Photoluminescence, γ-irradiation and X-ray induced luminescence studies of Sm3+-doped oxyfluorosilicate glasses and glass-ceramics

Sm³⁺-doped oxyfluorosilicate glasses were fabricated through traditional melt quenching technique. After the heat treatment of the prepared glass, transparent SrF₂ nanocrystalline glass-ceramics (GC) were obtained. The amorphous nature of the prepared glasses and crystalline phase (SrF₂) of the GC were confirmed by XRD analysis. Abbe number was calculated for all the prepared glasses by measuring refractive index at different wavelengths. In the framework of Judd-Ofelt (JO) theory, the JO intensity parameters were obtained from the absorption spectra of 1.0 mol% Sm₂O₃-doped glass. The photoluminescence spectrum was recorded with 401 nm excitation. From the analysis of optical spectra and JO parameters, the radiative properties like radiative transition probabilities, branching ratios and radiative lifetimes for the fluorescent levels of Sm³⁺ ions were determined. The effect of γ-irradiation on luminescence properties and X-ray induced luminescence properties were also studied. The emission intensity was increased for GC where as it decreases with increase of γ-irradiation dosages. There are no noticeable changes in the position as well as intensity in photoluminescence and X-ray induced luminescence spectra for GC sample but after the γ-irradiation, the emission intensity was decreased moderately. The luminescence decay profiles for ⁴G_5/2 level were recorded and it is changed from exponential to non-exponential nature for higher Sm³⁺ ion concentrations. The decay profiles which exhibit non-exponential nature are well fitted to the Inokuti-Hirayama model and determined the energy transfer parameters. By using the integrating sphere, the quantum yield values were obtained for all the prepared glasses. The detailed study of the present glasses reveals that these glasses could be useful for radiation shielding and scintillation applications.     

Synthesis and luminescence properties of novel Y2Si4N6C:Sm3+ carbonitride phosphor

Novel Y₂Si₄N₆C:Sm³⁺ phosphors for white light-emitting diodes (w-LEDs) were prepared by a carbothermal reduction and nitridation method. X-ray diffraction (XRD) and photoluminescence spectra were utilized to characterize the structure and luminescence properties of the as-synthesized phosphors. The emission spectrum obtained by excitation into 291 nm contains exclusively the characteristic emission of Sm³⁺ at 568, 607 and 654 nm which correspond to the transitions from ⁴G_5/2 to ⁶H_5/2, ⁶H_7/2, and ⁶H_9/2 of Sm³⁺, respectively. The strongest one is located at 607 nm due to ⁴G_5/2–⁶H_7/2 transition of Sm³⁺. It was found that concentration quenching occurred as a result of dipole–dipole interaction according to Dexter's theory. The temperature dependence of photoluminescence properties was investigated from 25 to 300 °C and the prepared Y₂Si₄N₆C:Sm³⁺ phosphors showed superior thermal quenching properties.     

Photoluminescence properties of a double perovskite tungstate based red-emitting phosphor NaLaMgWO6:Sm3+

In this work, the conventional solid-state method was applied to synthesize a series of red-emitting NaLaMgWO₆:Sm³⁺ phosphors. The crystal structure, phase purity, morphology, particle size distribution as well as elemental composition of the as-prepared phosphors were investigated carefully with the aid of XRD, SEM, EDS, FT-IR analyses, indicating the high-purity and micron-sized NaLaMgWO₆:Sm³⁺ phosphors with monoclinic structure were prepared successfully. The spectroscopic properties of Sm³⁺ in NaLaMgWO₆ host including UV–vis diffuse reflection spectrum, photoluminescence excitation and emission spectra, decay curves, chromaticity coordinates and internal quantum efficiency were investigated in detail. Upon excitation with UV (290 nm) and n-UV (406 nm), NaLaMgWO₆:Sm³⁺ phosphor presented red emission corresponding to the ⁴G_5/2→⁶H_J (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm³⁺, in which the hypersensitive electronic dipole transition ⁴G_5/2→⁶H_9/2 (645 nm) was with the strongest emission intensity because Sm³⁺ ions were located at a lattice site with anti-inversion symmetry. The optimal concentration of Sm³⁺ was different for the given excitation wavelength such as 290 nm and 406 nm, which was interpreted by the extra effect of the energy transfer from W⁶⁺-O^2- group to Sm³⁺. The decay lifetime for ⁴G_5/2→⁶H_9/2 transition of Sm³⁺ was very short (< 1 ms) and decreased with the increasing Sm³⁺ concentration. The present investigation indicates that NaLaMgWO₆:Sm³⁺ phosphor could be a potential red component for application in w-LEDs.     

Red-emitting enhancement of Bi4Si3O12:Sm3+ phosphor by Pr3+ co-doping for White LEDs application

In this account, Bi₄Si₃O₁₂:Sm³⁺ and (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) red phosphors were prepared by solution combustion method fueled by citric acid at 900 °C for 1 h. The effects of co-doping Pr³⁺ ions on red emission properties of Bi₄Si₃O₁₂:Sm³⁺ phosphors, as well as the mechanism of interaction between Sm³⁺ and Pr³⁺ ions were investigated by various methods. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) revealed that smaller amounts of doped rare earth ions did not change the crystal structure and particle morphology of the phosphors. The photoluminescence spectroscopy (PL) indicated that shape and position of the emission peaks of (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors excited at λ_ex=403 nm were similar to those of Bi₄Si₃O₁₂:Sm³⁺ phosphors. The strongest emission peak was recorded at 607 nm, which was attributed to the ⁴G_5/2→⁶H_7/2 transition of the Sm³⁺ ion. The photoluminescence intensities of Bi₄Si₃O₁₂:Sm³⁺ phosphors were significantly improved by co-doping with Pr³⁺ ions and were maximized at Sm³⁺ and Pr³⁺ ions doping concentrations of 4 mol% and 0.1 mol%, respectively. The characteristic peaks of Sm³⁺ ions were displayed in the emission spectra of (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors excited at respectively λ_ex=443 nm and λ_ex=481 nm (Pr:³H₄→³P₂, ³H₄→³P₀). This indicated the existence of Pr³⁺→Sm³⁺ energy transfer in (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors.     

Tunable emission of single-phased NaY(WO4)2:Sm3+ phosphor based on energy transfer

A series of NaY(WO₄)₂:Sm³⁺ phosphors were prepared by high temperature solid state reaction. When excited by ultraviolet and blue light, their emission spectra cover entirely visible light region, due to intrinsic luminescence of WO₄^2- group as well as Sm³⁺ 4f-4f transitions. White light emission was obtained from NaY_0.99Sm_0.01(WO₄)₂ phosphor under radiation of 265 nm UV light, and intense yellow and red emission from ⁶H_{J(J=5/2, 7/2, 9/2)} transitions were observed when pumped Sm^{3+ 4}G_5/2 by 405 nm blue light. With incorporation of Sm³⁺ into NaY(WO₄)₂ host, higher-level emission from Sm³⁺ at 650 nm was generated by energy transfer from WO₄^2- to Sm³⁺ under excitation of 265 nm. The corresponding energy transfer mechanism was demonstrated to be a dipole-dipole interaction. In addition, tunable emission from blue to white and, finally, to red was realized by increasing Sm³⁺ doping concentration. The band gap of NaY(WO₄)₂ calculated from diffuse reflection spectra indicates a semiconducting character. All these results show that NaY_1−xSm_x(WO₄)₂ phosphor provides promising application for conversion of frequencies emitted by UV or blue LEDs.     

Luminescence characteristics and J-O analysis of BaWO4:3%Sm3+ crystal for yellow phosphors

Yellow emitting BaWO₄:3% Sm³⁺ phosphor was synthesized by a low-temperature molten salt method in LiNO₃-KNO₃. The prepared powders were characterized by X-ray diffraction (XRD), optical absorption and photoluminescence (PL) techniques. The crystal structure and related parameters were analyzed in detail by Rietveld refinement. The Judd–Ofelt (J-O) theory, which is used to explain the yellow emission mechanism and examine its luminescence properties, was applied to analyze the oscillator strengths, branching ratios, radiative lifetimes and transition probabilities of the BaWO₄:3%Sm³⁺ system. PL spectrum presented three prominent emission bands located at 562, 599 and 645 nm which are corresponding to the transitions from ⁴G_5/2 to ⁶H_5/2, ⁶H_7/2 and ⁶H_9/2, respectively. The CIE coordinates and correlated color temperature of the sample were also evaluated.     

The optical properties and the natural lifetime calculation of a Sm(III) complex

The photophysical properties of the complex Sm(PM)₃(TP)₂ [PM = 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone, TP = triphenyl phosphine oxide] are determined in crystal state, and energy transfer process is modeled for ligands to center Sm(III) ion. The characteristic luminescence of Sm(III) is sensitized by PM and TP, and most of transitions from excited state ⁴G_5/2 of Sm³⁺ are detected. According to the Judd–Ofelt theory, values of three oscillator strength parameters were obtained. The radiative transition rates for the emission from ⁴G_5/2 to the lower manifolds were obtained, and calculated radiative lifetime of the ⁴G_5/2 manifold is 3.1 ms. The corresponding fluorescence quantum efficiency is 2.7%.     

Structure,Judd-Ofelt analysis and spectra studies of Sm3+-doped MO-ZnO-B2O3–P2O5 (M = Mg,Ca, Sr,Ba) glasses for reddish-orange light application

In the present work, a series of Sm³⁺-doped MO-ZnO-B₂O₃–P₂O₅ (M = Mg, Ca, Sr, Ba) glasses were prepared. The glass structure and luminescence properties were investigated by XRD, DSC, IR, absorption spectroscopy, Judd-Ofelt theory and photoluminescence spectra. The J-O parameters of Sm³⁺-doped glasses follow the trend of Ω₄＞Ω₆＞Ω₂. Under the excitation of 401 nm Xenon lamp, Sm³⁺-doped glasses exhibited four emissions from the transitions of ⁴G_5/2→⁶H_J/2 (J = 5, 7, 9, 11) in the visible spectra. The luminous intensity of Sm³⁺ increases with the asymmetry in local environments and decreases with the increasing radius of the alkaline-earth cation. Among the as-prepared glass, the Sm³⁺-doped glass containing magnesium oxide exhibits higher values of stimulated emission cross-section (2.18 × 10⁻²¹ cm²), gain bandwidth (1.40 × 10⁻²⁷ cm³), and optical gain (3.83 × 10⁻²⁴ cm²). All the Sm³⁺-doped glasses show intense orange light in the CIE 1931 chromaticity diagram with a high color purity exceeding 99%. In addition, the time-resolved emission spectra reveal the decay process of the Sm³⁺ ions for the transitions ⁴G_5/2 → ⁶H_7/2 and ⁴G_5/2 → ⁶H_9/2 in the glass containing magnesium oxide. It suggests that Sm³⁺-doped alkaline-earth zinc borophosphate glasses could be a potential candidate for reddish-orange light-conversion fluorescent materials based on the ultraviolet light-emitting diode.     

Enhancement of up-conversion emission and emerging cool white light emission in co-doped Yb3+/ Er3+: Li2O-LiF-B2O3-ZnO glasses for photonic applications

A series of co-doped (Yb³⁺/Er³⁺): Li₂O-LiF-B₂O₃-ZnO glasses were prepared by standard melt quenching technique. Structural and morphological studies were carried out by XRD and FESEM. Phonon energy dynamics have been clearly elucidated by Laser Raman analysis. The pertinent absorption bands were observed in optical absorption spectra of singly doped and co-doped Yb³⁺/Er³⁺: LBZ glasses. We have been observed a strong up-conversion red emission pertaining to Er³⁺ ions at 1.0 mol% under the excitation of 980 nm. However, the up-conversion and down conversion (1.53 µm) emission intensities were remarkably enhanced with the addition of Yb³⁺ ions to Er³⁺: LBZ glasses due to energy transfer from Yb³⁺ to Er³⁺. Up-conversion emission spectra of co-doped (Yb³⁺/Er³⁺): LBZ glasses exhibits three strong emissions at 480 nm, 541 nm and 610 nm which are assigned with corresponding electronic transitions of ²H_9/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 respectively. Consequently, the green to red ratio values (G/R) also supports the strong up-conversion emission. The Commission International de E′clairage coordinates and correlated color temperatures (CCT) were calculated from their up-conversion emission spectra of co-doped (Yb³⁺/Er³⁺): LBZ glasses. The obtained chromaticity coordinates for optimized glass (0.332, 0.337) with CCT value at 5520 K are very close to the standard white colorimetric point in cool white region. These results could be suggested that the obtained co-doped (Yb³⁺/Er³⁺): LBZ glasses are promising candidates for w-LEDs applications.     

Structural,optical, and spectroscopic properties of Er3+-doped TeO2–ZnO–ZnF2 glass-ceramics

Transparent fluorotellurite glass-ceramics have been obtained by heat treatment of precursor Er-doped TeO₂–ZnO–ZnF₂ glasses. ErF₃ nanocrystals nucleated in the glass-ceramics have a typical size of 45 ± 10 nm. Based on the Judd-Ofelt theory, the main radiative parameters for the ⁴I_13/2 → ⁴I_15/2 transition have been obtained. The split of the absorption and emission bands and the reduction of the Ω₂ parameter, as compared to the glass, confirm the presence of Er³⁺ ions in a crystalline environment in glass-ceramic samples. The analysis of the ⁴I_13/2 decays suggests that a fraction of Er³⁺ ions remains in a glass environment while the rest forms nanocrystals. For the glass-ceramics, intense red and green upconversion emissions were observed with an enhancement of the ⁴F_9/2 → ⁴I_15/2 red one compared to the glass sample. The temporal evolution of the red emission together with the excitation upconversion spectra suggests that energy transfer processes are responsible for the enhancement of the red emission.     

Synthesis,crystal structure and temperature dependent luminescence of Eu3+ doped SrGd2O4 host: An approach towards tunable red emissions for display applications

In the present paper, an investigation on the structural and photoluminescence (PL) properties of SrGd₂O₄:Eu³⁺ ceramic phosphors synthesized by homogeneous precipitation method followed by combustion process has been reported. The samples, annealed at 1200 °C, were crystallized into orthorhombic phase without any impurities. Microscopic studies revealed the irregular morphology of the obtained ceramic phosphor particles having sizes in the range of 0.3–3 µm. The characteristic photoluminescence properties and decay curves were studied in detail as a function of Eu³⁺ concentration and temperature. The Eu³⁺ doped ceramic samples illuminated with UV light revealed the characteristic red luminescence corresponding to ⁵D₀→⁷F_J transitions of Eu³⁺. The concentration quenching phenomenon of Eu³⁺ ions in the present host, analyzed in the light of ion-ion interaction, indicated multipolar interaction between Eu³⁺ ions. Finally, the intensity parameters (Ω₂, Ω₄) and various radiative properties such as stimulated emission cross-section (σ_e), gain band-width (σ_e×Δλ_eff) and optical gain (σ_e×τ_exp) of Eu³⁺ in the SrGd₂O₄ ceramic phosphors have been calculated by using Judd-Ofelt theory. The present phosphor system exhibited efficient red emission with high red color purity (95%) and adequate thermal stability even at 200 °C. Present research broadly indicated the suitability of SrGd₂O₄:Eu³⁺ ceramic phosphor for display applications.     

Raman spectroscopy investigation of the H content of heated hard amorphous carbon layers

We revisit here how Raman spectroscopy can be used to estimate the H content in hard hydrogenated amorphous carbon layers. The H content was varied from 2 at.% to 30 at.%, using heat treatments of a a-C:H, from room temperature to 1300 K and was determined independently using ion beam analysis. We examine the correlation of various Raman parameters and the consistency of their thermal evolution with thermo-desorption results. We identify a weak band at 860 cm^− 1 attributed to H bonded to C(sp²). We show that the H_D/H_G parameter (height ratio between the D and G bands) is quasi-linear in the full range of H content and can thus be used to estimate the H content. Conversely, we show that the m/H_G parameter (ratio between the photoluminescence background, m, and the height of the G band), often used to estimate the H content, should be used with care, first because it is sensitive to various photoluminescence quenching processes and second because it is not sensitive to H bonded to C(sp²).     

Synthesis and photoluminescence properties of the high-brightness Eu3+-doped Sr3Y(PO4)3 red phosphors

A series of red-emitting phosphors Eu³⁺-doped Sr₃Y(PO₄)₃ have been successfully synthesized by conventional solid-state reaction, and its photoluminescence properties have been investigated. The excitation spectra reveal strong excitation bands at 392 nm, which match well with the popular emissions from near-UV light-emitting diode chips. The emission spectra of Sr₃Y(PO₄)₃:Eu³⁺ phosphors exhibit peaks associated with the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions of Eu³⁺ and have dominating emission peak at 612 nm under 392 nm excitation. The integral intensity of the emission spectra of Sr₃Y_0.94(PO₄)₃:0.06Eu³⁺ phosphors excited at 392 nm is about 3.4 times higher than that of Y₂O₃:Eu³⁺ commercial red phosphor. The Commission Internationale de l’Eclairage chromaticity coordinates, the quantum efficiencies and decay times of the phosphors excited under 392 nm are also investigated. The experimental results indicate that the Eu³⁺-doped Sr₃Y(PO₄)₃ phosphors are promising red-emitting phosphors pumped by near-UV light.     

Luminescent Er3+ doped transparent alumina ceramics

We report on successful preparation of Er³⁺ doped transparent alumina (0.1–0.17 at.%) exhibiting visible light photoluminescence using wet shaping method and hot isostatic pressing. The effects of dopant amount, type of doping powder and powder pre-treatment on final microstructure, real in-line transmittance and photoluminescence characteristics were studied.The real in-line transmittance ranged between 28 and 56%, depending on processing parameters. The transparency decreased with increased amount of dopant. The decrease is dependent on the type of doping powder and its pre-treatment.The photoluminescence spectra measured in both visible and NIR region showed typical emission bands due to the presence of Er³⁺ ions. The decay profiles of the ⁴S_3/2 → ⁴I_15/2 transition were fitted with a 2-exponential function, with faster component in the range of 360–700 ns and slower component around 1.6-2.4 μs. The intensity of emissions and lifetime of the ⁴S_3/2 level decrease significantly with increasing concentration of Er³⁺ ions.     

Biocompatibility and photoluminescence of Sm3+-doped SiO2-Gd2O3: A promising non-toxic red phosphor to plasmatic membrane tracking

Sm³⁺ doped SiO₂-Gd₂O₃ composites were obtained by a sol-gel process, and the ideal percentage of Sm³⁺ was evaluated for bioimaging applications. By XRD, a formation of Gd₂O₃ cubic materials was observed, and TEM shows that Gd₂O₃ particles are dispersed in a SiO₂ lattice. PLE spectra confirm the main absorption bands in the UV region and emission shows the most efficient excitation at 275 nm. PL results reveal the incorporation of Sm³⁺ in Gd₂O₃ structures and lead to the understanding of the efficient energy transfer between Gd³⁺ and Sm³⁺ in the materials. The mechanism is proposed and discussed. CIE plotting shows color coordinates in the orange and red regions, mainly dependent on the excitation source. Sm³⁺ positions in Gd₂O₃ are discussed using the results obtained in the emission spectra. Materials presented high lifetime values, between 1.53 and 1.82 ms. The phosphors show tunability properties and better performance as red phosphors when excited at 275 nm. Cell viability was performed and the material is non-toxic. The materials were evaluated as biological markers, and present fluorescence under rhodamine emission filters. SiO₂-Gd₂O₃:Sm³⁺ demonstrates a good viability index and co-localizes with membrane cell markers, showing a promising material for cell tracking. The material also demonstrates potential for cancer targeting.     

Photoluminescence,photochromism, and reversible luminescence modulation behavior of Sm-doped Na0.5Bi2.5Nb2O9 ferroelectrics

Sm-modified Na_0.5Bi_2.5Nb₂O₉ ceramics can simultaneously exhibit both visible light-driven photochromism and photoluminescence. Upon visible light irradiation, these materials change their color from green to dark gray, while exhibiting a strong red emission at 603 nm due to the ⁴G_5/2 → ⁶H_7/2 transition, whose emission intensity strongly depends on the irradiation wavelength, intensity, and time, and significantly decreases with increasing irradiation time and intensity. By alternating visible light or sunlight (λ > 400 nm) irradiation and thermal stimulus, both luminescence and absorption intensity can be reversibly switched without any significant degradation between the two colored and bleached states, with excellent reproducibility. On the basis of the trapped charge carrier and exponential relaxation decay models, we herein provide a detailed understanding of the photochromism and luminescence modulation mechanisms.     

Spectroscopic and photoluminescence characteristics of Sm3+ doped calcium aluminozincate phosphor for applications in w-LED

Monophase Calcium Aluminozincate (Ca₃Al₄ZnO₁₀) phosphor doped with Sm³⁺ ions by varying concentrations have been prepared at 1300 °C using conventional solid state reaction technique. The crystal structure and phase analysis of the as-prepared phosphor has been carried out by X-ray Diffraction (XRD) studies. Morphology and functional groups present in the phosphor have been investigated thoroughly by using Scanning Electron Microscope (SEM) and Fourier Transform Infrared (FT-IR) spectral measurements, respectively. Under 401 nm excitation, the as-prepared phosphor exhibit intense visible orange emission at 601 nm. It has been observed that 1.0 mol% of Sm³⁺ ions concentration is optimum to give intense visible orange emission. The PL analysis reveals that the dipole-dipole interaction is primarily responsible for the concentration quenching observed beyond 1.0 mol% of Sm³⁺ ions. The TR-PL study reveals a bi-exponential behavior of decay curves with an average lifetime of the order of microseconds. The CIE coordinates (x=0.574 and y=0.424) measured for the optimized phosphor are very close to the intense orange emission coordinates specified by Nichia Corporation developed Amber LED NSPAR 70BS (0.570, 0.420). The spectroscopic, PL and TR-PL studies suggest the potential use of Sm³⁺ doped calcium aluminozincate phosphors for display and white light emitting devices.     

Characterizations and optical properties of Sm3+-doped Sr2SiO4 phosphors

Optical properties of samarium-doped strontium orthosilicate for near ultra-violet excitation are studied. Sr₂SiO₄:Sm³⁺ phosphor is synthesized by using the solid-state reaction method. The structure and physical properties of the phosphor are characterized by using X-ray diffractometer, scanning electron microscope, UV–visible spectrophotometer, high-resolution secondary ion mass spectrometer, and X-ray photoelectron spectrometer. Optical properties are studied by taking excitation and emission spectra. A strong red-orange luminescence corresponding to ⁴G_5/2 → ⁶H_7/2 transition of Sm³⁺ for near ultra-violet excitation is observed. It is found that Sr₂SiO₄:Sm³⁺ is a red-orange emitting phosphor and has higher efficiency for the operation with near ultra-violet excitation.     

Enhancement of luminescence properties and the role of ZnO in Tb3+ ions doped zinc aluminum phosphate glasses

Terbium ion doped zinc aluminum phosphate (ZAP) glasses with composition (90−x)((90−y)P₂O₅–10Al₂O₃–yZnO)–xTb₂O₃ (x=0.5–9 in mol% and y=30, 35, 40 in mol%) have been prepared by melt quenching method, and the effects of the Tb₂O₃ and ZnO content on the luminescence properties have been studied by photoluminescence spectroscopies. It was found that the green emission peaked at 544 nm is significantly enhanced under higher Tb₂O₃ content, meanwhile the sensitization effect of ZnO content is confirmed from the enhanced main emission. The quenching effect attributed to the resonant energy transfer through the cross-relaxation mechanism is observed when Tb₂O₃ concentration is beyond 2.5 mol% due to the fact that more Tb³⁺ ions enhance the 4f→5d and 4f→4f electronic transitions through the dipole–dipole (d–d) interaction. Also, ZnO plays a role of the disperser to prevent non-radiative de-excitation process. A characteristic luminescence image of the (100−x)(60P₂O₅–10Al₂O₃–30ZnO)·xTb₂O₃ series glasses under UV excitation at 366 nm is presented for the first time, and the transition of luminescence suggests that the Tb³⁺-doped ZAP glasses are suitable for green and dual-color blue/green LED applications by modulation of Tb and ZnO composition.     

Efficient near-infrared to visible and ultraviolet upconversion in polycrystalline BiOCl:Er3+/Yb3+ synthesized at low temperature

Er³⁺/Yb³⁺ co-doped BiOCl poly-crystals were synthesized by the conventional solid state method at 500 °C, which exhibited good crystalline and low phonon energy. Under 980 nm excitation, the samples showed intense red upconversion (UC) luminescence (Er³⁺: ⁴F_9/2→⁴I_15/2) as well as other four UC emission bands, including ultraviolet (UV) emission at 380 nm, violet emission at 411 nm, green UC emissions at 525 and 545 nm and near-infrared (NIR) emission between 800 and 850 nm, corresponding to the transitions of ⁴G_11/2, ²H_9/2, ²H_11/2, ⁴S_3/2 and ⁴I_9/2→⁴I_15/2 of Er³⁺, respectively. Interestingly, including the violet and green UC emissions, the red one originated a nearly three-photon process in this system, and a possible UC mechanism was proposed for the enhanced red emission.