32].

 

Figure 2. Emission spectrum of  Dy³⁺  ions doped (A) LBMBPD1 (B) LBMBPD2(C) LBMBPD3 and (D) LBMBPD4 glasses

 

Similar observations have also been reported for Dy³⁺-doped RTFP glasses [33]. The ratio of intensities of yellow and blue emission transitions (Y/B) strongly depends on concentration and glass composition [6]. In the present glass systems the Y/B ratios are found to be 0.574, 0.622, 0.788, and 0.673 for LBMBPD1 to LBMBPD4 glasses. The higher values of Y/B indicate the higher degree of covalency between Dy and Oxygen atoms [6].

 

The effective band widths and stimulated emission cross-sections are evaluated [34] for these transitions using the following expressions and are presented in Table.5. The comparative studies of effective band widths and stimulated emission cross-sections for various Dy³⁺ doped glass systems were furnished in the Table 5.

 

 

Where I (λ) is the emission intensity at the wave length peak.

Stimulated emission cross-section σ_e =

(3)

 

From the fluorescence spectra, it is observed that the intensities of the fluorescent transitions ⁴F_9/2 →⁶H_15/2 and ⁴F_9/2 →⁶H_13/2 increase from LBMBPD1 to LBMBPD4. It is also found that the emission peak positions do not vary much with host to host (Fig.2). It is interesting to note that the following lasing transitions show incremental tendency for the values of stimulated emission cross-section from host to host as detailed below:

 

Transition ⁴F_9/2 → ⁶H_13/2: LBMBPD3< LBMBPD1 < LBMBPD2 < LBMBPD4

Transitions ⁴F_9/2 →⁶H_15/2: LBMBPD3< LBMBPD2 < LBMBPD1 < LBMBPD4

 

Table 5. Certain radiative and fluorescence properties Stimulated emission cross-sections σ_e (10^-22 cm²⁾, effective band width Δλ (nm), peak wave  length λ_p(nm), predicted branching ratios  β and Spontaneous emission probabilities A_rad of  Dy³⁺  ions doped in LBMBPD1-4 Glasses.

4F9/2 → 6H15/2					4F9/2 → 6H13/2
Glass	λp	Δλ	σE	β	λp	Δλ	σE	β
LBMBPD1 [Present work]	485.5	17.4	5.041	0.16	577.5	16.7	45.61	0.69
LBMBPD2 [Present work]	485.5	18.1	4.387	0.15	577.5	16.1	47.44	0.70
LBMBPD3 [Present work]	485	23.8	3.921	0.16	578	22.5	36.14	0.69
LBMBPD4 [Present work]	485	23.2	5.772	0.16	578	22.5	52.33	0.69
Dy:LiLTB [22]	481	-	-	0.50	572	22	21.86	0.44
B2O3-ZnO-PbO [35]	484	24.0	16.1	-	576	16	37.8	-
Dy3+ doped (SeOcl2+Sncl4)laser liquids  [36]	482.8	12.5	6.5	0.39	576.4	11.1	19.2	0.49

 

 

4. CONCLUSIONS:

The A novel class of heavy metal oxide lead bismuth magnesium borophosphate glass systems (LBMBPD) dysprosium ions doped with the molar compositions of (50-x) PbO - x Bi₂O₃-25MgHPO₄-24B₂O₃- 1Dy₂O₃ (where x = 10, 20, 30, and 40 mol %) were prepared and characterized. The optical properties, viz., absorption and photoluminescence of Dy³⁺ ions were studied and related to the host matrix nature. A strong dependence of the J-O parameter, Ω₂ on the hypersensitive transition has been demonstrated. The J-O parameter Ω₂ value indicates that these doped glasses are more covalent in nature. Strong yellow and blue emissions were observed upon the 453 nm excitation wavelengths. The evaluated laser characteristic parameters for ⁴F_9/2→⁶H_13/2  transition corresponding to 576 nm supports that the present glasses are the good candidates for laser action to produce intense emission. The emission intensity ratios of yellow and blue transitions, Y/B, of Dy³⁺ ions indicate the strong covalent nature and dependence on the local environment in which the RE ions are occupied. Usually, a good material for laser emission should have high radiative transition rates and high branching ratios. Based on optical properties such as strong visible emissions and high branching ratios, it is concluded that Dy³⁺ ions doped LBMBPD4 glass may be used as a luminescent novel optical material for the development of lasers and photonic devices operating in the visible region.

 

5. ACKNOWLEDGEMENTS:

One of the authors Y. N. Ch. Ravi Babu is thankful to University Grant Commission, New Delhi, for granting him Faculty Development Programme to carry out his Doctoral degree.

 

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Received on 04.07.2014         Modified on 20.07.2014

Accepted on 07.10.2014         © AJRC All right reserved