Optical,emission, and excitation dynamics of Eu3+-doped bismuth-based phosphate glass for visible display laser applications

Eu³⁺-doped-bismuth-based phosphate glasses with chemical equation (60 − x)P₂O₅–20Bi₂O₃−10Na₂CO₃–10SrF₂–xEu₂O₃ (PBNSEu), (where x = 0, 0.1, 0.5, 1.0, 1.5 and 2 mol%) were fabricated using the melt-quenching method. Obtain X-ray diffraction (XRD), energy-dispersive X-ray (EDAX), and Fourier transform infrared (FTIR) spectra were used to characterize the structure of the prepared PBNSEu glass. The J–O (Judd–Ofelt) intensity parameters (Ω₂, Ω₄) were estimated using photoluminescence emission spectra. When excited with a xenon lamp at λ_exc = 394 nm, the most intense red-emission transition occurred at ~612 nm (⁵D₀→⁷F₂). J–O intensity parameters were used to calculate radiative properties, whereas the radiative branching ratio (β_R), radiative transition probability (A_R), radiative lifetime (τ_R), and total radiative transition rate (A_τ) were calculated for the transitions ⁵D₀→⁷F_J (where J = 0–4) and were obtained in the emission spectra for europium ion-doped in the current glass. Using the CIE1931 chromaticity coordinates axes, the colours of various concentrations of Eu³⁺ ion-doped PBNS glass were evaluated using the emission spectra. Temperature-dependent luminescence spectra were recorded for the optimized PBNSEu20 glass to calculate the activation energy. These results strongly suggested red components in w-LEDs and visible display laser applications.     

Concentration‐dependent studies of Nd3+‐doped zinc phosphate glasses for NIR photoluminescence at 1.05 μm

Nd³⁺‐doped lead‐free zinc phosphate glasses with the chemical compositions (60‐x) NH₄H₂PO₄ + 20ZnO + 10BaF₂ + 10NaF + xNd₂O₃ (where x = 0.5, 1.0, 1.5, 2.0 and 2.5 mol%) were prepared using a melt quenching technique. Vibrational bands were assigned and clearly elucidated by Raman spectral profiles for all the glass samples. Judd–Ofelt (J–O) intensity parameters (Ω_λ: λ = 2, 4, 6) were obtained from the spectral intensities of different absorption bands of Nd³⁺ ions. Radiative properties such as radiative transition probabilities (A_R), radiative lifetimes (τ_R) and branching ratios (β_R) for different excited states were calculated using J–O parameters. The near infrared (NIR) photoluminescence spectra exhibited three emission bands (⁴F_3/2 level to ⁴I_13/2, ⁴I_11/2 and ⁴I_9/2 states) for all the concentrations of Nd³⁺ ions. Various luminescence properties were studied by varying the Nd³⁺ concentration for the three spectral profiles. Fluorescence decay curves of the ⁴F_3/2 level were recorded. The energy transfer mechanism that leads to quenching of the ⁴F_3/2 state lifetimes was discussed at higher concentration of Nd³⁺ ions. These glasses are suggested as suitable hosts to produce efficient lasing action in NIR region at 1.05 μm.     

Optical analysis of RE3+ (RE = Pr3+, Er3+ and Nd3+):cadmium lead boro tellurite glasses

This article reports on the optical characterization of Pr³⁺‐, Er³⁺‐ and Nd³⁺‐doped cadmium lead boro tellurite (CLBT) glasses prepared using the melt quenching method. The visible–near infrared (Vis–NIR) absorption spectra of these glasses were analyzed systematically. On measuring the NIR emission spectra of Er³⁺:CLBT glasses, a broad emission band centered at 1536 nm (⁴I_13/2 → ⁴I_15/2) was observed, as were three NIR emission bands at 900 nm (⁴F_3/2 → ⁴I_9/2), 1069 nm (⁴F_3/2 → ⁴I_11/2) and 1338 nm (⁴F_3/2 → ⁴I_13/2) from Nd³⁺:CLBT glasses and an NIR emission band at 1334 nm (¹G₄ → ³H₅) from Pr³⁺:CLBT glasses at an excitation wavelength (λ_ex) of 514.5 nm (Ar⁺ laser). Copyright © 2016 John Wiley & Sons, Ltd.     

Spectral investigations on Eu3+,Sm3+‐doped and Sm3+/Eu3+ co‐doped potassium‐fluoro‐phosphate glass emitting intense orange‐red for lighting applications

Potassium fluoro‐phosphate (KFP) glass singly doped with different concentrations of europium (Eu³⁺) or samarium (Sm³⁺) or co‐doped (Sm³⁺/Eu³⁺) was prepared, and their luminescence spectra were investigated. The phase composition of the product was verified by X‐ray diffraction analysis. Optical transition properties of Eu³⁺ in the studied potassium phosphate glass were evaluated in the framework of the Judd–Ofelt theory. The radiative transition rates (A_R), fluorescence branching ratios (β), stimulated emission cross‐sections (σ_e) and lifetimes (τ_exp) for certain transitions or levels were evaluated. Red emission of Eu³⁺ was exhibited mainly by the ⁵D₀→⁷F₂ transition located at 612 nm. Concentration quenching and energy transfer were observed from fluorescence spectra and decay curves, respectively. It was found that the lifetimes of the ⁵D₀ level increased with increase in concentration and then decreased. By co‐doping with Sm³⁺, energy transfer from Sm³⁺ to Eu³⁺ occurred and contributed to the enhancement in emission intensity. Intense orange‐red light emission was obtained upon sensitizing with Sm³⁺ in KFP glass. This approach shows significant promise for use in reddish‐orange lighting applications. The optimized properties of the Sm³⁺/Eu³⁺ co‐doped potassium phosphate glass might be promising for optical materials.     

Lasing transition at 1.06 μm emission in Nd3+‐doped borate‐based tellurium calcium zinc niobium oxide glasses for high‐power solid‐state lasers

The spectroscopic properties of Tellurium Calcium Zinc Niobium oxide Borate (TCZNB) glasses of composition (in mol%) 10TeO₂ + 15CaO + 5ZnO + 10 Nb₂O₅ + (60 – x)B₂O₃ + Nd₂O₃ (x = 0.1, 0.5, 1.0 or 1.5 mol%) have been investigated experimentally. The three phenomenological intensity parameters Ω₂, Ω_4, Ω₆ have been calculated using the Judd–Ofelt theory and in turn radiative properties such as radiative transition probabilities, emission cross‐sections, branching ratios and radiative lifetimes have been estimated. The trend found in the JO intensity parameter is Ω₂ > Ω₆ > Ω₄ If Ω₆ > Ω₄, the glass system is favourable for the laser emission ⁴F_3/2 → ⁴I_11/2 in the infrared (IR) wavelength. The experimental values of branching ratio of ⁴F_3/2 → ⁴I_11/2 transition indicate favourable lasing action with low threshold power. The evaluated total radiative transition probabilities (A_T), stimulated emission cross‐section (σ_e) and gain bandwidth parameters (σ_e × Δλ_p) were compared with earlier reports. An energy level analysis has been carried out considering the experimental energy positions of the absorption and emission bands.     

Study of trivalent samarium ion embedded lithium‐based borate glass for high‐density optical memory devices

Sm³⁺ ions doped strontium lithium lead borate glasses (SLLB:Sm) were prepared using a conventional melt‐quenching technique. The glasses were analyzed using X‐ray diffractometry and Fourier transform infrared spectroscopy, optical absorption, fluorescence spectral analysis, and fluorescence lifetime decay. The Judd–Ofelt (J–O) parameters and radiative parameters of the SLLB:Sm10 glass (1.0 mol% Sm³⁺ ion‐doped glass) were calculated using J–O theory. From the emission spectra, among all the synthesized glass, SLLB:Sm10 glass had the highest emission intensity for ⁴G_5/2→⁶H_11/2 transition (610 nm). Emission parameters, such as stimulated emission cross‐section and optical gain bandwidth, were calculated. For all concentrations of Sm³⁺ ions, the decay profile showed an exponential nature and decreased when the Sm³⁺ ion concentration was increased due to a concentration quenching effect. This result suggests that the synthesized SLLB:Sm10 glass could be used for application in high‐density optical memory devices.     

Optical analysis of RE3+ (RE = Nd or Er):B2O3–P2O5–CaF2–ZnO–(Li2O/Na2O/K2O) glasses

Calcium boro fluoro zinc phosphate glasses modified using alkali oxide and doped with Nd³⁺ and Er³⁺ ions with the chemical composition of 69.5 (B₂O₃) + 10 (P₂O₅) + 10 (CaF₂) + 5 (ZnO) + 5 (Na₂O/Li₂O/K₂O) + 0.5 (Er₂O₃/Nd₂O₃) were prepared using a conventional melt quenching technique. The results of X-ray diffraction patterns indicated the amorphous nature of all the prepared glasses. The visible–near-infrared red (NIR) absorption spectra of these glasses were analyzed systematically. The NIR emission spectra of Er³⁺ and Nd³⁺:calcium boro fluoro zinc phosphate glasses showed prominent emission bands at 1536 nm (⁴I_13/2→⁴I_15/2) and 1069 nm (⁴F_3/2→⁴I_11/2) respectively with λ_exci = 514.5 nm (Ar⁺ laser) as the excitation source.     

Photoluminescence properties of aeschynite‐type LaNbTiO6:RE3+ (RE = Tb,Dy, Ho) down‐converting phosphors

In this study, a series of LaNbTiO₆:RE³⁺ (RE = Tb, Dy, Ho) down‐converting phosphors were synthesized using a modified sol–gel combustion method, and their photoluminescence (PL) properties were investigated as a function of activator concentration and annealing temperature. The resultant particles were characterized using X‐ray diffraction, transmission electron microscopy, scanning electron microscopy, UV/Vis diffuse reflectance spectroscopy and PL spectra. The highly crystalline LaNbTiO₆:RE³⁺ (RE = Tb, Dy, Ho) phosphors with an average size of 200–300 nm obtained at 1100°C have an orthorhombic aeschynite‐type structure and exhibit the highest luminescent intensity in our study range. The emission spectra of LaNbTiO₆:RE³⁺ (RE = Tb, Dy, Ho) phosphors under excitations at UV/blue sources are mainly composed of characteristic peaks arising from the f–f transitions of RE³⁺, including 489 nm (⁵D₄ → ⁷F₆) and 545 nm (⁵D₄ → ⁷F₅) for Tb³⁺, 476 and 482 nm (⁴F_9/2 → ⁶H_15/2) and 571 nm (⁴F_9/2 → ⁶H_13/2) for Dy³⁺, and 545 nm (⁵F₄ + ⁵S₂ → ⁵I₈) for Ho³⁺, respectively. The luminescent mechanisms were further investigated. It can be expected that these phosphors are of intense interest and potential importance for many optical applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Luminescence properties of a novel red phosphor 6LaPO4–3La3PO7–2La7P3O18:Eu3+

Eu³⁺‐doped 6LaPO₄–3La₃PO₇–2La₇P₃O₁₈ red luminescent phosphors were synthesized by co‐deposition and high‐temperature solid‐state methods and its polyphase state was confirmed by X‐ray diffraction analysis. Transmission electron microscopy showed the grain morphology as a mixture of rods and spheres. Luminescence properties of the phosphor were investigated and its red emission parameters were evaluated as a function of Eu³⁺ concentration (3.00–6.00 mol%). Excitation spectra of 6LaPO₄–3La₃PO₇–2La₇P₃O₁₈:Eu³⁺ showed strong absorption bands at 280, 395, and 466 nm, while the luminescence spectra exhibited prominent red emission peak centred at 615 nm (⁵D₀→⁷F₂) in the red region. CIE chromaticity coordinates of the 6LaPO₄–3La₃PO₇–2La₇P₃O₁₈:5%Eu³⁺ phosphor were (0.668, 0.313) in the red region, and defined its potential application as a red phosphor.     

Emission analysis of RE3+ (RE = Sm,Dy):B2O3‐TeO2‐Li2O‐AlF3 glasses

This article reports on the optical properties of 0.5% mol of Sm³⁺, Dy³⁺ ion‐doped B₂O₃‐TeO₂‐Li₂O‐AlF₃ (LiAlFBT) glasses. The glass samples were characterized by optical absorption and emission spectra. Judd‐Ofelt theory was applied to analyze the optical absorption spectra and calculate the intensity parameters and radiative properties of the emission transitions. The emission spectra of Sm³⁺ and Dy³⁺:LiAlFBT glasses showed a bright reddish‐orange emission at 598 nm (⁴G_5/2 → ⁶H_7/2) and an intense yellow emission at 574 nm (⁴F_9/2 → ⁶H_13/2), respectively. Full width at half maximum (FWHM), stimulated emission cross section, gain bandwidth and optical gain values were also calculated to extend the applications of the Sm³⁺ and Dy³⁺:LiAlFBT glasses. Copyright © 2012 John Wiley & Sons, Ltd.     

Improving green emission of Tb3+ ions in BaO‐B2O3‐P2O5 glasses by means of Al3+ ions

BaO‐B₂O₃‐P₂O₅ glasses doped with a fixed concentration of Tb³⁺ ions and varying concentrations of Al₂O₃ were synthesized, and the influence of the Al³⁺ ion concentration on the luminescence efficiency of the green emission of Tb³⁺ ions was investigated. The optical absorption, excitation, luminescence spectra and fluorescence decay curves of these glasses were recorded at ambient temperature. The emission spectra of terbium ions when excited at 393 nm exhibited two main groups of bands, corresponding to ⁵D₃ → ⁷F_j (blue region) and ⁵D₄ → 7F_j (green region). From these spectra, the radiative parameters, viz., spontaneous emission probability A, total emission probability A_T, radiative lifetime τ and fluorescent branching ratio β, of different transitions originating from the ⁵D₄ level of Tb³⁺ ions were evaluated based on the Judd‐Ofelt theory. A clear increase in the quantum efficiency and luminescence of the green emission of Tb³⁺ ions corresponding to ⁵D₄ → ⁷F₅ transition is observed with increases in the concentration of Al₂O₃ up to 3.0 mol%. The improvement in emission is attributed to the de‐clustering of terbium ions by Al³⁺ ions and also to the possible admixing of wave functions of opposite parities. Copyright © 2016 John Wiley & Sons, Ltd.     

Emission analysis of Tb3+‐and Sm3+‐ion‐doped (Li2O/Na2O/K2O) and (Li2O + Na2O/Li2O + K2O/K2O + Na2O)‐modified borosilicate glasses

Four series of borosilicate glasses modified by alkali oxides and doped with Tb³⁺ and Sm³⁺ ions were prepared using the conventional melt quenching technique, with the chemical composition 74.5B₂O₃ + 10SiO₂ + 5MgO + R + 0.5(Tb₂O₃/Sm₂O₃) [where R = 10(Li₂O /Na₂O/K₂O) for series A and C, and R = 5(Li₂O + Na₂O/Li₂O + K₂O/K₂O + Na₂O) for series B and D]. The X‐ray diffraction (XRD) patterns of all the prepared glasses indicate their amorphous nature. The spectroscopic properties of the prepared glasses were studied by optical absorption analysis, photoluminescence excitation (PLE) and photoluminescence (PL) analysis. A green emission corresponding to the ⁵D₄ → ⁷F₅ (543 nm) transition of the Tb³⁺ ions was registered under excitation at 379 nm for series A and B glasses. The emission spectra of the Sm³⁺ ions with the series C and D glasses showed strong reddish‐orange emission at 600 nm (⁴G_5/2 →⁶H_7/2) with an excitation wavelength λ_exci = 404 nm (⁶H_5/2→⁴F_7/2). Furthermore, the change in the luminescence intensity with the addition of an alkali oxide and combinations of these alkali oxides to borosilicate glasses doped with Tb³⁺ and Sm³⁺ ions was studied to optimize the potential alkali‐oxide‐modified borosilicate glass.     

Preparation and luminescence properties of KLaSiO4:Tb3+ phosphors

KLaSiO₄:Tb³⁺ phosphors were synthesized using the sol–gel method. The structure and luminescence properties of the materials were characterized using X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, thermogravimetry–differential thermal analysis, fluorescence spectra and calculated Commission Internationale de l'éclairage coordinates. The results showed that the material had a hexagonal structure, and that doping of Tb³⁺ did not change the crystal structure of KLaSiO₄. FTIR spectroscopy confirmed the existence of stretching vibrations of Si–O, bending vibrations of Si–O–Si, and asymmetric tensile vibrations of Si–O in KLaSiO₄. The excitation spectrum of the sample consisted of 4f⁷→5d¹ broadband absorption and the characteristic excitation peak of Tb³⁺, the excitation peak at 232 nm belongs to the spin allowed ⁷F_J→⁷D_J transition of Tb³⁺, the excitation peak at 268 nm belongs to the spin forbidden ⁷F_J→⁹D_J transition of Tb³⁺, and the absorption band of ⁷F_J→⁷D_J transition is split. Under excitation at 232 nm, the emission peak of the sample was composed of the ⁵D₄→⁷F_J (J = 6, 5, 4, 3) energy level transition of Tb³⁺. The highest emission peak is located at 543 nm, which belongs to the ⁵D₄→⁷F₅ transition and emits green light. Concentration quenching occurred when the Tb³⁺ doping concentration was greater than 1% mol, the quenching mechanism was an electric dipole–electric dipole action. When the ratio of citric acid to total metal ions was 1:1 and the annealing temperature was 800°C, the surface defects of the phosphors were greatly reduced, the quenching effect was reduced, and the luminous intensity reached the maximum.     

Europium‐activated rare earth fluoride (LnF3:Eu3+–Ln = La,Gd) nanocrystals prepared by using ionic liquid/NH4F as a fluorine source via hydrothermal synthesis

Lanthanide (Ln) fluorides are considered exceptional luminescent rigid host matrices for various optical active Ln³⁺ ions due to their high refractive index, high chemical stability and low phonon energy, leading to the low probability of non‐radiative decay, which results in higher photoluminescence quantum yield (PLQY) (usually higher than oxide hosts). In this study, Eu³⁺‐activated Ln fluorides (LnF₃:Eu³⁺–Ln = La, Gd) are synthesized by the hydrothermal method using 1‐butyl‐3‐methylimidazolium tertrafluoroborate [BMIBF₄] and NH₄F as fluorine precursors. The synthesized nanocrystals (NCs) are structurally and morphologically characterized, and their optical properties investigated using spectrofluorometry. The X‐ray diffraction (XRD) patterns of Eu³⁺‐substituted and ‐unsubstituted LnF₃ (prepared from a different fluorine source) are indexed based on the hexagonal and orthorhombic crystal structure, respectively. Average crystalline sizes are calculated using the Scherrer equation and it is found that the synthesized NCs have an average crystalline size of 12–35 nm. Transmission electron microscopy (TEM) images reveal that the NCs are well dispersed and nearly ellipsoid, with an average size of ~ 5 nm. Eu³⁺‐activated NCs show characteristic excitation and emission spectra. The emission spectra show both magnetic (⁵D₀–⁷F₁) and electric (⁵D₀–⁷F₂) dipole transition with appropriate CIE color coordinates; however, the intensity of the magnetic dipole transition is high, which is in accordance with local site symmetry. Owing to their unique size and excellent optical properties, the synthesized NCs may have potential application in the fields bio‐imaging and solar concentrators. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and photoluminescence properties of Eu3+‐activated Ba2Mg(PO4)2 phosphor

In this paper, we have reported the photoluminescence (PL) properties of the Ba₂Mg(PO₄)₂:Eu³⁺ phosphor synthesized using a wet chemical method. The preliminary scanning electron microscopy (SEM) investigation of the sample revealed irregular surface morphology with particle sizes in the 10–50 μm range. The strongest PL excitation peak was observed at 396 nm. The emission spectra indicated that this phosphor can be effectively excited by the 396 nm wavelength. Upon 396 nm excitation, the emission spectrum showed characteristics peaks located at 592 nm and 615 nm. These intense orange‐red emission peaks were obtained due to f→f transitions of Eu³⁺ ions. The emission peak at 592 nm is referred to as the magnetic dipole ⁵D₀→⁷F₁ transition and the emission peak at 615 nm corresponded to the electric dipole ⁵D₀→⁷F₂ transition of Eu³⁺. The Commission Internationale de l’Eclairage (CIE) coordinates of the Ba₂Mg(PO₄)₂:Eu³⁺ phosphor were found to be (0.586, 0.412) for wavelength 592 nm and (0.680, 0.319) for wavelength 615 nm situated at the edge of the CIE diagram, indicating high colour purity of phosphors. Due to the high emission intensity and a good excitation profile, Eu³⁺‐doped Ba₂Mg(PO₄)₂ phosphor may be a promising orange‐red phosphor candidate for solid‐state lighting applications.     

Synthesis and luminescence properties of Ca3Ga2Si3O12:RE3+ (RE = Eu/Tb) powder phosphors

Rare earth ions (Eu³⁺ or Tb³⁺)‐activated Ca₃ Ga₂ Si₃O₁₂ (CaGaSi) phosphors were synthesized by using a sol–gel method. Photoluminescence spectra of Eu³⁺:CaGaSi phosphors exhibited five emission bands at 578, 592, 612, 652 and 701 nm, which were assigned to the transitions (⁵D₀ → ⁷F₀, ⁷F_1, ⁷F₂, ⁷F₃ and ⁷F₄), respectively, with an excitation wavelength of λ_exci = 392 nm. Among these, the transition ⁵D₀ → ⁷F₂ (612 nm) displayed bright red emission. In the case of Tb³⁺:CaGaSi phosphors, four emission bands were observed at 488 (⁵D₄ → ⁷F₆), 543 (⁵D₄ → ⁷F₅), 584 (⁵D₄ → ⁷F₄) and 614 nm (⁵D₄ → ⁷F₃) from the measurement of PL spectra with λ_exci = 376 nm. Among these, the transition ⁵D₄ → ⁷F₅ at 543 nm displayed bright green emission. The structure and morphology of the phosphors were studied from the measurements of X‐ray diffraction (XRD), scanning electron microscopy (SEM) and energy‐dispersive X‐ray analysis (EDAX) results. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis of the structure and luminescence properties of Zn2GeO4:Eu3+ according to Judd–Ofelt theory

The preparation and characteristic of nanorod-like Zn₂GeO₄ doped with Eu³⁺ or zinc germanate (ZGO):xEu³⁺ (x = 0 ÷ 0.05), which was synthesized using the hydrothermal method, are described. The influence of Eu³⁺-doping ions on the structure and the optical properties of ZGO was also investigated. According to the photoluminescence spectra, ZGO:xEu³⁺ nanophosphors gave a red emission due to the ⁵D₀→⁷F₂ emission of Eu³⁺ ions. In accordance with Judd–Ofelt theory, the intensity parameters for f–f transitions from the emission and absorption spectrum were determined. At the ⁵D₀ excited state of Eu³⁺, total spontaneous emission probabilities (A_R), lifetimes (τ_R), branching ratios (β_R), and quantum efficiency (η) were calculated. The ZGO:xEu³⁺ (x = 0.02, 0.03, 0.04) phosphor showed the branch ratio β (⁵D₀→⁷F₂) > 60%, indicating that the phosphors prepared here have a promising potential as laser light. The sample with a concentration of 0.04Eu³⁺ achieved the highest quantum efficiency of 84%, suggesting that it has potential light-emitting diode applications.     

Optical analysis of RE3+ (RE = Eu,Tb):MgLa2V2O9 nano-phosphors

Red and green rare-earth ion (RE³⁺) (RE = Eu, Tb):MgLa₂V₂O₉ micro-powder phosphors were produced utilizing a standard solid-state chemical process. The X-ray diffraction examination performed on the phosphors showed that they were crystalline and had a monoclinic structure. The particles grouped together, as shown in the scanning electron microscopy (SEM) images. Powder phosphors were examined using a variety of spectroscopic techniques, including photoluminescence (PL), Fourier-transform infrared, and energy dispersive X-ray spectroscopy. Brilliant red emission at 615 nm (⁵D₀ → ⁷F₂) having an excitation wavelength (λ_exci) of 396 nm (⁷F₀ → ⁵L₆) and green emission at 545 nm (⁵D₄ → ⁷F₅) having an λ_exci = 316 nm (⁵D₄ → ⁷F₂) have both been seen in the emission spectra of Tb³⁺:MgLa₂V₂O₉ nano-phosphors. The emission mechanism that is raised in Eu³⁺:MgLa₂V₂O₉ and Tb³⁺:MgLa₂V₂O₉ powder phosphors has been explained in an energy level diagram.     

Luminescence properties of neodymium,samarium, and europium niobate and tantalate thin films

Thin films of lanthanide orthoniobate LnNbO₄ (LnNO) and orthotantalate LnTaO₄ (LnTO), (Ln = Nd, Sm, Eu) were fabricated using the sol–gel method with subsequent spin-coating on the PbZrO₃/Al₂O₃ substrate and annealing at 1000°C. X-ray diffraction patterns showed monoclinic M-LnNbO₄ or M´-LnTaO₄, which coexists with the orthorhombic or tetragonal phase. X-ray photoelectron spectroscopy demonstrated the presence of Nd³⁺, Sm³⁺/Sm²⁺ and Eu³⁺/Eu²⁺ ions. The luminescence properties of polymorphic films were investigated. Excitation spectra of PbZrO₃ interlayer represented broad bands at 410 and 550 nm that were assigned to charge transfer bands (CTB). In all films, the CTB broad band at ~275 nm related to charge transfer transition of Ln³⁺→O²⁻ and NbO₄³⁻ or TaO₄³⁻ groups. In excitation spectra, ⁴I_9/2→⁴G_5/2 (Nd³⁺), ⁶H_5/2→⁶P_3/2 (Sm³⁺) and ⁷F₀→⁵L₆ (Eu³⁺) transitions (at 585, 402 and 395 nm), respectively were found to be more intense than any other Ln³⁺ transition. The emission spectra showed narrow and intense bands at 1065, 600, and 614 nm that were ascribed to Nd³⁺, Sm³⁺, and Eu³⁺ 4f–f intraconfigurational transitions ⁴F_3/2→⁴I_11/2, ⁴G_5/2→⁶H_7/2, and ⁵D₀→⁷F₂, respectively. The excellent luminescence properties of films make them new potential groups for visible and/or near-infrared applications such as sensors and imaging equipment.     

Upconverted photoluminescence in Ho3+ and Yb3+ codoped Gd2O3 nanocrystals with and without Li+ ions

The upconversion photoluminescence of Ho³⁺ ion sensitized by Yb³⁺ ion in Ho³⁺/Yb³⁺codoped Gd₂O₃ nanocrystals with and without Li⁺ is investigated in this paper. Strong fluorescence in the green (534–570 nm) and red (635–674 nm) regions of the spectrum has been observed, arising from the ⁵F₄/⁵S₂ → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions of Ho³⁺ ion, respectively. Yb³⁺ ion is considered to be a better sensitizer for catching enough pumping energy and transferring considerable energy to Ho³⁺ in the Ho³⁺/Yb³⁺system. The upconversion intensity emitted by Ho³⁺ is greatly enhanced when Li⁺ is added to the Ho³⁺/Yb³⁺ codoped Gd₂O₃ nanocrystals.