In this study, a series of Pr3+ ions doped Lithium Barium Tungstate (Li2Ba5W3O15) was synthesized using the conventional high-temperature solid state method. The structure and phase of the phosphors were analysed using X-ray diffraction (XRD) patterns. Fourier Transform Infrared (FT-IR) spectroscopy was used to examine the different vibrational bands present. The optical band gap values of the optimized LBW phosphor and the undoped LBW sample were measured using diffuse reflectance spectra (DRS). Under 319 nm excitation, the photoluminescence (PL) spectra of the Pr3+-activated LBW phosphor exhibited strong visible blue and reddish emissions at 488 nm and 647 nm respectively corresponding to the 3P0 → 3H4 and 3F2 transitions of the Pr3+ ions. The evaluated CIE color chromaticity coordinates of the as-prepared LBW:Pr3+ phosphors lie within the white region. The temperature-dependent PL (TDPL) measurement demonstrated relatively good thermal stability for the synthesized phosphor. Moreover, the fluorescence intensity ratio (FIR) was used to analyze the optical sensing properties of the LBW:Pr1.0 phosphor. A maximum relative sensitivity (Sr) of 1.03 % K−1indicated the potential of these phosphors for optical thermometry applications. A double exponential trend with decreasing lifetime was observed in the PL decay data at 647 nm emission (λem) under 319 nm excitation (λex), with an increase in the Pr3+ ions concentration in the host matrix. In conclusion, the investigations conducted demonstrate that the Pr3+ ions doped LBW phosphors show great potential for applications in solid-state lighting and optical thermometry. Its emission characteristics, thermal stability, and optical sensing capabilities establish it as a suitable candidate for these applications. 

Luminescence and optical thermometry strategy based on emission spectra of Li2Ba5W3O15:Pr3+ phosphors

Synthesis, Structural and Fluorescence Investigations of Novel Li2Ba5W3O15:Sm3+ Phosphors for Photonic Device Applications.

One of the interesting uses of phosphors is the development of non-contact thermometers apart from their usage as visible photonic devices. A series of Dy3+-doped Li2Ba5W3O15 (LBW) phosphors were successfully synthesized using high temperature solid-state reaction process. The crystal structure and morphology of LBW:xDy3+ phosphors were studied using X-ray diffraction (XRD), Rietveld refinements and field effect scanning electron microscopy (FE-SEM) with energy dispersive x-ray (EDX) analysis. The XRD and photoluminescence (PL) analyses validated the effective substitution of Ba2+ ions with Dy3+ ions. Two prominent emission peaks were found at 493 and 583 nm corresponding to 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions respectively under 368 nm excitation wavelength. A comprehensive analysis has been carried out on the usage of the Dy3+ doped LBW phosphors in fluorescence intensity ratio (FIR) thermometry. The optical temperature measurement performance of the LBW:xDy3+ phosphor was achieved by utilizing distinct thermal quenching transitions, specifically on 4F9/2→6H15/2,13/2, at temperatures ranging from 293 to 443 K. The as-prepared phosphors demonstrate excellent performance as optical thermometers, with a maximum relative sensitivity (Sr) of 0.7% K-1 at 293 K, an absolute sensitivity (Sa) of 4.68 K-1 at 443 K and a temperature resolution of ~0.51 at 443 K. These values indicate that the phosphors are highly responsive to changes in temperature, making them suitable for non-contact thermometry applications. 

Temperature sensing materials based on the Fluorescence Intensity Ratio in Li2Ba5W3O15:Dy3+ phosphors

A set of warm white phosphor samples Li2Ba5W3O15 (LBW):xDy3+, yEu3+ were prepared via high-temperature solid-state process. Field emission scanning electron microscopy (FE-SEM) and Energy-dispersive X-ray analysis (EDX) with X-ray diffraction (XRD) are the structural analyses that show the incorporation of Dy3+ and Eu3+ ions into the LBW host matrix, without causing any damage to the lattice structure. Fourier Transform Infrared Spectroscopy (FT-IR) approves the presence of distinct vibrational characteristics of the proposed phosphors. The band gaps of the prepared phosphor samples were determined using diffused reflectance spectral (DRS) data. The energy transfer between Dy3+ and Eu3+ ions was observed, contributing to the adjustable luminescence of the LBW:Dy3+/Eu3+ phosphors. By varying the activator doping levels while keeping the excitation wavelength constant, the emission colors of LBW:Dy3+/Eu3+ phosphors shift from natural white with negligible color purity to relatively pure orange-red region. The decay curves follow bi-exponential behavior of decreasing lifetime with increasing concentration of the activator ions. A temperature measurement model using fluorescence intensity ratio (FIR) was developed using D3E0.75 phosphor demonstrating excellent optical temperature measurement properties, with a maximum value of Sr (=0.97 % K−1). Therefore, all the experimental results indicate that the prepared Dy3+/Eu3+ co-doped LBW phosphors can be a suitable choice for UV excitable warm white lighting devices with color tunability and non-contact optical thermometry measurements. 

A single phase Li2Ba5W3O15:Dy3+/Eu3+ phosphor for color tunable devices and non-contact optical thermometry

Phosphate-based glasses are promising materials which are being employed for broad range of applications whereas Eu3+ is an efficient activator due to its predominant 5D0 →7F2 emission (red region). In this direction, an attempt has been made to investigate the effect of Eu3+ ions doped lead phosphate glasses (PPbKANEu: P2O5+PbO+K2O+Al2O3+Na2O+Eu2O3) to explore possible photonic device applications. Optical absorption, excitation, photoluminescence and decay rates are used to characterize the PPbKANEu glasses. The photoluminescence spectrum of Eu3+:PPbKAN glasses exhibit emission channels from the first excited (5D0) to the ground (7FJ (J =0–4)) multiplets. To determine the local site symmetry of surrounding Eu3+ ions, the relative fluorescence intensity ratio of 5D0→7F1 versus 5D0→7F2 emission channels has been analyzed. The emission spectrum of PPbKANEu glasses exhibits a comprehensive lifting of degeneracy of 5D0→7F2 and 5D0→7F1 emission channels. By considering C2v symmetry for Eu3+ ions, the second (B02= −406 and B22=−158) and fourth (B04=980, B24=297 and B44=926 cm–1) rank crystal–field (CF) characteristics were estimated along with CF strength factor (S= 402 cm–1). The lifetime of 5D0 state is estimated to be 2.09, 2.23, 2.21 and 2.21 ms for 0.1, 0.5, 1.0 and 2.0 mol% of Eu3+ ions, respectively. The analysis of the decay times reveals that the lifetime of 5D0 state is less affected by the concentration of the Eu3+ ion. The results are compared and discussed with reported values and confirm the potentiality of the PPbKANEu glasses for optical device applications in visible regions. 

Spectroscopic investigation and local structure of Eu3+ ions in lead phosphate glasses for optical device applications

A series of oxyfluoride strontium zinc borosilicate (OFSZBS) glasses co-doped with Dy3+/Eu3+ ions was prepared via melt quench method. The structural properties were examined using XRD and scanning electron microscope (SEM) with energy dispersive X-ray analysis (EDX) on DE2.0 and undoped OFSZBS glasses, respectively. UV–Vis absorption spectroscopy was used to evaluate the direct & indirect energy band gaps. At different excitations (348, 362, 385 and 393 nm), the photoluminescence (PL) spectra were observed with tuned light. Warm white light was generated through the Dy3+ (4F9/2→6H15/2, 6H13/2) and Eu3+ (5D0→7F2) transitions. Dexter Reisfield approximation applied to PL data revealed a dipole-dipole (d-d) mechanism accountable for the energy transfer (non-radiative) between sensitizer (Dy3+) and activator (Eu3+) ions. The energy transfer efficiency in the co-doped glass samples was found between 8% to 50%, depending on the doping. The Inokuti-Hirayama (I-H) fitting of PL decay profiles also confirm the energy transfer mechanism. The CIE chromaticity color coordinates observed for OFSZBSDE2.0 glass also confirm the color tunability. The above findings reveal the applications of as-prepared Dy3+/Eu3+ co-doped OFSZBS glasses excited using n-UV light for warm white LEDs and tuned devices. 

Efficient tunable photoluminescence of Dy3+/Eu3+ co-doped OFSZBS glasses for warm white LEDs

This paper investigates the synthesis and luminescence characteristics of Tm3+/Tb3+/Eu3+ co-doped Sr4Nb2O9 (SNB) phosphors as potential candidates for white light-emitting diodes (WLEDs). The study explores the energy transfer mechanisms and color-tunable characteristics of these phosphors. The SNB phosphors were prepared using a solid-state reaction method, and their structural and morphological properties were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier-transform infrared (FT-IR) spectroscopy. The diffuse reflectance, photoluminescence (PL) and time resolved photoluminescence (TRPL) properties were investigated, revealing efficient energy transfer processes from Tm3+ to Tb3+ and Eu3+ ions. The energy transfer mechanisms were determined through critical distance calculations and analysis of multipolar interactions. The co-doped phosphors exhibited tunable emission colors ranging from blue to white light, with controllable correlated color temperatures (CCTs) and high color rendering indices (CRIs). The CIE chromaticity coordinates were optimized to approach neutral white light. The PL intensity is maintained at 81.19% at 150 °C of that of room temperature which showcases the remarkable thermal stability of the as-prepared phosphors. The results highlight the potential of Tm3+/Tb3+/Eu3+ co-doped SNB phosphors for generating high-quality, color-tunable white light for advanced lighting applications.

Energy transfer mechanisms and color-tunable luminescence of Tm3+/Tb3+/Eu3+ co-doped Sr4Nb2O9 phosphors for high-quality white light-emitting diodes

The present study evaluated the adsorption of phosphate ions from an aqueous solution using rice
straw-based adsorbents. The batch study was performed to find the effect of pH, initial ion concentration,
a dose of adsorbent, contact time and temperature. The maximum adsorption capacity of raw and
modified rice straw is 6.47 mg/g and 16.60 mg/g. Both adsorbents (raw rice straw and modified rice
straw) showed good adsorption capacity at pH 8, adsorbent dose of 0.5 g for modified rice straw and
0.6 g for raw rice straw with an initial ion concentration of 20 ppm, contact time of 60 min at 100 rpm.
Adsorption isotherm, kinetics and thermodynamic studies were also performed for adsorption data.
The monolayer adsorption capacity was measured for raw rice straw at 6.21 mg/g and modified rice
straw at 6.36 mg/g. Freundlich isotherm (correlation coefficient 0.91 for raw rice straw and 0.96 for
modified rice straw) was best fitted to experimental data compared to Langmuir isotherm. The
pseudo-second-order showed a correlation coefficient of 0.99 for both adsorbents and was perfectly fit
to adsorption data. A thermodynamic adsorption study showed that the adsorption of phosphate ions
is endothermic and non-spontaneous at a lower temperature. The present study revealed that modified
rice straw adsorbent has good removal efficiency for phosphate ions.

Usability of Rice Straw as Biosorbent for the Removal of Phosphate from
Aqueous Solution: Isotherms, Kinetics and Thermodynamics

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Papers

Efficient tunable photoluminescence of Dy3+/Eu3+ co-doped OFSZBS glasses for warm white LEDs

Energy transfer mechanisms and color-tunable luminescence of Tm3+/Tb3+/Eu3+ co-doped Sr4Nb2O9 phosphors for high-quality white light-emitting diodes

Usability of Rice Straw as Biosorbent for the Removal of Phosphate from Aqueous Solution: Isotherms, Kinetics and Thermodynamics