[en] The present paper brings out the results concerning the preparation and optical properties of Sm³⁺ and Dy³⁺ each ion separately in four different concentrations (0.1, 0.5, 1.0 and 1.5 mol%) and also together doped (1 mol% Dy³⁺+x mol% Sm³⁺): Li₂O–LiF–B₂O₃–CdO (where x=0.1, 0.5, 1.0 and 1.5 mol%) glasses by a melt quenching method. Sm³⁺ doped base glasses have displayed an intense orange emission at 602 nm (⁴G_5/2→⁶H_7/2) with an excitation at 403 nm and Dy³⁺ doped glasses have shown two emissions located at 486 nm (⁴F_9/2→⁶H_15/2; blue) and 577 nm (⁴F_9/2→⁶H_13/2; yellow) with λ_exci=387 nm. The co-doped (Dy³⁺+Sm³⁺) lithium fluoro-boro cadmium glasses have been excited with an excitation at 387 nm of Dy³⁺ which has resulted in with a significant reduction in Dy³⁺ emission, at the same time there exists an increase in the reddish-orange emission of Sm³⁺ due to an energy transfer from Dy³⁺ to Sm³⁺. The non-radiative energy transfer from Dy³⁺ to Sm³⁺ is governed by dipole–quadrupole interactions as is explained in terms of their emission spectra, donor lifetime, energy level diagram and energy transfer characteristic factors. -- Highlights: • In co-doped (Dy³⁺+Sm³⁺): LFBCd glass, reddish-orange emission due to Sm³⁺ (⁴F_9/2→⁶H_J) has been enhanced due to an energy transfer from Dy³⁺ ions in the glass. • This has been evidenced from a lowering trend in the emission transition lifetimes of donor (Dy³⁺) ions with increasing acceptor (Sm³⁺) concentration. • Energy transfer mechanism involved in Dy³⁺→Sm³⁺ has been explained in terms of I–H luminescence decay curve analysis

[en] Graphical abstract: The energy transfer process occurring from Sm"3"+ to Eu"3"+ in B_2O_3–ZnO (BZn) glasses is analyzed. Based on the Foster–Dexter theory, the possibility of energy transfer between Sm"3"+ and Eu"3"+ has been demonstrated from the spectral overlap of Eu"3"+ absorption and Sm"3"+ emission, photoluminescence spectra, energy level diagram and lifetime measurements. The energy transfer mechanism in (Sm"3"+ + Eu"3"+) co-doped glass is governed by dipole–dipole interaction. - Highlights: • Spectroscopic properties of individually doped Sm"3"+, Eu"3"+ & co-doped (Sm"3"+ + Eu"3"+) in BZn glasses were studied separately. • The effect of Eu"3"+ concentration on luminescence properties is explained from cross-relaxations. • Energy transfer from Sm"3"+ ("4G_5_/_2) to Eu"3"+ ("5D_0) has been explained from Foster–Dexter theory. • Dipole–dipole mechanism governs the energy transfer from Sm"3"+ to Eu"3"+. - Abstract: The present paper reports on the results concerning to photoluminescence features of Eu"3"+, Sm"3"+ ions and energy transfer process occurring from Sm"3"+ to Eu"3"+ doped in 45 B_2O_3–55 ZnO (BZn) glasses prepared by melt quenching technique. Luminescence quenching as a function of Eu"3"+ concentration in BZn glasses has been discussed. Among the studied concentrations, 0.5 mol% of Eu"3"+ is optimized because it has exhibited red emission transition "5D_0 → "7F_2. With regard to Sm"3"+ glasses, orange emission at 602 nm ("4G_5_/_2 → "6H_7_/_2) has been noticed on exciting with λ_e_x_c_i = 403 nm. Based on the Foster–Dexter theory, the possibility of energy transfer between Sm"3"+ and Eu"3"+ has been explained from the spectral overlap of Eu"3"+ absorption and Sm"3"+ emission. The optimized concentration 0.5 mol% of Eu"3"+ is co-doped with Sm"3"+ in various concentrations ranging from 0.1 to 1.5 mol% inorder to study the sensitization effect of Sm"3"+ on Eu"3"+ luminescence. The results have revealed that with the addition of Sm"3"+ to Eu"3"+: BZn glass, emission intensity of Eu"3"+ has been enhanced due to migration of Sm"3"+ excitation energy. Energy transfer based enhanced emission in the co-doped (Sm"3"+ + Eu"3"+): BZn glasses have been discussed accordingly from photoluminescence spectra, energy level diagram and lifetime measurements, colour coordinates and also the mechanism governing the energy transfer process has been explained in detailed. Colour coordinates for the co-doped glasses upon exciting at 403 nm were also analysed. The results suggest that, the studied combination of rare earth ions could be promising candidates for red colour emitting LEDs in solid state lightning

[en] In the present paper, we report on the absorption and emission properties of (0.1-1.5 mol %) Ho³⁺ doped LFBCd (Li₂O₋LiF₋B₂O₃₋CdO) glasses prepared via melt quenching method. On exciting these glasses at (λ_exci) = 452 nm, two emissions at 556 nm (⁵S₂→⁵I₈; Green), 655 nm (⁵F₅→⁵I₈; Red) have been obtained. Upon exciting these glasses with a 980 nm diode laser, NIR emissions at 1195 nm (⁵I₆→⁵I₈), 1951 nm (⁵I₇→⁵I₈) have been measured for 1 mol % Ho³⁺:LFBCd glass. For higher concentration beyond 1.0 mol %, emission quenching of Ho³⁺ glass has been noticed and which has successfully been explained in terms of an energy level diagram. From absorption cross-section data, stimulated emission cross-section has been evaluated by applying McCumber's theory and further cross-sectional gain has also been computed for the emissions at 1195 nm (∼1.20 μm) and 1951 nm (∼2.0 μm) of 1 mol % Ho³⁺:LFBCd glass

[en] Highlights: • Single-phase LiMgBO₃:Tm³⁺/Dy³⁺ phosphors were synthesized by solid-state reaction method. • Quenching of Tm³⁺ emission and lifetime in the presence of Dy³⁺ demonstrates the ET from Tm³⁺→Dy³⁺ governed by dipole–dipole interaction. • The PL intensity of LiMgBO₃:Tm³⁺/Dy³⁺ exhibited nearly two-fold enhancement upon co-doping with 5% Li⁺ as a charge compensator. • The Color tunability from blue to white demonstrates the applicability of LiMgBO₃:Tm³⁺/Dy³⁺ as a white light phosphor in white LEDs. We report on thermal-, structural-, optical-, and energy transfer (ET)-based photoluminescence (PL) characteristics of Tm³⁺ co-doped with Dy³⁺ in a single-phase LiMgBO₃ host material. Tm³⁺ exhibits vibrant blue emission (¹D₂→³F₄: 456 nm) and Dy³⁺ displays strong yellowish-white emission (⁴F_9/2→⁶H_13/2: 573 nm) under ultraviolet (UV) excitation. When the optimum concentration (0.03) of Tm³⁺ is co-doped with different amounts of Dy³⁺, the PL intensity of Tm³⁺: ¹D₂→³F₄ declines but increases for Dy³⁺: ⁴F_9/2→⁶H_J (J = 11/2, 13/2, 15/2), which suggests ET from Tm³⁺→Dy³⁺ and demonstrates electric dipole–dipole interaction with a critical distance of 11.07 Å. The ET between Tm³⁺ and Dy³⁺ is validated from the spectral overlap of Tm³⁺ PL and Dy³⁺ absorption, Tm³⁺/Dy³⁺ PL spectra, Tm³⁺-dependent lifetimes, and ET parameters such as efficiency and probability. The Commission Internationale de l’Eclairage (CIE) coordinates display the color tunability of Tm³⁺ phosphor from blue light (0.146, 0.045) to warm white light (0.334, 0.306) with a correlated color temperature (CCT) value of 5,404 K in response to Dy³⁺ doping. The PL intensity of LiMgBO₃:0.03Tm³⁺/0.05Dy³⁺ increases nearly two-fold on co-doping with 5% Li⁺ as a charge compensator. Tm³⁺/Dy³⁺/Li⁺ co-activated material exhibits good thermal stability, retaining 64% of the initial PL intensity, which suggests its practical applicability as UV light triggered white light-emitting devices.

[en] Herein, we present energy transfer dependent photoemission properties of Dy³⁺ and Pr³⁺ ions co-doped in fluoro-borosilicate glasses. Dy³⁺ glasses exhibited emission at 483 nm and 577 nm under λ_exci = 387 nm; Pr³⁺ glasses displayed emission at 488 nm and 605 nm under λ_exci = 488 nm. The energy transfer (ET) process between Dy³⁺ and Pr³⁺ ions is investigated from the spectral overlap of absorption and emission of both ions and found that ET can occur from Pr³⁺ to Dy³⁺ (³P_1,0(Pr³⁺)+⁶H_15/2(Dy³⁺)→³H₄(Pr³⁺)+⁴F_9/2(Dy³⁺)) and from Dy³⁺ to Pr³⁺ (⁴F_9/2(Dy³⁺)+ ³H₄(Pr³⁺)→⁶H_15/2(Dy³⁺)+³P_1,0(Pr³⁺)). Further, by co-doping, the optimal content of Dy³⁺ (1.0 mol %) with different contents of Pr³⁺, PL spectra, the donor (Dy³⁺) dependent lifetimes, and ET parameters (η and P) are investigated and understood that the dipole-dipole interaction governs nonradiative ET from Dy³⁺ to Pr³⁺. These results demonstrate that the investigated glass systems can be potential candidates for employing in multicolor emitting devices under UV light.

[en] Mn⁴⁺-activated KGaP₂O₇ red emitting phosphor was successfully synthesized via traditional solid-state reaction method in air. The structural features of KGaP₂O₇:xMn⁴⁺ material were investigated by means of powder XRD & Raman, morphology from SEM, and element analysis, corresponding mapping through EDAX. In conjunction, concentration and temperature dependent spectroscopic properties were analyzed from UV–Vis reflectance, excitation, emission and lifetime decay curves. Powder XRD and photoluminescence profiles revealed that GaO₆ polyhedra offer Mn⁴⁺ ions to substitute the Ga³⁺ sites in the crystal lattice resulting in a pure single phase structure with an efficient red emission at 702 nm (Mn⁴⁺:²E_g→⁴A_2g) under 452 nm excitation. The emission decay curves exhibited non-exponential nature with lifetimes shortening when Mn⁴⁺ concentration is increased. Electric dipole-dipole interaction is identified to be responsible for the concentration quenching beyond 0.07 Mn⁴⁺ via energy transfer between Mn⁴⁺ ions. The temperature-dependent emission intensity for KGaP₂O₇:0.07Mn⁴⁺ exhibited 66% at 423 K (150 °C) displaying good thermal stability and activation energy (E_a) of ∼0.186 eV. From UV–Vis reflectance spectra using Tanabe-Sugano diagram, crystal splitting factor (Dq), two Racah parameters (B & C), Dq/B, C/B and energy of states are calculated to evaluate nephelauxetic ratio (β). In addition, the effect of Mn⁴⁺ content (concentration quenching) and temperature (thermal quenching) on emission intensity are discussed based on the Tanabe-Sugano energy diagram and configurational coordinate scheme of Mn⁴⁺. Therefore, KGaP₂O₇:Mn⁴⁺ phosphor can serve as a potential red emitting phosphor under blue light excitation and can also be useful to enhance plants growth.

[en] The present paper reports on the results pertaining to the emission properties of 0.5 mol% Er"3"+ and together (0.5 Yb"3"+ /0.5 Er"3"+) doped PZL (P_2O_5-ZnO-LiF) glasses prepared by a melt quenching method. From the optical absorption data, absorption and stimulated emission cross-sections have been evaluated using McCumber’s theory and further cross-sectional gain has also been computed for Yb"3"+/Er"3"+ doped glass. On exciting the single (Er"3"+) and dual rare earth ions (Yb"3"+/Er"3"+) doped glass sample at λ_e_x_c_i = 379 nm, three emission bands in the visible region "2H_1_1_/_2→"4I_1_5_/_2 (526 nm), "4S_3_/_2→"4I_1_5_/_2 (549 nm) and "4F_9_/_2→"4I_1_5_/_2 (664 nm) are observed and while at λ_e_x_c_i = 980 nm (Laser Diode) excitation a broad emission at 1530 nm attributed to "4H_1_3_/_2→"4I_1_5_/_2 is observed in the NIR region. The enhancement in visible and NIR emission intensities with the addition of Yb"3"+ to Er"3"+ due to an energy transfer process from Yb"3"+ to Er"3"+ has been explained in terms of an energy level diagram

[en] Highlights: • Petal-like 3D structured Ba₃(PO₄)₂:xSm³⁺+0.02Li⁺ phosphor with assembled nano spheres. • Refinement factor of Ba₃(PO₄)₂ are R_p = 10.91%, R_wp = 14.31%, R_exp = 11.07%, and GOF = 1.67. • The critical quenching concentration and distance of Sm³⁺ was 0.06 mol% and 22.2 Å. • CIE chromaticity coordinates is (0.5599,0.4368): dark yellow to orange emission. Highly uniform, petal-like, 3D-structured Ba₃(PO₄)₂ phosphors were fabricated by facile wet chemical aqueous solution route. The production mechanism of Ba₃(PO₄)₂ petal structure was optimized using XRD and SEM analysis grown under various temperatures and reaction times. Phase transition of Ba₃(PO₄)₂ from the hexagonal to rhombohedral occurred with increasing reaction temperature. The Rietveld refinement based XRD phase analysis demonstrated the successful formation of monophase Ba₃(PO₄)₂. Later, Ba₃(PO₄)₂ was doped with various amounts of Sm³⁺ ions and with charge balance by Li⁺ ions. Ba₃(PO₄)₂: Sm³⁺+Li⁺ samples at 0.06 mol of Sm³⁺ concentration displayed maximum luminescence intensity in response to 402 nm excitation. Increasing the Sm³⁺ content over the 0.06 mol, emission quenching behavior was observed and it was explained by Dexter’s theory. The chromaticity coordinates of the Ba₃(PO₄)₂:Sm³⁺+Li⁺ phosphor material were calculated to be (0.5558, 0.4380), suggesting that it will be a potential yellow phosphor for use in W-LEDs in combination with blue LEDs chips.