- Email: [email protected]
Morphology control synthesis and photoluminescence of yttrium orthophosphate microstructures
Accepted Manuscript Morphology control synthesis and photoluminescence of yttrium orthophosphate microstructures Heikham Farida Devi, Thiyam David Singh PII: DOI: Reference:
S0167-577X(18)31154-6 https://doi.org/10.1016/j.matlet.2018.07.143 MLBLUE 24709
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
19 June 2018 24 July 2018 25 July 2018
Please cite this article as: H.F. Devi, T.D. Singh, Morphology control synthesis and photoluminescence of yttrium orthophosphate microstructures, Materials Letters (2018), doi: https://doi.org/10.1016/j.matlet.2018.07.143
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.
Morphology control synthesis and photoluminescence of yttrium orthophosphate microstructures Heikham Farida Devi[a] and Thiyam David Singh[a] * Department of Chemistry, National Institute of Technology Manipur, Langol Manipur-795004, India Email: [email protected]
Abstract A facile, simple route for modifying the structural and morphological architecture of trivalent europium ion doped yttrium orthophosphates through pH tuning is described. SEM analysis confirmed the evolution of different architectural morphology through pH tuning. Additionally, the possible mechanism for the selective control of the phase structure and morphological evolution of YPO 4:5 Eu3+ was well ascertained. The results strongly augmented that the control phase transformation from hexagonal to tetragonal structure presented a remarkable changes in luminescent properties. This change was rationally evaluated, and the influence of the phase and shape on optical properties was well explored. It hints that we can synthesize multi-functional materials by controlling the shape and structure of yttrium orthophosphates. Keywords: structural, phase transformation, multi-functional, pH tuning.
1
Introduction It is well known that the synthesis pathways being an important route for ensuing novel and fruitful properties for multifunctional materials. At present, many researchers have witnessed and participated in investigation of significant promises and speculation on the impact of phase composition and architectural morphology of nanoparticles. [1-4] Conversely, synthesis duration was found to have prominent influence on the tailoring of new functional nano scale materials as well. Vanetsev and co-workers, [5] reported the synthesis of YPO4 nanoparticles with various phase composition and morphology, and Li and co-workers, [6] demonstrated rational tunability of the phases and shape of YPO 4 by Ln3+ (Ln3+ = Tb, Eu, Dy) and V5+ doping. Also, an outlook of lanthanide doped phosphor materials in the past, present and future evaluated their especial niche in realms of bio-probe and optoelectronics applications. [7-8] Nonetheless, there have been scarce systematic reports focussing on this subject hitherto, so it remains a large space for an expeditious expansion of research work. Herein, in the light of beneficial use of venerable phosphors with variable phase composition and morphology, this report aims to explore different phase composition with alterable morphology promoted by different duration of reaction time on pH adjustment unlike other reports which involved different stoichiometric ratio of Y3+ and PO43- and variable pH value. [6, 8] It has been manifested that using trivalent europium (Eu3+) ions to substitute for trivalent yttrium (Y3+) ions in YPO4 crystals allows product with uneven phase composition and morphology to be easily modified into uniform particles with different shapes in the solution system. The plausible mechanism is as follows: each addition of NaOH (5 mmol) to the growth suspension, the H+ were partially neutralized, and the localization of such H+ ions in the grain surface developed surface free energies of the various crystallographic phases differing considerably. [9] It is further proved that this growth strategy would be faster for those facets having higher free energy, which develops the possibility of hampering the natural growth habit of the crystals and affords additional modulation of the growth anisotropy. Materials and method For the synthesis of YPO4:5 Eu3+, stoichiometric Y2(CO3)3.xH2O and Eu2O3 were dissolved in 2 ml of conc. HCl in a 250 ml round-bottom flask. Excess acid was evaporated at least three times by adding 10 ml of double distilled water. Chlorides of Y3+ and Eu3+ formed were mixed with 0.3915 mg of NH4H2PO4. 100 ml of ethylene glycol was added to the above mixture and maintained pH at 5, 6 and 7 by adding freshly prepared 5 mmol of NaOH solution and heated the above solution for 1.5, 2 and 3 hours at 180ºC respectively. The resulting white milky precipitate formed was removed by centrifugation at 1000
2
rpm for 15 min, washed several times with methanol to remove excess ethylene glycol and then dried at room temperature overnight.
Results and Discussion The selection of yttrium orthophosphates as the doping host lattice was motivated by their low phonon frequencies, which enhance retardation of non- radiative losses, which further improves the optical properties of the nanocrystals. [10] The recorded SEM images clearly confirmed that YPO4 crystals fabricated at pH 5 and 1.5 hours duration had a bimodal distribution i.e., some irregular agglomerated small particles, while others were large enough with dumbbell shape. However, after increasing pH value and reaction time, the size distribution and the architectural morphology of the yttrium orthophosphate crystals were remarkably changes. As shown in Figure 1b and 1c, the monodisperse Eu 3+- doped YPO4 5 3 m (pH = 7 and 3 hours). Further, the incorporation of Eu 3+ ions into the YPO4 crystals was justified by EDAX (Figure 1d). Noteworthy, characterization via X-ray diffraction pattern displays the pure hexagonal and tetragonal phase with no other phases or impurities detected, which further substantiates the experimental proof of the crystalline nature of the ensuing YPO 4 particles. Astonishingly, the FTIR spectra display clearly the difference between the stretching bands of PO43group (Figure S2). Moreover, the XRD patterns of the samples are well index with that of standard hexagonal and tetragonal YPO4 (JCPDS card no. 42-0082 & 11-0254) respectively ( Figure S1). Further, the diffraction pattern of YPO4.0.8H2O prepared at pH 5 consists two sets of diffraction peaks: one is of low intensity on comparing with reference card, ascribed to irregular agglomerated seeds while the other is of such intense with reference card and corresponds to dumbbell seeds verifying the bimodal distribution of the particles. In contrast, the diffraction pattern of the samples ensuing at pH 6 and 7 exhibits only one set of comparable intense peak with the reference card, substantially indicating the uniform particle distribution, in agreement with the SEM observations. In addition, UV- Visible absorption spectra of the prepared t-YPO4:5 Eu3+ and h-YPO4.0.8H2O:5 Eu3+ particles exhibit broad peaks with maxima at 250 and 280 nm, respectively (Figure S3). These arise due to presence of defects and grain boundaries in particles and these induce the trap levels below conduction band of YPO 4 [16, 17]. It is to be noted that pure YPO4 has a band gap of 8.6 eV (155 – 137 nm), which is more than that of trap levels absorption [10]. Defects may arise from imperfection in lattice due to difference in grain boundaries or doping of Eu3+ ions in Y3+ sites. YPO4.0.8 H2O shows the red shift in absorption band as
3
compared to t-YPO4 and this may arise from the presence of deep traps in conduction band of insulator/semiconductor. Remarkably, the evolution of the diffraction peaks for YPO 4:5 Eu3+ (Figure S1), represents that the intensity of the (102) diffraction planes enhanced while tuning the pH value at 6 and the respective peak totally diminished when the pH value reached 7. SEM observation (Figure 1) enlightened the proof that the sizes of those crystals are gradually enhanced and particle size distribution embodied to be more homogeneous with increasing pH value. Concretely speaking, to ensure the tailoring of monodisperse YPO4 crystals in the pure phase, the highest pH value was found to be 7. The possible schematic mechanism on the modification of size and shape of the YPO 4 microcrystals is illustrated in Scheme 1. In the growing precipitation system, organic additives behaving as surfactants can modify the order of free energies of various facets after interacting with metal ion surfaces. This change may undoubtedly affect the growing rates of different facets of the crystals. [11] In present case, environmentally benign ethylene glycol is added, which can easily coordinated with Y 3+ ions. When the reaction process is prolonged, YPO4 nuclei grow quickly into hexagonal phase, benefitting from OH released from the precipitating system to the microcrystals, like the situation reported for the growth of NaYF4 nuclei. [12] When Eu3+ ions are introducing into the system, they substituted Y3+ sites. Continuing reaction time, stabling charge balance between the reactants, growth of crystals became dominant and architectures compost of mixture of small agglomerated irregular and microdumbbells were formed. As the reaction process further continued, the small agglomerated architectures grew larger and the morphology transformed to dumbbells under the influence of the surface energy created. While enhancing the reaction time further with increasing pH value, the architectures again transformed into microrods. Again, it is noteworthy that the crystal growth environment and the nature of crystal structure like degree of supersaturation, reaction diffusion, and surface energy, subsequently determine the crystal growth and the final product shape. [13] Besides, it is very interesting that the switches of crystal growth habit is seem to be closely related to the relative order of the surface energies created in the reaction system. [14] Generally, the rate of crystal growth will occur in the perpendicular direction of face with higher surface energy, which further reduced the higher surface energies and enhance the lower surface energies in area. [15] For microdumbbells, the surrounding edges are having higher surface energy than the central area of the crystal, so that the growth of the crystals mainly occurs on the edge of the particles. Similarly, the formation of microrods architectures is also due to the existence of the surface energy while edge sharping and the crystal growth rates in different edge direction would be profoundly affected. In addition, the microparticles augment significantly (0.6 m in diameter and 3.5 m in height) indicating that the horizontal and vertical growth of the microcrystals with the aging of the precipitating system. 4
Under 394 nm excitation, these YPO4 microcrystals doped with Eu3+ ions exhibit dominant red emission ascribed to 5D0 7F2 transitions of Eu3+(Figure 3). On comparing the emission intensity of hexagonal phase YPO4.0.8 H2O:5 Eu3+, the regular h-YPO4.0.8H2O:Eu3+ microdumbbells are expected for higher emission intensity than the irregular particles. Additionally, t-YPO4:5 Eu3+microrods are showing enhanced emission, which may be decided by the dimension of the crystal growth. The transient dipole field is not only validating by the orientation and permittivity constants of the host materials but also their architectures. We can strongly suggest that the architectural variations influenced the ionic dipole field and, thereby, the emission intensity. Apart from the emission intensity, these microparticles exhibit shifting of the absorption bands towards the lower energy (Figure S3), which is due to presence of more defects.
Conclusions In summary, this study has presented a simple facile route for modifying structure and architectural shape of Eu3+ doped yttrium orthophosphates through aging of the reaction system and changing pH value. These microparticles exhibit potential applications in fluorescent probes i.e., tunable emissions, making them potentially applicable of doped insulator materials in the biological field. The preparation strategy, which involves pH tuning corresponding to aging of precipitating system, might be useful for maintaining the growth of the solution system of some biologically or technologically important materials.
Acknowledgements We thanks USIC, BBAU, Lucknow for providing SEM and EDAX facility. One of the authors (Heikham Farida Devi) thanks to MHRD, New Delhi for financial support as a fellowship.
5
References [1] F. Zhang, et al. J. Am. Chem. Soc. 132 (2010) 2850 [2] V. Mahalingam, et al. AdV. Mater. 21(2009) 4025 [3] M. N. Luwang, et al. J. Am. Chem. Soc. 132 (2010) 2759 [4] Y. P. Du, et al. J. Am. Chem. Soc. 131 (2009) 16364 [5] A.S. Vanetsev, et al. J. All. Compds. 639 (2015) 415 [6] C. Li, et al. Chem. Mater. 21 (2009) 4598-4607 [7] H. Farida, Th. David, Chemistryselect, 2 (2017)10010-1001 [8] C. Li, et al. J. Phys. Chem. C. 113 (2009) 2332-2339 [9] H. Z. Zhang, et al. Nature, 424 (2003) 1025 [10] R. S. Ningthoujam, et al. RSC Adv. 5(2015) 68234 [11] A. R. Tao, et al. Small, 4 (2008) 310 [12] F. Wang, et al. Nature, 463 (2010) 1061 [13] M.Yang, et al. CrystEngComm, 12 (2010) 4141–4145 [14] J. W. Mullin, Crystallization, Butterworths, London 1971. [15] H. E. Buckley, Crystal Growth, Wiley, New York 1951. [16] B. B. Straumal, et al. Beilstein J. Nanotechnol. 7 (2016) 1936 [17] B. B. Straumal, et al. Phys. Status Solidi B 248 (2011) 1581
6
List of figures
Figure1 SEM image of YPO4:5 Eu3+ synthesized at (a) pH = 5, (b) pH = 6, (c) pH = 7 and (d) Edax spectrum.
Figure 2 Schematic illustration of the modifications of various pH values on the size and morphology of YPO4:5 Eu3+
7
Figure 2
.
Figure 3 Excitation and emission spectra of YPO4:5Eu3+ particles.
8
Graphical abstract
9
Highlights: 1. The synthesis technique utterly excludes the usage of any harmful chemicals. 2. Low pH value and reaction temperature leads to bimodal distribution of the particles. 3. By tuning the reaction parameters, transform the crystal structure and architectural morphology.
10
S0167-577X(18)31154-6 https://doi.org/10.1016/j.matlet.2018.07.143 MLBLUE 24709
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
19 June 2018 24 July 2018 25 July 2018
Please cite this article as: H.F. Devi, T.D. Singh, Morphology control synthesis and photoluminescence of yttrium orthophosphate microstructures, Materials Letters (2018), doi: https://doi.org/10.1016/j.matlet.2018.07.143
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.
Morphology control synthesis and photoluminescence of yttrium orthophosphate microstructures Heikham Farida Devi[a] and Thiyam David Singh[a] * Department of Chemistry, National Institute of Technology Manipur, Langol Manipur-795004, India Email: [email protected]
Abstract A facile, simple route for modifying the structural and morphological architecture of trivalent europium ion doped yttrium orthophosphates through pH tuning is described. SEM analysis confirmed the evolution of different architectural morphology through pH tuning. Additionally, the possible mechanism for the selective control of the phase structure and morphological evolution of YPO 4:5 Eu3+ was well ascertained. The results strongly augmented that the control phase transformation from hexagonal to tetragonal structure presented a remarkable changes in luminescent properties. This change was rationally evaluated, and the influence of the phase and shape on optical properties was well explored. It hints that we can synthesize multi-functional materials by controlling the shape and structure of yttrium orthophosphates. Keywords: structural, phase transformation, multi-functional, pH tuning.
1
Introduction It is well known that the synthesis pathways being an important route for ensuing novel and fruitful properties for multifunctional materials. At present, many researchers have witnessed and participated in investigation of significant promises and speculation on the impact of phase composition and architectural morphology of nanoparticles. [1-4] Conversely, synthesis duration was found to have prominent influence on the tailoring of new functional nano scale materials as well. Vanetsev and co-workers, [5] reported the synthesis of YPO4 nanoparticles with various phase composition and morphology, and Li and co-workers, [6] demonstrated rational tunability of the phases and shape of YPO 4 by Ln3+ (Ln3+ = Tb, Eu, Dy) and V5+ doping. Also, an outlook of lanthanide doped phosphor materials in the past, present and future evaluated their especial niche in realms of bio-probe and optoelectronics applications. [7-8] Nonetheless, there have been scarce systematic reports focussing on this subject hitherto, so it remains a large space for an expeditious expansion of research work. Herein, in the light of beneficial use of venerable phosphors with variable phase composition and morphology, this report aims to explore different phase composition with alterable morphology promoted by different duration of reaction time on pH adjustment unlike other reports which involved different stoichiometric ratio of Y3+ and PO43- and variable pH value. [6, 8] It has been manifested that using trivalent europium (Eu3+) ions to substitute for trivalent yttrium (Y3+) ions in YPO4 crystals allows product with uneven phase composition and morphology to be easily modified into uniform particles with different shapes in the solution system. The plausible mechanism is as follows: each addition of NaOH (5 mmol) to the growth suspension, the H+ were partially neutralized, and the localization of such H+ ions in the grain surface developed surface free energies of the various crystallographic phases differing considerably. [9] It is further proved that this growth strategy would be faster for those facets having higher free energy, which develops the possibility of hampering the natural growth habit of the crystals and affords additional modulation of the growth anisotropy. Materials and method For the synthesis of YPO4:5 Eu3+, stoichiometric Y2(CO3)3.xH2O and Eu2O3 were dissolved in 2 ml of conc. HCl in a 250 ml round-bottom flask. Excess acid was evaporated at least three times by adding 10 ml of double distilled water. Chlorides of Y3+ and Eu3+ formed were mixed with 0.3915 mg of NH4H2PO4. 100 ml of ethylene glycol was added to the above mixture and maintained pH at 5, 6 and 7 by adding freshly prepared 5 mmol of NaOH solution and heated the above solution for 1.5, 2 and 3 hours at 180ºC respectively. The resulting white milky precipitate formed was removed by centrifugation at 1000
2
rpm for 15 min, washed several times with methanol to remove excess ethylene glycol and then dried at room temperature overnight.
Results and Discussion The selection of yttrium orthophosphates as the doping host lattice was motivated by their low phonon frequencies, which enhance retardation of non- radiative losses, which further improves the optical properties of the nanocrystals. [10] The recorded SEM images clearly confirmed that YPO4 crystals fabricated at pH 5 and 1.5 hours duration had a bimodal distribution i.e., some irregular agglomerated small particles, while others were large enough with dumbbell shape. However, after increasing pH value and reaction time, the size distribution and the architectural morphology of the yttrium orthophosphate crystals were remarkably changes. As shown in Figure 1b and 1c, the monodisperse Eu 3+- doped YPO4 5 3 m (pH = 7 and 3 hours). Further, the incorporation of Eu 3+ ions into the YPO4 crystals was justified by EDAX (Figure 1d). Noteworthy, characterization via X-ray diffraction pattern displays the pure hexagonal and tetragonal phase with no other phases or impurities detected, which further substantiates the experimental proof of the crystalline nature of the ensuing YPO 4 particles. Astonishingly, the FTIR spectra display clearly the difference between the stretching bands of PO43group (Figure S2). Moreover, the XRD patterns of the samples are well index with that of standard hexagonal and tetragonal YPO4 (JCPDS card no. 42-0082 & 11-0254) respectively ( Figure S1). Further, the diffraction pattern of YPO4.0.8H2O prepared at pH 5 consists two sets of diffraction peaks: one is of low intensity on comparing with reference card, ascribed to irregular agglomerated seeds while the other is of such intense with reference card and corresponds to dumbbell seeds verifying the bimodal distribution of the particles. In contrast, the diffraction pattern of the samples ensuing at pH 6 and 7 exhibits only one set of comparable intense peak with the reference card, substantially indicating the uniform particle distribution, in agreement with the SEM observations. In addition, UV- Visible absorption spectra of the prepared t-YPO4:5 Eu3+ and h-YPO4.0.8H2O:5 Eu3+ particles exhibit broad peaks with maxima at 250 and 280 nm, respectively (Figure S3). These arise due to presence of defects and grain boundaries in particles and these induce the trap levels below conduction band of YPO 4 [16, 17]. It is to be noted that pure YPO4 has a band gap of 8.6 eV (155 – 137 nm), which is more than that of trap levels absorption [10]. Defects may arise from imperfection in lattice due to difference in grain boundaries or doping of Eu3+ ions in Y3+ sites. YPO4.0.8 H2O shows the red shift in absorption band as
3
compared to t-YPO4 and this may arise from the presence of deep traps in conduction band of insulator/semiconductor. Remarkably, the evolution of the diffraction peaks for YPO 4:5 Eu3+ (Figure S1), represents that the intensity of the (102) diffraction planes enhanced while tuning the pH value at 6 and the respective peak totally diminished when the pH value reached 7. SEM observation (Figure 1) enlightened the proof that the sizes of those crystals are gradually enhanced and particle size distribution embodied to be more homogeneous with increasing pH value. Concretely speaking, to ensure the tailoring of monodisperse YPO4 crystals in the pure phase, the highest pH value was found to be 7. The possible schematic mechanism on the modification of size and shape of the YPO 4 microcrystals is illustrated in Scheme 1. In the growing precipitation system, organic additives behaving as surfactants can modify the order of free energies of various facets after interacting with metal ion surfaces. This change may undoubtedly affect the growing rates of different facets of the crystals. [11] In present case, environmentally benign ethylene glycol is added, which can easily coordinated with Y 3+ ions. When the reaction process is prolonged, YPO4 nuclei grow quickly into hexagonal phase, benefitting from OH released from the precipitating system to the microcrystals, like the situation reported for the growth of NaYF4 nuclei. [12] When Eu3+ ions are introducing into the system, they substituted Y3+ sites. Continuing reaction time, stabling charge balance between the reactants, growth of crystals became dominant and architectures compost of mixture of small agglomerated irregular and microdumbbells were formed. As the reaction process further continued, the small agglomerated architectures grew larger and the morphology transformed to dumbbells under the influence of the surface energy created. While enhancing the reaction time further with increasing pH value, the architectures again transformed into microrods. Again, it is noteworthy that the crystal growth environment and the nature of crystal structure like degree of supersaturation, reaction diffusion, and surface energy, subsequently determine the crystal growth and the final product shape. [13] Besides, it is very interesting that the switches of crystal growth habit is seem to be closely related to the relative order of the surface energies created in the reaction system. [14] Generally, the rate of crystal growth will occur in the perpendicular direction of face with higher surface energy, which further reduced the higher surface energies and enhance the lower surface energies in area. [15] For microdumbbells, the surrounding edges are having higher surface energy than the central area of the crystal, so that the growth of the crystals mainly occurs on the edge of the particles. Similarly, the formation of microrods architectures is also due to the existence of the surface energy while edge sharping and the crystal growth rates in different edge direction would be profoundly affected. In addition, the microparticles augment significantly (0.6 m in diameter and 3.5 m in height) indicating that the horizontal and vertical growth of the microcrystals with the aging of the precipitating system. 4
Under 394 nm excitation, these YPO4 microcrystals doped with Eu3+ ions exhibit dominant red emission ascribed to 5D0 7F2 transitions of Eu3+(Figure 3). On comparing the emission intensity of hexagonal phase YPO4.0.8 H2O:5 Eu3+, the regular h-YPO4.0.8H2O:Eu3+ microdumbbells are expected for higher emission intensity than the irregular particles. Additionally, t-YPO4:5 Eu3+microrods are showing enhanced emission, which may be decided by the dimension of the crystal growth. The transient dipole field is not only validating by the orientation and permittivity constants of the host materials but also their architectures. We can strongly suggest that the architectural variations influenced the ionic dipole field and, thereby, the emission intensity. Apart from the emission intensity, these microparticles exhibit shifting of the absorption bands towards the lower energy (Figure S3), which is due to presence of more defects.
Conclusions In summary, this study has presented a simple facile route for modifying structure and architectural shape of Eu3+ doped yttrium orthophosphates through aging of the reaction system and changing pH value. These microparticles exhibit potential applications in fluorescent probes i.e., tunable emissions, making them potentially applicable of doped insulator materials in the biological field. The preparation strategy, which involves pH tuning corresponding to aging of precipitating system, might be useful for maintaining the growth of the solution system of some biologically or technologically important materials.
Acknowledgements We thanks USIC, BBAU, Lucknow for providing SEM and EDAX facility. One of the authors (Heikham Farida Devi) thanks to MHRD, New Delhi for financial support as a fellowship.
5
References [1] F. Zhang, et al. J. Am. Chem. Soc. 132 (2010) 2850 [2] V. Mahalingam, et al. AdV. Mater. 21(2009) 4025 [3] M. N. Luwang, et al. J. Am. Chem. Soc. 132 (2010) 2759 [4] Y. P. Du, et al. J. Am. Chem. Soc. 131 (2009) 16364 [5] A.S. Vanetsev, et al. J. All. Compds. 639 (2015) 415 [6] C. Li, et al. Chem. Mater. 21 (2009) 4598-4607 [7] H. Farida, Th. David, Chemistryselect, 2 (2017)10010-1001 [8] C. Li, et al. J. Phys. Chem. C. 113 (2009) 2332-2339 [9] H. Z. Zhang, et al. Nature, 424 (2003) 1025 [10] R. S. Ningthoujam, et al. RSC Adv. 5(2015) 68234 [11] A. R. Tao, et al. Small, 4 (2008) 310 [12] F. Wang, et al. Nature, 463 (2010) 1061 [13] M.Yang, et al. CrystEngComm, 12 (2010) 4141–4145 [14] J. W. Mullin, Crystallization, Butterworths, London 1971. [15] H. E. Buckley, Crystal Growth, Wiley, New York 1951. [16] B. B. Straumal, et al. Beilstein J. Nanotechnol. 7 (2016) 1936 [17] B. B. Straumal, et al. Phys. Status Solidi B 248 (2011) 1581
6
List of figures
Figure1 SEM image of YPO4:5 Eu3+ synthesized at (a) pH = 5, (b) pH = 6, (c) pH = 7 and (d) Edax spectrum.
Figure 2 Schematic illustration of the modifications of various pH values on the size and morphology of YPO4:5 Eu3+
7
Figure 2
.
Figure 3 Excitation and emission spectra of YPO4:5Eu3+ particles.
8
Graphical abstract
9
Highlights: 1. The synthesis technique utterly excludes the usage of any harmful chemicals. 2. Low pH value and reaction temperature leads to bimodal distribution of the particles. 3. By tuning the reaction parameters, transform the crystal structure and architectural morphology.
10