Crystal structure, synthesis and photoluminescent properties of a reddish-orange light emitting SrGdAlO4: Sm3+ nanophosphor

Accepted Manuscript Crystal structure, synthesis and photoluminescent properties of a reddish-orange light 3+ emitting SrGdAlO4: Sm nanophosphor Anju Hooda, S.P. Khatkar, Avni Khatkar, R.K. Malik, Jyoti Dalal, Sushma Devi, V.B. Taxak PII:

S0254-0584(19)30352-9

DOI:

https://doi.org/10.1016/j.matchemphys.2019.04.054

Reference:

MAC 21574

To appear in:

Materials Chemistry and Physics

Received Date: 15 December 2018 Revised Date:

8 April 2019

Accepted Date: 21 April 2019

Please cite this article as: A. Hooda, S.P. Khatkar, A. Khatkar, R.K. Malik, J. Dalal, S. Devi, V.B. Taxak, Crystal structure, synthesis and photoluminescent properties of a reddish-orange light emitting 3+ SrGdAlO4: Sm nanophosphor, Materials Chemistry and Physics (2019), doi: https://doi.org/10.1016/ j.matchemphys.2019.04.054. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT

Crystal structure, synthesis and photoluminescent properties of a reddish-orange light emitting SrGdAlO4: Sm3+ nanophosphor Anju Hoodaa, S.P. Khatkara, Avni Khatkarb, R.K. Malika, Jyoti Dalala Sushma Devia, V.B.

a

b

RI PT

Taxaka* Department of Chemistry, Maharshi Dayanand University, Rohtak -124001, India

University Institute of Engineering and Technolgy (UIET), Maharshi Dayanand University,

*

SC

Rohtak, India

Corresponding author: Tel: 9466722544

M AN U

E-mail: [email protected] Abstract

A series of reddish orange light emitting SrGdAlO4: Sm3+ nanophosphor was prepared by urea aided solution combustion process. Structural features of the prepared nanophosphor were described by the powder X-ray diffraction (PXRD) together with Rietveld refinement technique.

TE D

The results authenticate the existence of single phased tetragonal lattice with space group of I4/mmm (139). The highly intense peak observed in the photoluminescence emission spectra of the synthesized nanocrystalline phosphors was observed at 600 nm owing to 4G5/2 → 6H7/2 transition upon excitation by 407 nm light. The estimated energy band gap of SrGd0.97Sm0.03AlO4

EP

nanophosphor was found to be 5.45 eV. The critical distance value evaluated for non-radiative energy transfer comes around 17.52 Å. The main reason responsible for the observed

AC C

concentration quenching phenomenon in emission intensity of the prepared nanophosphor beyond 3 mol % doping of Sm3+ was found to be dipole-dipole (d-d) type electric multipolar interaction. The refractive index of the optimized nanophosphor (SrGd0.97Sm0.03AlO4) comes around 1.682. The chromaticity coordinates were found to lie in the reddish-orange region of CIE (Commission Internationale De I’Eclairage) diagram. The vivid description of the photoluminescent and structural aspects validate the potential applications of synthesized nanophosphor as optical nanomaterials in phosphor converted white light emitting diodes (pcWLEDs).

1

ACCEPTED MANUSCRIPT

Keywords: Solution Combustion; Optical Materials; Photoluminescence; Nanomaterials; SrGdAlO4:Sm3+ 1. Introduction

RI PT

Recently, inorganic nanomaterials doped with trivalent lanthanide ion have become cynosure of scientists related to entire field of science and technology due to their excellent physico-chemical features and plausible applications in profuse areas belonging to solid state lighting (SSL), display panels, phosphor converted white light emitting diodes (Pc-WLEDs) and various

SC

electronic devices [1–4]. The efforts for improving luminescent nanomaterial properties are constantly being made by different scientists mainly because of a great demand of these

M AN U

materials possessing exceptional photometric and structural features. Traditionally, the technique of fabrication of WLEDs was associated with the blending of blue InGaN LED chip (λex = 450470 nm) along with the covering of trivalent cerium doped yellow light emitting phosphor material YAG i.e. Y3Al5O12: Ce+3 [5,6]. Nevertheless, this approach bears various limitations regarding high correlated color temperature (CCT), low color rendering index (CRI) by means of inadequate reddish component requisite for SSL. The modern pathway for fabricating WLEDs is

TE D

related to applying coating of UV or near ultraviolet (NUV) LED chips (λex = 450-470 nm) over tricolor RGB (red, green and blue) phosphors [7]. WLEDs synthesized via these approaches have effectively replaced conventionally used fluorescent and incandescent lamps attributable to their remarkable features like eco-friendly nature, long-term performance, better fidelity, quick

EP

response, low power necessity, superior luminescence efficiency etc. [8,9]. A proper host lattice [10–12] is usually required for doping various types of trivalent rare-earth

AC C

ions to synthesize a nanophosphor that emits light after excitation by a near-ultraviolet light source [13–15]. Generally, inorganic compounds having lanthanide ions (Ln3+) possessing electronic configuration of [Xe] 4f0 or [Xe] 4f7 or [Xe] 4f14 type are considered as good host material for the synthesis of nanophosphors because of negligible probability of occurrence of quenching effect via cross relaxation by these types of Ln3+ ions. Thus, in this context, SrGdAlO4 matrix possessing Gd3+ ions ([Xe] 4f7) is preferred choice to act as an excellent luminescence host lattice. Moreover, the presence of additional desirable properties in SrGdAlO4 lattice such as low toxicity, high chemical and thermal stability, environmental friendliness, ability to adjust large sized Ln3+ ions etc. make its extensive use possible as a commendable host 2

ACCEPTED MANUSCRIPT

matrix. At the same time, aluminate nanophosphors [16–20] attracts substantial attention of material’s scientists by virtue of their higher efficiency, longer lifetime and brightness of betterquality etc in contrast with other type of host lattices such as oxides [21–25], molybdates [26], sulphides [27], tungstates [28,29], titanates [30] and so on. Among various rare-earth ions, Sm3+

RI PT

ion is considered as a versatile dopant ion in different host matrices due to its characteristic reddish-orange emission in numerous solid state lighting applications. Likewise, trivalent samarium (Sm3+) as a dopant ion in a stable luminescent host matrix like aluminate type lattice [31–34] exhibits strong orange or reddish-orange emission afterwards doping [35,36]. SrGdAlO4

SC

host matrix is an appropriate lattice for doping of trivalent lanthanide ion owing to its remarkable features of high stability and better photoluminescent characteristics. This research work is novel

M AN U

as until now, there is no study reported on photoluminescence properties of trivalent samarium doped SrGdAlO4 matrix. This is the first report on crystal structure analysis and photoluminescent features of combustion synthesized SrGdAlO4: Sm3+ nanophosphor. In view of this, a detailed investigation of structural and photoluminescent characteristics of SrGdAlO4: Sm3+ nanophosphor synthesized via solution combustion synthesis process is reported. Rietveld refinement of host lattice and optimum composition of SrGdAlO4: Sm3+ nanophosphor is carried

TE D

out to determine crystal structure by utilizing PXRD data. Band gap analysis from DRS also facilitates the determination of refractive index of optimized nanophosphor. The morphological features are characterized by SEM (scanning electron microscope) and TEM (transmission electron microscope) techniques. The excellent orange-red color emission from the synthesized

EP

nanophosphors is revealed by the photometric characterizations disclosing the outstanding color chromaticity coordinates which proves their usefulness in solid state lighting and display

AC C

systems. 2. Experimental

2.1. Materials and Methods Solution combustion synthesis (SCS) technique, a remarkably good wet chemical method was adopted for the synthesis of SrGdAlO4: Sm3+ nanophosphor. To accomplish this process, initially metal nitrates of high grade (Sr(NO3)2), Gd(NO3)3.6H2O, Al(NO3)3.9H2O, Sm(NO3)3.6H2O) as oxidizer and urea (NH2CONH2) as fuel procured from Sigma Aldrich were mixed in a little quantity of deionized water taken in a beaker. The estimation of stoichiometric proportion of 3

ACCEPTED MANUSCRIPT

oxidizer and fuel used, was carried out via propellant chemistry [37]. An exothermic redox reaction then took place among the homogeneous mixture (oxidizer + fuel taken in unit ratio) causing oxidation of fuel and reduction of metal nitrates in beaker placed for few minutes in Muffle furnace having temperature of 500˚C. The whole mixture ignites evolving heat and light

RI PT

resulting into high temperature in furnace leading to crystallization and production of fluffy product.

The chemical reaction yielding SrGd0.97Sm0.03AlO4 nanophosphor can be represented by the

SC

following chemical equation

Sr(NO3)2 + 0.97 Gd(NO3)3 . 6H2O + 0.03 Sm(NO3)3 . 6H2O + Al(NO3)3 . 9H2O

M AN U

+ 6.67 NH2CONH2 → SrGd0.97Sm0.03AlO4 + 6.67 CO2 (g) + 28.33 H2O (g) + 10.67 N2 (g) The resulted product after cooling to room temperature was finally pulverized to fine powder form. The obtained powder was then transferred in an alumina crucible for sintering at 1300˚C for 3h. Finally, the required nanophosphor was obtained with high crystallinity upon cooling to room temperature.

TE D

2.2. Characterizations

PXRD data acquisition of finely powdered undoped and trivalent samarium doped SrGdAlO4 samples in range of

2θ = 10˚ - 80˚ was done using Rigaku Ultima IV Powder X-Ray

diffractometer exhibiting Cu-Kα radiation of wavelength 1.540562 Å as X-ray generating source

EP

at an operating current and voltage of 40 mA and 40 kV respectively with scanning rate of 2 degree per minute. The Rietveld refinement technique was implemented over recorded PXRD patterns (scan rate of 1˚ min-1) of host matrix and SrGd0.97Sm0.03AlO4 nanophosphor by

AC C

employing General Structure Analysis System (GSAS) package. Tecnai G2 FEI TEM machine was used for TEM analysis, whereas SEM analysis was carried out via Zeiss EVO 18 Special. Elemental analysis was carried out using energy dispersive X-ray (EDS) machine. The photoluminescence (PL) data procurement was carried out via Hitachi F-7000 Fluorescence Spectrophotometer equipped with xenon lamp. Recording of excitation and emission spectra were performed with scanning speed of 1200 nm per minute keeping photo multiplier tube voltage (PMT) at 400 V and utilizing slit widths of 2.5 nm. The analysis of luminescence decay curves was executed via applying 5 nm slit widths with PMT of 700 V and chopping speed of 40 4

ACCEPTED MANUSCRIPT

Hz. The color coordinates (x,y) were interpreted at 407 excitation wavelength by virtue of CIE 1931 Chromaticity diagram utilizing MATLAB programme. 3.1. Structural Properties

RI PT

SrGd(1-x)SmxAlO4 (x = 0.5 - 15 mol %) samples sintered at 1300˚C for 3h were characterized by PXRD technique. The resulted diffraction patterns for undoped and doped system are displayed in Fig. 1 which show exact match with standard host lattice SrGdAlO4 belonging to JCPDS card no. 24-1185. The outcomes of PXRD technique confirm tetragonal phase along with the space

SC

group I4/mmm (139) of the prepared series of nanophosphor. It seems that dopant ions (Sm3+) are replacing the Gd3+ ions; inspite of other cations present in SrGdAlO4 host matrix owing to their

M AN U

similar size and identical charge. Although, Al3+ also possesses same charge, yet it is not substituted by dopant ions on account of their different size. This particular replacement phenomenon can be better understood by determining radius percentage difference among various ions. For this, effective ionic radii of ions are used in the following equation ∆r =



× 100

TE D

Where, CN represents the coordination number,

and

(1) are representing the

effective ionic radii of host cations and doped cations respectively. The effective ionic radius of Sm3+ ion ( of Al3+ ion (

= 0.96Å, CN = 9) lies close to Gd3+ ion (

= 0.93Å, CN = 9) and differ from that

= 0.53Å, CN = 6). Since, ∆r acceptable value is less than 30%. It is observed that

EP

∆r value between Gd3+ (host cation) and Sm3+ ions is 3.2 % which is lower than 30% which confirms replacement of only Gd3+ ions via Sm3+ ions among other cations present in host

AC C

matrix. Substitution of Al3+ ions by Sm3+ ions is also ruled out as a result of radius percentage difference (∆r) value calculated between Al3+ and Sm3+ ions which comes around 81.1 %. Scherrer’s formula utilizing the full width at half maxima of the prominent peak confirms the nanocrystalline nature of the prepared nanophosphors as the crystallite size was found to lie in nano-range [38].

Rietveld refinement shown in Fig. 2 is carried out over SrGd0.97Sm0.03AlO4 nanophosphor sintered at 1300˚C for evaluation of lattice parameters. The goodness of fit was determined in terms of χ2 = 2.266, Rp = 4.68 and wRp = 6.01. The comparison of data related to crystal 5

ACCEPTED MANUSCRIPT

structure is also done among SrGd0.97Sm0.03AlO4 lattice and standard host matrix (listed in Table 1). Besides this, several refined parameters in Rietveld refinement for SrGd0.97Sm0.03AlO4 nanophosphor are also indexed in Table 2. The outcomes of this technique revealed the slight increment in volume of unit cell for SrGd0.97Sm0.03AlO4 matrix from standard host lattice

RI PT

because of substitution of Gd3+ ion by Sm3+ ion which may be due to nominally greater ionic radius of Sm3+ ion than Gd3+ ion. Both the results (minor expansion in unit cell volume and decrement in Formula weight of doped lattice than undoped) clearly revealed the negligible decrease in density of trivalent samarium doped SrGdAlO4 lattice in comparison to undoped host

SC

matrix. Fig. 3 portrays the unit cell of SrGd0.97Sm0.03AlO4 matrix obtained via Diamond software after providing the information regarding structural features acquired by Rietveld analysis. The coordinating environment of different kind of cations present in SrGd0.97Sm0.03AlO4 lattice is

M AN U

also thoroughly assessed in this figure disclosing that Gd3+/ Sm3+/ Sr2+ ions have CN of 9 and Al3+ ion has CN of 6. Numerous interatomic distances are compiled in Table 3. EDS analysis of the optimized nanophosphor (SrGd0.97Sm0.03AlO4) and 15 mol% Sm3+ doped SrGdAlO4 nanophosphor sintered at 1300˚C is displayed in Fig. 4 (a) and Fig. 4 (b) respectively confirming the efficient doping of trivalent samarium ion in the host matrix and the results prove

TE D

that the synthesized nanophosphors are comprised of Sr, Gd, Al, O and Sm elements. Fig. 4 (c) and 4 (d) displays SEM and TEM images of SrGd0.97Sm0.03AlO4 phosphor sintered at 1300˚C. It is clearly observed from Figure 4 (c) that the phosphor sample consists of particles with nearly spherical morphologies. TEM image shown in Figure 4 (d) reveals that the size of particles of

EP

optimized phosphor lies in nano-range from 25-55 nm. The luminescent properties shown by nano-size particles are better comparative to the bulk material as a result of less internal

AC C

scattering and more surface area to volume ratio. 3.2. Photoluminescence Properties Fig. 5 demonstrates PLE (photoluminescence excitation) spectrum of SrGd0.97Sm0.03AlO4 nanocrystalline phosphor sintered at 1300˚C on rooting λem at 600 nm. The PLE studies show that the spectrum can be analyzed in two parts. Among them, one part is a weak broad band situated in range of 200 nm to 265 nm having maxima at 238 nm which usually results due to electron migration via charge transfer state from 2p shell of oxide ions to 4f shell of Sm3+ ions. The less intense band indicates feeble dopant ions interaction with the host matrix. The energy of 6

ACCEPTED MANUSCRIPT

O2- → Sm3+ charge transfer band (ECT in cm-1) is determined with the help of equation given by Jorgenson [16]. ECT = [χ (L) – χ (M)] (3 × 104)

(2)

RI PT

Where, x(L) and x(M) are representing the opto electronegativity of oxide ion (O2-) and dopant ion (Sm3+) respectively. In this work, χ (O2-) = 3.2 and χ (Sm3+) = 1.17, the evaluated charge transfer position utilizing equation 2 should be 60900 cm-1 (~ 164 nm). However, the position of this band measured by PLE spectra of resulted samples lie around 238 nm. The shift in the

SC

position of charge transfer band occurs because of differences among bulk materials and nanophosphors [39,40]. On the other hand, the other part consists of numerous sharp peaks lying in range of 340 to 500 nm which arises mainly because of typical f-f transitions of Sm3+ ions.

M AN U

The peaks are associated to 6H5/2 → 4D7/2 (347 nm), 6H5/2 → 4F9/2 (364 nm), 6H5/2 → 4D5/2 (378 nm), 6H5/2 → 6P7/2 (391 nm), 6H5/2 → 4K11/2 (407 nm), 6H5/2 → 6P5/2 + 4M19/2 (421 nm), 6H5/2 → 4

F5/2 + 4I13/2 (468 nm) and 6H5/2 → 4I11/2 + 4M15/2 (493 nm) transitions [41,42].

Fig. 6 illustrates photoluminescence emission spectra of SrGd(1-x)SmxAlO4 (x = 0.5-15 mol %) nanophosphors recorded at excitation wavelength of 407 nm. Sm3+ ions upon excitation

TE D

undergoes 6H5/2 → 4K11/2 transition and these excited dopant ions finally relaxed to 4G5/2 level by means of several non-radiative transitions. Various energy levels exist between 4K11/2 and 4G5/2 (as depicted in Fig. 7) states with lesser energy differences among them which favor nonradiative transitions causing increase in population of 4G5/2 level and eventually resulted into

EP

numerous emission peaks from this state to different ground state levels. Thus, the major emission peaks of Sm3+ peaks arises as a result of 4G5/2 → 6H5/2, 4G5/2 → 6H7/2 and 4G5/2 → 6H9/2

AC C

transitions lying at 565 nm, 600 nm and 647 nm respectively [43,44]. Among these emission peaks, the most prominent peak is examined at 600 nm arising due to 4G5/2 → 6H7/2 transition (∆J = 1) which is actually a magnetic dipole (MD) transition. The transitions obeying selection rule of ∆J = 0, ±1 are usually MD transitions, nevertheless, transitions obeying ∆J ≤ 6 (expecting 0 and ±1) selection rule are electric dipole (ED) transitions [45]. So, it is clear here that 4G5/2 → 6

H5/2 is MD transition, whereas 4G5/2 → 6H9/2 is associated to ED transition. To explore

information about the local environmental symmetry of trivalent samarium ions, the intensity ratio of 4G5/2 → 6H7/2 (MD) transition to 4G5/2 → 6H9/2 (ED) transition at 600 nm and 647 nm respectively is calculated and represented in Fig 8. All the transitions related to 7

ACCEPTED MANUSCRIPT

photoluminescence spectra are compiled in Table 4. As variation in dopant ion content highly affects the luminescence properties of the synthesized nanophosphor, therefore, our focus is to find out the optimal composition for better photoluminescence performance. The optimum composition can be determined via observing concentration quenching phenomenon which is

RI PT

clearly shown in Fig 9. The figure clearly demonstrates that photoluminescence emission intensities for synthesized nanophosphors starting from 0.5 mol % Sm3+ content firstly increases upto 3.0 mol % dopant concentration, attained maxima at this composition and then starts decreasing with higher dopant level because of concentration quenching. The quite possible

SC

reason for the occurrence of quenching phenomenon may be due to cross-relaxation processes taking place among the adjacent Sm3+ ions owing to decrease in distance among them with the increment in dopant content. If the distance is found to be less than the critical distance, then

M AN U

there is immense possiblility of transfer of energy between neighboring Sm3+ ions and finally attains quenching sites, instead of release of energy via dopant ions in desired form of light emission. To confirm this possibility, critical distance ( equation:

=2

TE D





) is calculated using the following

!

(3)

Where, V represents unit cell volume, " refers to critical concentration and N depicts the quantity of cationic sites per unit cell. In this work, V = 168.9 Å3, N = 2 and " = 0.03, thus

EP

critical distance of 17.52 Å is estimated with the help of equation 3 suggested by Blasse. Thus, the non-radiative energy transfer possibility through exchange interaction is eliminated in the present case, as critical distance value comes out to be higher than 5Å and the previous reports value must be less than 5Å for energy transfer occurring via exchange

AC C

clearly suggest that

interaction. Now, there is a strong possibility of electric multi-polar interaction to be an appropriate reason for observed concentration quenching phenomenon. Van Uitert stated an equation for computing the intensity of any multi-polar interaction which is based upon variation in emission intensity via emitting level possessing multi-polar interactions [46]. The equation followed by emission intensity per dopant ion (I) is mentioned here #

= $[1 + ' "

8

(/

]

+

(4)

ACCEPTED MANUSCRIPT

Here, x implies dopant composition, Q refers to multi-polar interaction constant having values of 6 (d-d type interaction), 8 (dipole-quadrupole or d-q type interaction) or 10 for quadrupolequadrupole (q-q) type interaction and both K as well as β are constants under the identical

specified below: #

log =

(

− -./"

nanophosphor. The linear relationship among log

#

#

(5)

Vs log x for SrGdAlO4: Sm3+

SC

Where, C is equal to log K – log β. Fig. 10 displays plot of log

RI PT

excitation state for present host lattice system. Equation 4 can be transformed into equation 5 as

and log x is clearly signified by the figure

which provides the slope value of -2.05503. Then Q value is calculated utilizing the slope value #

M AN U

determined via the linear fitting of log

Vs log x plot. The resulted Q value is 6.2 i.e. nearly

equal to 6, indicating the dipole-dipole type electric multi-polar interaction as the major reason for concentration quenching taking place in emission intensity of Sm3+ ions in SrGdAlO4 nanophosphor.

The luminescence decay curves of synthesized SrGd(1-x)SmxAlO4 (x = 0.5 - 15 mol %)

TE D

nanophosphors (shown in Fig. 11) are realized to be fitted by given mono-exponential relation [47].

0 = I2 3"4 −5/6

(6)

EP

Where 6 corresponds to radiative decay time, I and I0 are representing the corresponding photoluminescence intensity at time equal to t and 0 respectively. The inset of Fig. 11 clearly the

logarithmic

AC C

shows

variation

in

normalized

photoluminescence

intensity

of

SrGd0.97Sm0.03AlO4 nanophosphor with varying time. The estimated lifetime values of synthesized SrGd(1-x)SmxAlO4 (x = 0.5 - 15 mol %) nanophosphors are summarized in Table 5 which clearly reveals the decrease in lifetime with increment in dopant concentration. 3.3. Band Gap Analysis DRS of SrGd(1-x)SmxAlO4 (x = 0.5 - 15 mol %) nanophosphors are clearly demonstrated in Fig. 12 which exhibit sharp peaks primarily lie at 407 nm, 378 nm assigned to 6H5/2 → 4K11/2 and 9

ACCEPTED MANUSCRIPT

6

H5/2 → 4D5/2 transitions respectively. The energy band gap (Eg) for optimum composition of

prepared nanophosphor [48,49] i.e. SrGd0.97Sm0.03AlO4 was estimated (~ 5.45 eV) by employing Kubelka-Munk theory [50]. Fig. 13 (a) illustrates the tangent drawn to [αhν]2 versus hν plot for calculation of energy band gap for the host matrix (~ 5.50 eV), whereas Fig. 13 (b) shows band

RI PT

gap for the optimum nanophosphor (SrGd0.97Sm0.03AlO4). The slight drop in band gap value is observed in case of doped sample which is mainly due to creation of additional electronic states by trivalent samarium ions within the band gap of the host lattice. Hence, decrement in energy band gap value upon doping signifies better luminescent features of doped sample. The Kubelka

hν =

Where

∞

+

∞

8 ∞

7

(7)

M AN U

α=

SC

Munk function (α) and Photon energy (hν) are determined with the help of following relations

+8 2

(8)

9

refers to reflection coefficient and : is wavelength used. The additional information

regarding refractive index of doped sample can be obtained using the following relation [51] ;7 +

= 1 − =

TE D

;7 < +

>?

(9)

82

Hence, by evaluating equation 9, refractive index of SrGd0.97Sm0.03AlO4 nanophosphor comes

EP

out nearly equal to 1.682. 3.4. Colorimetric Studies

AC C

CIE 1931 chromaticity coordinates (x, y) were used to determine the luminescent behavior of SrGdAlO4: Sm3+ nanophosphor. MATLAB software computed the CIE coordinates for SrGd(1x)SmxAlO4

(x = 0.5 - 15 mol %) nanophosphors by utilizing their emission spectra recorded at

407 nm excitation wavelength and results are summarized in Table 5 that clearly illustrates the orange-red

emission

via

synthesized

samples.

The

resulted

CIE

coordinates

of

SrGd0.97Sm0.03AlO4 nanophosphor is marked in Fig. 14. Fig. 15 illustrates the comparison of emission intensity of the synthesized optimized nanophosphor (SrGd0.97Sm0.03AlO4) with the emission intensity of a commercial phosphor 10

ACCEPTED MANUSCRIPT

(Y3Al5O12: Ce3+) [42,52]. The reddish orange emission indicates the applications of the synthesized nanophosphors in solid state lighting. 4. Conclusions

RI PT

SrGd(1-x)SmxAlO4 (x = 0.5 - 15 mol %) nanocrystalline phosphors were successfully prepared for the first time via employing solution combustion process after sintering for 3h at 1300˚C. PXRD patterns of synthesized nanophosphors revealed information regarding tetragonal phase and space group (SG) I4/mmm (SG number139). SEM and TEM images confirmed the spherical

SC

morphology and nanocrystalline nature of synthesized phosphor. EDS confirmed the presence of Sr, Gd, Al, O and Sm elements in the prepared nanophosphors. The optimal composition of

M AN U

doped matrix was found to be SrGd0.97Sm0.03AlO4 as a result of concentration quenching phenomenon occurring beyond 3.0 mol % trivalent samarium ion concentration. The exact reason accountable for this quenching in photoluminescence intensity because of increment in dopant ion concentration was dipole-dipole multipolar interactions. The estimated CIE coordinates (0.542, 0.454) evaluated through emission spectra for optimized SrGd0.97AlO4: 0.03 Sm3+ nanophosphor correspond to orange-red color. These synthesized nanophosphors exhibit a

TE D

dominant emission corresponding to 4G5/2 → 6H7/2 (600 nm) transition upon ultraviolet excitation of 407 nm. The band gap analysis from DRS unveiled the Eg and refractive index of SrGd0.97Sm0.03AlO4 nanophosphor as 5.45 eV and 1.682 respectively. The results confirm the potential use of orange red light emitting SrGdAlO4: Sm3+ nanophosphor for near ultraviolet

EP

based pc-WLEDs.

AC C

Acknowledgement

One of the authors, Anju Hooda gratefully thanks the Council of Scientific and Industrial Research (CSIR), New Delhi, India for its funding in the form of junior research fellowship (JRF) (Award No: 09/382(0195)/2017-EMR-I) to accomplish this research work. Authors are also thankful to the University Grant Commission for providing financial support under SAP to the department of chemistry. Conflicts of interest The authors have no conflicts of interest to declare. 11

ACCEPTED MANUSCRIPT

References [1]

R.A. Gilstrap, T. Morris, C.J. Summers, H. Menkara, B.K. Wagner, M. Minkara,

RI PT

Development of nanophosphors for light emitting diodes, Opt. Express. 19 (2011) A972. doi:10.1364/oe.19.00a972. [2]

T.Y. Ohulchanskyy, I. Roy, K.T. Yong, H.E. Pudavar, P.N. Prasad, High-resolution light microscopy using luminescent nanoparticles, Wiley Interdiscip. Rev. Nanomedicine

G. Chen, C. Yang, P.N. Prasad, Nanophotonics and nanochemistry: Controlling the

M AN U

[3]

SC

Nanobiotechnology. 2 (2010) 162–175. doi:10.1002/wnan.67.

excitation dynamics for frequency up- and down-conversion in lanthanide-doped nanoparticles, Acc. Chem. Res. 46 (2013) 1474–1486. doi:10.1021/ar300270y. [4]

F. Soofivand, F. Mohandes, M. Salavati-Niasari, Silver chromate and silver dichromate nanostructures: Sonochemical synthesis, characterization, and photocatalytic properties,

[5]

TE D

Mater. Res. Bull. 48 (2013) 2084–2094. doi:10.1016/j.materresbull.2013.02.025. S. Chahar, R. Devi, M. Dalal, P. Boora, V.B. Taxak, S.P. Khatkar, Structural and photoluminescent analysis in Judd-Ofelt framework of color tunable SrGd2(1-x)Eu2xAl2O7 nanophosphor for white light emitting materials, J. Lumin. 194 (2018) 271–278.

[6]

EP

doi:10.1016/j.jlumin.2017.10.043.

P.K. Jisha, R. Naik, S.C. Prashantha, C.R. Ravikumar, H.P. Nagaswarupa, H.

AC C

Nagabhushana, D.M. Jnaneshwara, Synthesis, Diffuse reflectance, Electrical and Photoluminesence properties of nanocrystalline Eu3+ doped GdAlO3 via Combustion

method, Mater. Today Proc. 4 (2017) 11706–11712. doi:10.1016/j.matpr.2017.09.086.

[7]

S. Ye, F. Xiao, Y.X. Pan, Y.Y. Ma, Q.Y. Zhang, Phosphors in phosphor-converted white

light-emitting diodes: Recent advances in materials, techniques and properties, Mater. Sci. Eng. R Reports. 71 (2010) 1–34. doi:10.1016/j.mser.2010.07.001. [8]

Y.W. Seo, M. Noh, B.K. Moon, J.H. Jeong, H.K. Yang, J.H. Kim, Synthesis and Luminescent Properties of Eu3+ Doped CaGd4O7; Phosphors by Solvothermal Reaction 12

ACCEPTED MANUSCRIPT

Method, J. Nanosci. Nanotechnol. 15 (2015) 8028–8033. doi:10.1166/jnn.2015.11265. [9]

S. Chahar, M. Dalal, R. Devi, A. Khatkar, P. Boora, V.B. Taxak, S.P. Khatkar, Optical analysis of a novel color tunable Ba2Y(1-x)EuxAlO5 nanophosphor in Judd-Ofelt framework

[10]

RI PT

for solid state lighting, J. Lumin. 199 (2018) 442–449. doi:10.1016/j.jlumin.2018.03.039. R. Mohassel, A. Sobhani, M. Goudarzi, M. Salavati-Niasari, Amino acid modified combustion synthesis, characterization and investigation of magnetic, optical and

615–621. doi:10.1016/j.jallcom.2018.04.251. [11]

SC

photocatalytic properties of Gd2CoMnO6 nanostructures, J. Alloys Compd. 753 (2018)

R. Mohassel, A. Sobhani, M. Salavati-Niasari, M. Goudarzi, Pechini synthesis and

M AN U

characteristics of Gd2CoMnO6 nanostructures and its structural, optical and photocatalytic properties, Spectrochim. Acta - Part A Mol. Biomol. Spectrosc. 204 (2018) 232–240. doi:10.1016/j.saa.2018.06.050. [12]

M. Mahdiani, F. Soofivand, F. Ansari, M. Salavati-Niasari, Grafting of CuFe12O19 nanoparticles on CNT and graphene: Eco-friendly synthesis, characterization and activity,

J.

Clean.

Prod.

176

(2018)

1185–1197.

TE D

photocatalytic

doi:10.1016/j.jclepro.2017.11.177. [13]

F. Li, H. Liu, S. Wei, W. Sun, L. Yu, Photoluminescent properties of Eu3+ and Tb3+ codoped Gd2O3 nanowires and bulk materials, J. Rare Earths. 31 (2013) 1063–1068.

[14]

EP

doi:10.1016/S1002-0721(12)60404-9.

H.S. Jang, W. Bin Im, D.C. Lee, D.Y. Jeon, S.S. Kim, Enhancement of red spectral

AC C

emission intensity of Y3Al5O12:Ce3+ phosphor via Pr co-doping and Tb substitution for the

application

to

white

LEDs,

J.

Lumin.

126

(2007)

371–377.

doi:10.1016/j.jlumin.2006.08.093.

[15]

A. Bohre, K. Avasthi, B. Singh, O.P. Shrivastava, Crystallographic evaluation of titanate ceramics as a host structure for immobilization of samarium, Radiochemistry. 56 (2014) 92–97. doi:10.1134/S1066362214010184.

[16]

G.P. Darshan, H.B. Premkumar, H. Nagabhushana, S.C. Sharma, B.D. Prasad, S.C. 13

ACCEPTED MANUSCRIPT

Prashantha, Neodymium doped yttrium aluminate synthesis and optical properties – A blue light emitting nanophosphor and its use in advanced forensic analysis, Dye. Pigment. 134 (2016) 227–233. doi:10.1016/j.dyepig.2016.06.029. V. Sharma, A. Das, V. Kumar, Eu2+, Dy3+ codoped SrAl2O4 nanocrystalline phosphor for

RI PT

[17]

latent fingerprint detection in forensic applications, Mater. Res. Express. 3 (2016) 015004. doi:10.1088/2053-1591/3/1/015004. [18]

P.K. Jisha, S.C. Prashantha, H. Nagabhushana, Luminescent properties of Tb doped

SC

gadolinium aluminate nanophosphors for display and forensic applications, J. Sci. Adv. Mater. Devices. 2 (2017) 437–444. doi:10.1016/j.jsamd.2017.10.001.

S. Singh, S.P. Khatkar, P. Boora, V.B. Taxak, Structural and luminescent properties of Eu3+-doped

GdSrAl3O7

nanophosphor,

doi:10.1007/s10853-014-8176-5. [20]

J.

Mater.

Sci.

49

(2014)

4773–4779.

C.R. García, L.A. Diaz-Torres, J. Oliva, G.A. Hirata, Green EuAlO3:Eu2+ nanophosphor for

applications

in

WLEDs,

Opt.

TE D

doi:10.1016/j.optmat.2014.07.016. [21]

M AN U

[19]

Mater.

(Amst).

37

(2014)

520–524.

A. Mendoud, L. Guerbous, A. Boukerika, B. Boudine, N. Benrekaa, Effect of pH value on structural and photoluminescence properties of Tb3+-doped Lu2O3 nanopowders synthesized

by

sol–gel

route,

Opt.

Mater.

(Amst).

75

(2018)

802–808.

[22]

EP

doi:10.1016/j.optmat.2017.11.048.

S. Zinatloo-Ajabshir, M.S. Morassaei, M. Salavati-Niasari, Facile fabrication of

AC C

Dy2Sn2O7-SnO2 nanocomposites as an effective photocatalyst for degradation and

removal of organic contaminants, J. Colloid Interface Sci. 497 (2017) 298–308. doi:10.1016/j.jcis.2017.03.031.

[23]

S. Zinatloo-Ajabshir, M. Salavati-Niasari, M. Hamadanian, Praseodymium oxide nanostructures: Novel solvent-less preparation, characterization and investigation of their optical

and

photocatalytic

properties,

doi:10.1039/c5ra00817d.

14

RSC

Adv.

5

(2015)

33792–33800.

ACCEPTED MANUSCRIPT

[24]

S. Zinatloo-Ajabshir, M. Salavati-Niasari, Facile route to synthesize zirconium dioxide (ZrO2) nanostructures: Structural, optical and photocatalytic studies, J. Mol. Liq. 216 (2016) 545–551. doi:10.1016/j.molliq.2016.01.062. S.

Zinatloo-Ajabshir,

M.

Salavati-Niasari,

Nanocrystalline

Pr6O11:

Synthesis,

RI PT

[25]

characterization, optical and photocatalytic properties, New J. Chem. 39 (2015) 3948– 3955. doi:10.1039/c4nj02106a. [26]

L.K. Bharat, G.S.R. Raju, J.S. Yu, Red and green colors emitting spherical-shaped

(2017) 1–14. doi:10.1038/s41598-017-11692-1.

T. V. Samulski, P.T. Chopping, B. Haas, Photoluminescent thermometry based on

M AN U

[27]

SC

calcium molybdate nanophosphors for enhanced latent fingerprint detection, Sci. Rep. 7

europium-activated calcium sulphide (hyperthermia application), Phys. Med. Biol. 27 (1982) 107–114. doi:10.1088/0031-9155/27/1/011. [28]

Y. Li, Z. Wang, L. Sun, Z. Wang, S. Wang, X. Liu, Y. Wang, Investigation of oxygen vacancy and photoluminescence in calcium tungstate nanophosphors with different

[29]

TE D

particle sizes, Mater. Res. Bull. 50 (2014) 36–41. doi:10.1016/j.materresbull.2013.10.022. I.M. Pinatti, P.F.S. Pereira, M. de Assis, E. Longo, I.L.V. Rosa, Rare earth doped silver tungstate for photoluminescent applications, J. Alloys Compd. 771 (2019) 433–447.

[30]

EP

doi:10.1016/j.jallcom.2018.08.302.

M. Salavati-Niasari, F. Soofivand, A. Sobhani-Nasab, M. Shakouri-Arani, A. Yeganeh Faal, S. Bagheri, Synthesis, characterization, and morphological control of ZnTiO3

AC C

nanoparticles through sol-gel processes and its photocatalyst application, Adv. Powder Technol. 27 (2016) 2066–2075. doi:10.1016/j.apt.2016.07.018.

[31]

T. Gholami, M. Salavati-Niasari, M. Sabet, Investigate the effect of silica on improvement electrochemical storage of hydrogen in ZnAl2O4 spinel, J. Alloys Compd. 751 (2018) 275–

282. doi:10.1016/j.jallcom.2018.04.021. [32]

T. Gholami, M. Salavati-Niasari, S. Varshoy, Investigation of the electrochemical hydrogen storage and photocatalytic properties of CoAl2O4 pigment: Green synthesis and 15

ACCEPTED MANUSCRIPT

characterization,

Int.

J.

Hydrogen

Energy.

41

(2016)

9418–9426.

doi:10.1016/j.ijhydene.2016.03.144. [33]

A. Salehabadi, M. Salavati-Niasari, F. Sarrami, A. Karton, Sol-Gel auto-combustion

RI PT

synthesis and physicochemical properties of BaAl2O4 nanoparticles; electrochemical hydrogen storage performance and density functional theory, Renew. Energy. 114 (2017) 1419–1426. doi:10.1016/j.renene.2017.07.119. [34]

A. Salehabadi, M. Salavati-Niasari, T. Gholami, Green and facial combustion synthesis of

SC

Sr3Al2O6 nanostructures; a potential electrochemical hydrogen storage material, J. Clean. Prod. 171 (2018) 1–9. doi:10.1016/j.jclepro.2017.09.250.

M. Ayvacikli, A. Ege, N. Can, Radioluminescence of SrAl2O4:Ln3+ (Ln = Eu, Sm, Dy) phosphor

ceramic,

Opt.

doi:10.1016/j.optmat.2011.07.023. [36]

M AN U

[35]

Mater.

(Amst).

34

(2011)

138–142.

Y.C. Li, Y.H. Chang, Y.F. Lin, Y.S. Chang, Y.J. Lin, Synthesis and luminescent properties of Ln3+ (Eu3+, Sm3+, Dy3+)-doped lanthanum aluminum germanate LaAlGe2O7

[37]

TE D

phosphors, J. Alloys Compd. 439 (2007) 367–375. doi:10.1016/j.jallcom.2006.08.269. S. Ekambaram, K.C. Patil, Synthesis and properties of Eu2+ activated blue phosphors, J. Alloys Compd. 248 (1997) 7–12. doi:10.1016/S0925-8388(96)02622-9. A. Okasha, F. Gomaa, H. Elhaes, M. Morsy, S. El-Khodary, A. Fakhry, M. Ibrahim,

EP

[38]

Spectroscopic analyses of the photocatalytic behavior of nano titanium dioxide, Spectrochim. Acta - Part A Mol. Biomol. Spectrosc. 136 (2015) 504–509.

[39]

AC C

doi:10.1016/j.saa.2014.09.063.

G.P. Darshan, H.B. Premkumar, H. Nagabhushana, S.C. Sharma, S.C. Prashantha, H.P. Nagaswarup, B.D. Prasad, Blue light emitting ceramic nano-pigments of Tm3+ doped

YAlO3: Applications in latent finger print, anti-counterfeiting and porcelain stoneware, Dye. Pigment. 131 (2016) 268–281. doi:10.1016/j.dyepig.2016.02.015.

[40]

Z. Fu, S. Zhou, T. Pan, S. Zhang, Preparation and luminescent properties of cubic Eu3+:Y2O3nanocrystals and comparison to bulk Eu3+:Y2O3, J. Lumin. 124 (2007) 213–216. 16

ACCEPTED MANUSCRIPT

doi:10.1016/j.jlumin.2006.02.020. [41]

M. Dalal, V.B. Taxak, S. Chahar, A. Khatkar, S.P. Khatkar, A promising novel orange-red emitting SrZnV2O7:Sm3+ nanophosphor for phosphor-converted white LEDs with nearexcitation,

J.

Phys.

Chem.

Solids.

doi:10.1016/j.jpcs.2015.10.017. [42]

89

(2016)

45–52.

RI PT

ultraviolet

S. Devi, A. Khatkar, V.B. Taxak, M. Dalal, S. Chahar, J. Dalal, S.P. Khatkar, Optical properties of trivalent samarium-doped Ba5Zn4Y8O21 nanodiametric rods excitable by

[43]

SC

NUV light, J. Alloys Compd. 767 (2018) 409–418. doi:10.1016/j.jallcom.2018.07.127. S. Chahar, V.B. Taxak, M. Dalal, S. Singh, S.P. Khatkar, Structural and

M AN U

photoluminescence investigations of Sm3+ doped BaY2ZnO5 nanophosphors, Mater. Res. Bull. 77 (2016) 91–100. doi:10.1016/j.materresbull.2016.01.027. [44]

K.M. Girish, S.C. Prashantha, R. Naik, H. Nagabhushana, Zn2TiO4: A novel host lattice for Sm3+doped reddish orange light emitting photoluminescent material for thermal and fingerprint

sensor,

Opt.

[45]

TE D

doi:10.1016/j.optmat.2017.08.009.

Mater.

(Amst).

73

(2017)

197–205.

G.P. Darshan, H.B. Premkumar, H. Nagabhushana, S.C. Sharma, S.C. Prashanth, B.D. Prasad, Effective fingerprint recognition technique using doped yttrium aluminate nano phosphor

material,

J.

Colloid

Interface

Sci.

464

(2016)

206–218.

[47]

K. Brinkert, Electron transfer, 2018. doi:10.1007/978-3-319-77980-5_4.

AC C

[46]

EP

doi:10.1016/j.jcis.2015.11.025.

M. Xu, W. Zhang, N. Dong, Y. Jiang, Y. Tao, M. Yin, Preparation and characterization of optical spectroscopy of Lu2O3:Eu nanocrystals, J. Solid State Chem. 178 (2005) 477–482.

doi:10.1016/j.jssc.2004.09.003.

[48]

S. Devi, M. Dalal, J. Dalal, A. Hooda, A. Khatkar, V.B. Taxak, S.P. Khatkar, Nearultraviolet excited down-conversion Sm3+-doped Ba5Zn4Gd8O21 reddish-orange emitting nano-diametric

rods

for

white

LEDs,

doi:10.1016/j.ceramint.2019.01.026. 17

Ceram.

Int.

45

(2019)

7397–7406.

ACCEPTED MANUSCRIPT

[49]

P. Biswas, V. Kumar, V. Sharma, A.K. Bedyal, N. Padha, H.C. Swart, Potential of Sm3+ doped LiSrVO4 nanophosphor to fill amber gap in LEDs, Phys. B Condens. Matter. 535 (2018) 221–226. doi:10.1016/j.physb.2017.07.040. C.J. Bodson, S.L. Pirard, R. Pirard, L. Tasseroul, C. Bied, M. Wong Chi Man, B.

RI PT

[50]

Heinrichs, S. D. Lambert, P-Doped Titania Xerogels as Efficient UV-Visible Photocatalysts,

J.

Mater.

Sci.

Chem.

doi:10.4236/msce.2014.28004.

02

(2014)

17–32.

C. Suresh, H. Nagabhushana, G.P. Darshan, R.B. Basavaraj, D. Kavyashree, S.C. Sharma,

SC

[51]

Eng.

A. Arulmozhi, B. Daruka Prasad, H.J. Amith Yadav, Facile LaOF: Sm3+ based labeling

M AN U

agent and their applications in residue chemistry of latent fingerprint and cheiloscopy under UV-visible light, Arab. J. Chem. (2017). doi:10.1016/j.arabjc.2017.09.014. J. Liang, L. Sun, G. Annadurai, B. Devakumar, S. Wang, Q. Sun, J. Qiao, H. Guo, B. Li, X. Huang, Synthesis and photoluminescence characteristics of high color purity Ba3Y4O9:Eu3+red-emitting phosphors with excellent thermal stability for warm W-LED

EP

TE D

application, RSC Adv. 8 (2018) 32111–32118. doi:10.1039/c8ra06129g.

AC C

[52]

18

ACCEPTED MANUSCRIPT

Table 1 Differences among crystal structure data of SrGd0.97Sm0.03AlO4 nanophosphor and standard

SrGdAlO4

SrGd0.97Sm0.03AlO4

Formula weight

335.85

335.64

Symmetry

Tetragonal

Tetragonal

Space group

I4/mmm

I4/mmm

a (Å)

3.697

b (Å)

3.697

c (Å)

12.36

α = β = γ (degree)

90˚

Volume ( Å3)

168.93

Z

2

Density

6.5987

Pearson Code

tI14

Wyckoff Sequence

e2ca

e2ca

SC

Formula

M AN U

RI PT

SrGdAlO4 host matrix.

3.694 (1)

3.694 (1)

12.382 (5) 90˚

169.00 (1) 2

6.5954

TE D

tI14

EP

Table 2.

Different types of atomic parameters and refined atomic positions of SrGd0.97Sm0.03AlO4

AC C

nanophosphor.

Iontype

Site

occupancy x/a

y/b

z/c

Uiso (Å2)

Sm3+

4mm

0.015

0.0

0.0

0.3580

0.025

Gd3+

4mm

0.485

0.0

0.0

0.3580

0.0

Sr2+

4mm

0.5

0.0

0.0

0.3580

0.0

O1

O2-

mmm

1.0

0.0

0.5

0.0

0.0

O2

O2-

4mm

1.0

0.0

0.0

0.1627

0.0

Al1

Al3+

4/mmm

1.0

0.0

0.0

0.0

0.0

Label Sm1 Gd1 Sr1

ACCEPTED MANUSCRIPT

Table 3 Numerous interatomic bond distances (Å) in the crystal structure of SrGd0.97Sm0.03AlO4

distance

Al 1 – O1

1.8471(0) × 2

Al 1 – O1

1.8473(0) × 2

Al 1 – O2

2.0146(1) × 1

Al 1 – O2

2.0150(1) × 1

Sr1/ Gd1/ Sm1 – O2

2.4175(22) × 1

Sr1/ Gd1/ Sm1 – O1

2.5506(15) × 4

M AN U

SC

Bond type

RI PT

nanophosphor.

Sr1/ Gd1/ Sm1 – O2

2.6248(2) × 3

Sr1/ Gd1/ Sm1 – O2

2.6249(2) × 1

TE D

Table 4

Different types of transitions occurring in photoluminescent spectra of SrGd(1-x)SmxAlO4 (x = 0.5 – 15 mol %) nanophosphors.

Type of spectrum

AC C

EP

Nanophosphor

SrGd(1-x)SmxAlO4

Excitation

(x = 0.5 – 15 mol %)

(λem = 600 nm)

Emission (λex = 407 nm)

Transitions

Wave

Intensity

number (cm-1) 6

H5/2 H5/2 6 H5/2 6 H5/2 6 H5/2 6 H5/2 6 H5/2 6 H5/2 6

4

→ → → → → → → →

4

D7/2 F9/2 4 D5/2 6 P7/2 4 K11/2 6 P5/2 + 4M19/2 4 F5/2 + 4I13/2 4 I11/2 +4M15/2 4

G5/2 → 6H5/2 G5/2 → 6H7/2 4 G5/2 → 6H9/2 4

28818 27473 26455 25575 24570 23753 21368 20284

Weak Medium Medium Weak Very Strong Weak Strong Medium

17699 16667 15456

Strong Very Strong Medium

ACCEPTED MANUSCRIPT

Table 5 Estimated Lifetime and CIE values for SrGd1-xSmxAlO4 (x = 0.5 – 15 mol %) nanophosphors. Lifetime (ms)

CIE Coordinates (x,y) 0.532, 0.461 0.541, 0.454 0.542, 0.454 0.531, 0.461 0.529, 0.465 0.519, 0.471

RI PT

SrGd1-xSmxAlO4 (mol %) 0.5 1.0 3.0 5.0 10 15

AC C

EP

TE D

M AN U

SC

1.227 1.151 0.906 0.734 0.575 0.419

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

Fig. 1. X-ray diffraction patterns for SrGd(1-x)SmxAlO4 (x = 0.0 - 15 mol %) nanophosphors sintered at 1300˚C.

Fig. 2. Outcomes of Rietveld refinement over SrGd0.97Sm0.03AlO4 nanophosphor sintered at 1300˚C for 3h; χ2 = 2.266, Rp = 4.68 and wRp = 6.01.

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

(a)

AC C

EP

TE D

Fig. 3. View of unit cell of SrGd0.97Sm0.03AlO4 matrix along with the coordinating environment of various cations.

(b)

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

(c)

(d)

AC C

EP

TE D

Fig. 4. EDS analysis of (a) SrGd0.97Sm0.03AlO4 (optimized sample) (b) SrGd0.85Sm0.15AlO4 nanopowder; (c) SEM and (d) TEM image of SrGd0.97Sm0.03AlO4 nanophosphor sintered at 1300˚C.

Fig. 5. Inspection of PLE spectrum of SrGd0.97Sm0.03AlO4 nanophosphor sintered at 1300˚C for 3h on rooting λem at 600 nm.

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

Fig. 6. Three dimensionally representation of photoluminescence emission spectra of SrGd(1-x)SmxAlO4 (x = 0.5 - 15 mol %) nanophosphors sintered at 1300˚C.

Fig. 7. Portrayal of energy transfer mechanism for SrGdAlO4: Sm3+ nanophosphor.

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

Fig. 8. Variation of intensity ratios at 600 nm and 647 nm with changing Sm3+ concentration.

Fig. 9. Demonstration of variation of emission intensity of SrGd(1-x)SmxAlO4 (x = 0.5 - 15 mol %) nanophosphors with change in Sm3+ concentration.

Fig. 10. Log

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

Vs Log x plot yielding slope of 2.05503 value for SrGdAlO4: Sm3+

AC C

EP

TE D

nanophosphor.

Fig. 11. Depiction of Photoluminescence decay curves for SrGd(1-x)SmxAlO4 (x = 0.5 - 15 mol %) nanophosphors sintered at 1300˚C for 3h and inset is showing fitted curve for 3.0 mol % samarium doped SrGdAlO4 matrix.

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

Fig. 12. Diffuse reflectance spectra of SrGd(1-x)SmxAlO4 (x = 0.5 - 15 mol %) nanophosphors sintered at 1300˚C.

(a)

(b)

Fig. 13. (a) Energy band gap determination of SrGdAlO4 and (b) SrGd0.97Sm0.03AlO4 nanophosphor sintered at 1300˚C using Tauc’s plot.

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

Fig. 14. CIE chromaticity diagram for SrGd0.97Sm0.03AlO4 nanophosphor sintered at 1300˚C.

Fig. 15. Comparison of emission intensities of (SrGd0.97Sm0.03AlO4) and commercial phosphor (YAG: Ce3+).

optimized

nanophosphor

ACCEPTED MANUSCRIPT

Highlights:

RI PT

SC M AN U

•

TE D

•

EP

•

Urea assisted solution combustion technique was utilized to synthesize SrGdAlO4: Sm3+ nanophosphor for the first time. Crystal structure analysis of synthesized nanocrystalline phosphors was carried out in detail. Energy band gap and refractive index for the optimized nanophosphor were estimated successfully. CIE coordinates confirm the characteristic reddish-orange emission and applications of synthesized nanophosphor for pc-WLEDs.

AC C

•