Judd-Ofelt itemization and influence of energy transfer on Sm3+ ions activated B2O3–ZnF2–SrO–SiO2 glasses for orange-red emitting devices
Introduction
Over the preceding decade, the lanthanide ions have been fascinated scientists when doped with glasses/phosphors owing to their extraordinary usage in solar cells, memory devises, lasing action, w-LEDs, fiber amplification, etc. [[1], [2], [3], [4]]. Further, the simple synthesis procedure makes it an attractive point of course and therefore, this is extensively studied and devised by various researchers. Furthermore, both the host and activator ion concentration can influence the emission possessions of activator to get the desired output. It has been observed that the glasses activated with lanthanides are much superior to crystalline/phosphors owing to its discrete features like less production cost, good chemical and thermal stability, easy fabrication technique, less period to form structures, etc. [5,6]. Besides, the epoxy resin associated with phosphors for white-light emitting devices (w-LEDs) makes it depreciate at high temperatures and high energy excitation sources which strongly lowers the output. Conversely, in glasses, epoxy resin is not present and output cannot be affected at high temperatures [7]. Nowadays, w-LEDs are in trend and replacing conversational lighting sources owing to their energy-saving tendency, ecologically pleasant nature and long lifespan [8]. The w-LEDs are fabricated using the combination of YAG:Ce phosphor mixed with InGaN blue LED. Nevertheless, the w-LEDs are having some drawbacks, like deficiency of red constituent which results in small color rendering index (CRI) and halo effect [9]. To resolve this problem an amalgamation of RGB phosphors as well as, n-UV based LEDs might be inspected to improve the CRI [10]. Though, the tactic meets some shortcomings like low efficiency of the red constituent (Eu3+ activated Y2O2S phosphor) which is merely around 1/8th part of green (Cu+/Al3+ activated ZnS phosphor)/blue constituent (Eu2+ activated BaMgAl10O17 phosphor). Further, an additional possibility of fabricating w-LED is cyan color along with orange-red emitter pumped with n-UV light. Reports suggest that reasonably less work has been done in this track [[9], [10], [11]]. This encouraged us to pick up the PL investigations on Sm3+ activated B2O3–ZnF2–SrCO3–SiO2 glasses for solid-state lighting technology (SSL). In addition to their major part in SSL application, orange-red color-producing glasses exhibit essential evidence linked with lasing possessions like radiative parameters (branching ratio, radiative lifetime, transition probability, etc.). Hence, the expansion of orange-red luminescence producing glasses pumped with n-UV excitation wavelength is highly essential for w-LEDs and lasing action too.
It is obvious from earlier reported work that, borates (B2O3) are well-known glass formers owing to its outstanding characteristics for instance increased transparency along with chemical durability, low fabrication charge as well as melting point, and easy manufacture procedure [12,13]. There are two kinds of coordination of boron atoms in B2O3 glasses which enable its structure more fascinating. The BO3 triangles can make different combinations of borates such as di, tri, tetra and penta through the introduction of appropriate modifier and linked by B–O–B linkages [14,15]. This in-turn consequences in 3-D interconnected networks.
Besides the above said prominent characteristics, B2O3 is having one disadvantage of high phonon energies i.e., 1300 cm−1 and suppresses radiative emissions. The reduced radiative emission can be enhanced by adding some heavy metal oxides into B2O3 [8,14,15]. Therefore, ZnF2 is added, and B2O3–ZnF2 can improve radiative emission. The ZnF2 is having dual character and depending upon the concentration it can act as either network former or network modifier [16]. The introduction of SiO2 into B2O3 can enhance the thermal and mechanical stability. Further, much active covalent bond between B–O–Si, B–O and Si–O as well as less coordination of borate and silicate atom is accountable for the stability of the as-quenched glasses [17].
The fluoride ions associated with borates can possess narrow emission and escalates emission efficiency. Further, it can assist in the elimination of OH ligand from the B2O3 matrix and diminishes the phonon energy of the B2O3 matrix [8,16,17]. The SrCO3 can influence physical possessions of the host matrix, acts as a modifier and enhance host chemical durability. Further, glasses containing SrCO3 can enhance the glass creating stability and reduce the coefficient of expansion [18,19]. All the aforesaid technical supports presented by B2O3, ZnF2, SrCO3, SiO2 encouraged us to organize a noble glassy matrix viz. Zinc Strontium fluoro borosilicate (ZSFBSi) glass to investigate its appropriateness as a luminescent candidate for SSL technology.
The 4f→4f/4f→5d emission transitions in lanthanides are responsible for luminescence properties. Midst all, the samarium ion (Sm3+) attracted researchers due to its application in color displays, beneath sea communication, optical storage, orange-red lasing action, optoelectronic gadgets, etc. [20,21]. It is evident from the literature that Sm3+ can behave either sensitizer or activator. The energy transfer (ET) process encountered between sensitizer and activator present in a host glass may be dipole-dipole (D-D) or dipole-quadrupole (D-Q) or quadrupole-quadrupole (Q-Q) in nature. The PL spectra of Sm3+ ions exposes an intense greenish-yellow, orange-red, light red and red ascribed to 4G5/2 → 6H5/2, 6H7/2, 6H9/2, 6H11/2 transitions, respectively. Additionally, Sm3+ activated high energy lasers are being used in Microbeam Radiation Therapy for cancer treatment [22].
Recently, Kirdsiri et al. studied the optical as well as luminescence possessions of Sm3+ activated lithium borate glasses using altered modifier oxides [10]. They observed that under 403 nm excitation wavelength, the aforesaid glasses were revealing strong orange emission and applicable for w-LEDs. Rani et al. investigated the structural, optical and PL properties of Sm3+ activated BaPbAlFB glasses and found that the suitability of these glasses in optoelectronic device applications [15]. K. Jha and co-workers detected ET mechanism in phosphate glasses co-doped with Tb3+/Sm3+ for SSL applications. They have observed good ET efficiency of around 41.18% for TS05 glass [7]. Furthermore, Paz et al. investigated the up and down-conversion of Er3+-to-Sm3+ doped TeO2–ZnO glasses. They observed that the ET pathway powerfully relies on the pumping wavelength and ET track which is further a key for w-LEDs [23]. Currently, few researchers are working on an associative study of ET, absorption, PL in correlation with J-O analysis and no one has investigated these possessions in Sm3+ activated B2O3–ZnF2–SrCO3–SiO2 (ZSFBSi) glass. Therefore, the present paper reports a systematized study of ZSFBSi glasses doped with varying content of Sm3+ using XRD, UV–vis–NIR Spectrometer and PL spectrometer characterization tools to investigate the photonic properties for w-LEDs, lasers and fiber application.
Section snippets
Sample synthesis
ZSFBSi glasses doped with varying concentrations of Sm3+ ions were synthesized via melt quench method taking a suitable quantity of high purity (99.99%) analar grade chemicals like H3BO3, ZnF2, SrCO3, SiO2, and Sm2O3. All the constituent raw chemical was crushed into smooth powder to get a uniform mixture. The uniform mixture kept into an alumina crucible was then fired at 1050 °C in a high-temperature furnace for 4 h. The fired melt was poured in a brass plate having temperature 350 °C (fired
XRD of as-quenched glasses
With a view to know about the amorphous behavior of as-quenched glasses, the XRD spectra are monitored. Fig. 1 displays the XRD spectra of the as-quenched un-doped ZSFBSi glass, ZSFBSiSm1.0 and ZSFBSiSm2.0 glass. The XRD spectra of the as-quenched glasses are similar except variation in intensity. The wide hump in XRD approves the non-crystalline behavior of as-quenched glasses.
FT-IR spectral analysis of as-quenched glasses
The FT-IR spectroscopy is a very fundamental technique for finding the presence of different functional groups
Conclusions
In summary, Sm3+ doped ZSFBSi glasses are synthesized via the traditional melt quench method to cognize their luminescence character. The XRD of the as-quenched glasses were recorded to identify the non-crystalline nature of the same. The ionic bonding between Sm3+ ion and oxygen anion was confirmed through absorption spectral analysis. The results obtained from J-O intensity parameters i.e., the lesser value of Ω2 parameter re-confirmed the ionic nature of bonding parameters. Under 402 nm
Credit author statement
Ravina: Data curation, Writing - original draft. Naveen: Data curation, Writing - original draft. Sheetal: Formal analysis. V. Kumar: Formal analysis. S. Dahiya: Resources. Nisha Deopa: Supervision, Validation, Writing - review & editing. R. Punia: Supervision, Validation, Writing - review & editing. A.S.Rao: Resources, Writing - review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The corresponding authors, Dr. Nisha Deopa and Prof. Rajesh Punia are thankful to Prof. R.B. Solanki, Hon'ble Vice-Chancellor, Chaudhary Ranbir Singh University, Jind, Haryana for his unconditional support, help and encouragement. One of the authors, Prof. A.S. Rao is grateful to the Department of Science and Technology (DST), Govt. of India, New Delhi for the award of a major research project (EMR/2016/007766) to him.
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