Active Rare Earth Research Articles

Enhancing low-energy X-ray excited afterglow in lanthanide-doped fluoride core@shell nanoparticles for autofluorescence-free imaging

Lanthanide-doped fluoride nanoparticles (NPs) exhibit tunable X-ray excited afterglow (XEA), holding great promise for autofluorescence-free flexible X-ray imaging. However, materials with low atomic numbers, while sensitive to low-energy X-ray photons, suffer from weak X-ray absorption coefficients. This poses a significant challenge in achieving high-performance XEA with minimized radiation risk. In this study, we enhance the low-energy XEA of lanthanide activators by engineering the interfacial defect formation energy (Ef) in CaF2-based heterogeneous core/shell nanoarchitectures. Mechanistic investigations demonstrate that a large lattice misfit between the core and shell reduces the interfacial defect Ef, facilitating the formation of Frenkel defects and significantly increasing XEA intensity after low-energy X-ray irradiation. Specifically, the heterogeneous CaF2:Tb@CaLuF5 core/shell NPs, with a misfit of 3.382 %, exhibit approximately ∼ 8.9 times higher XEA intensity compared to the CaF2:Tb@CaF2 homogeneous core/shell NPs at 10 kV. Furthermore, integrating the CaF2:Tb@CaLuF5 NPs into a flexible scintillation screen enables XEA-based delayed imaging with high spatial resolution, up to approximately 14.2 lp mm−1, and an autofluorescence-free background. These findings advance the development of superior low-energy XEA materials and pave the way for autofluorescence-free three-dimensional X-ray imaging.

Simultaneously enhanced photoluminescence and persistent luminescence in SrLaAlO4: Tb type layered perovskite via Gd3+ codoping

Gd3+ co-doping is effective to enhance the photoluminescence of rare earth activators in various host due to energy transfer, however, it is rarely reported via such strategy to regulate persistent luminescence properties. In this work, Gd3+ was co-doped into the SrLaAlO4: Tb persistent luminescence phosphors, and it is found that the photoluminescence and persistent luminescence of the products can be simultaneously improved. The results indicate that as the doping concentration of Gd3+ increases, the particle diameters increase which contributes the increased luminescence. Additionally, an energy transfer process from Gd3+ to Tb3+ ions was observed, which enhances the emission of Tb3+ ions. Furthermore, the persistent luminescence properties of the synthesized phosphors were improved. When the UV light source is turned off, the persistent luminescence of SrLaAlO4: 0.03Tb3+, xGd3+ (x = 0.00–0.97) can last for more than 2 h, which is 100 % enhanced compared to SrLaAlO4: 0.03Tb3+. The trap distribution of SrLaAlO4: 0.03Tb3+, xGd3+ (x = 0.00–0.97) phosphors was analyzed by thermoluminescence. It is found that after the substitution of La3+ with Gd3+, the trap position shifted towards higher temperatures and the trap concentration increased. The initial intensity of the persistent luminescence was also enhanced after Gd3+ co-doping. Based on the experimental findings, the luminescence and persistent luminescence mechanism of SrLaAlO4: 0.03Tb3+, xGd3+ (x = 0.00–0.97) phosphors were described and discussed.

Spectroscopic analysis of CaGd2(WO4)4 phosphor doped with Nd3+ and Yb3+ for NIR applications

Considering the important applications of near infrared light sources, phosphors emitting in this region are always explored. New hosts are studied for this purpose. Keeping with this tradition we have investigated CaGd2(WO4)4 host by using SSR method. XRD pattern of the as prepared compound confirms the monoclinic crystal structure with I2/b space group. Well known lanthanide activators Nd3+ and Yb3+ led to the desired infrared emission. Nd3+ yielded emission by itself under f-f excitation while Yb3+ depended upon the energy transfer from Nd3+ and to yield near infrared light. The host also provided sensitization. However this is very weak compared to the intensities of the f-f transitions of Nd3+. PL and PLE spectra as well as the mechanism of energy transfer is explained on the basis of the known energy level diagrams. Prepared phosphor have potential application in the field of Solid State Laser and bio-imaging.

Upconverting Ultra-Thin Bi2O2CO3 Nanosheets for Synergistic Photodynamic Therapy and Radiotherapy.

Synergistic therapy has become the major therapeutic method for malignant tumors in clinical. Photodynamic therapy (PDT) and radiotherapy (RT) always combine together because of their identical anti-tumor mechanisms, that is reactive oxygen species are generated by the use of radiosensitizers after irradiation by X-ray to efficiently kill cancer cells, PDT also follows similar mechanism. Full exposure of energy-absorbing species in nanomaterials to X-ray or near-infrared light irradiation makes the energy interchange between nanomaterials and surrounding H2O or dissolved oxygen easier, however, it remains challenging. Herein, an ultrathin two-dimensional (2D) nanosheet (NS) is developed, Bi2O2CO3, doped with lanthanide ions to give out upconversion luminescence, where the high Z elements Bi, Yb, and Er promote the radio-sensitizing effect. To the surprise, lanthanide activator ions gave out completely different luminescence properties compared with traditional upconversion nanoparticles. Less dopant of Er ions in nanosheets lattice resulted in brighter red emission, which provides more efficient PDT. Under RT/PDT combined treatment, NS shows a good tumor growth-inhibiting effect. In addition, synergistic therapy requires lower radiation dose than conventional radiotherapy and lower light power than single photodynamic therapy, thus greatly reducing radiation damage caused by RT and thermal damage caused by PDT.

Synthesis of NaYbF4:Er nanocrystals with controllable size, morphology, and multicolor upconversion luminescence for Anticounterfeiting applications

The dopant concentration of lanthanide ions plays one of the critical roles to manipulate size/morphology, photon population pathway, or luminescence color/intensity in upconversion nanoparticles (UCNCs), which have a significant effect on their application developments. Herein, a strategy is demonstrated for simultaneous size, morphology and multicolor luminescence tuning in the single doped lanthanide activator Er3+ ion system through simply tuning the concentration of Er3+ ions. The doping of different Er3+ ion amounts in NaYbF4:Er nanocrystals can control nanoparticle size (from several hundreds to tens of nanometers) and morphology. Moreover, multicolor upconversion luminescence involving green, yellow, orange and red can be obtained in the NaYbF4:Er UCNCs by changing the excitation power density of 980 nm laser. Mechanistic studies reveal the size and morphology evolution process as well as saturation/cross relaxation effects induced tunable multicolor emissions. These nanocrystals have demonstrated promising potential applications in anticounterfeiting. Our results not only provide a simple and feasible route for simultaneous size/morphology control and multicolor upconversion luminescence tuning, but also can further expand the utility of UCNCs in the frontier applications ranging from optical encoding to information security.

Augmentation of NIR Circularly Polarized Luminescence Activity in Shibasaki-Type Lanthanide Complexes Supported by the Spirane Sphenol.

We report two new circularly polarized luminescence (CPL)-active lanthanide complexes emissive in the near-infrared (NIR) region; using sphenol as a supporting ligand, we provide the first reported example of an NIR-emissive lanthanide complex supported by a chiral spirane. Inclusion of a quaternary carbon to impart axial chirality results in dramatic augmentation of the CPL strength of the resultant sphenolate complexes (glum ≤ 0.77 for [(sphenol)3ErNa3(thf)6]) compared to that of their contemporary biaryl-based axially chiral analogues (glum ≤ 0.47 for [(binol)3ErNa3(thf)6]). Despite similar structural parameters, the rigid spiro carbon of sphenol enables the strongest dissymmetry factors observed to date from Shibasaki-type complexes for both Yb and Er. We also demonstrate the sensitivity of the reported chiroptical measurements to small variations in instrumental parameters, such as bandpass, and suggest a standardized method or at least that additional detail should be included in future reports to allow for direct comparisons between newly published CPL emitters.

Luminescence of some lanthanides in synthetic yttrium gagarinite (NaCaYF6)

NaCaYF6 is the formula for gagarinite. Noting the lack of luminescence studies in this material, we synthesized it using the hydrothermal method and investigated the luminescence of several lanthanides. Characteristic luminescence of Eu[Formula: see text], Dy[Formula: see text], Sm[Formula: see text] and Tb[Formula: see text] was observed. Detailed results on photoluminescence emission and excitation spectra, lifetime, chromaticity coordinates and concentration dependence of emission intensity are presented. Except for Tb[Formula: see text], which exhibits f-d excitation, the luminescence of other activators got quenched at 1[Formula: see text]mol % concentration. Eu[Formula: see text] emission in this host was peculiar, in that the emissions from higher 5D states were observed. Luminescence characteristics are explained using the known energy level diagrams for the lanthanide activators.

Ligand Chirality Transfer from Solution State to the Crystalline Self-Assemblies in Circularly Polarized Luminescence (CPL) Active Lanthanide Systems.

The synthesis of a family of chiral and enantiomerically pure pyridyl-diamide (pda) ligands that upon complexation with europium [Eu(CF3SO3)3] result in chiral complexes with metal centered luminescence is reported; the sets of enantiomers giving rise to both circular dichroism (CD) and circularly polarized luminescence (CPL) signatures. The solid-state structures of these chiral metallosupramolecular systems are determined using X-ray diffraction showing that the ligand chirality is transferred from solution to the solid state. This optically favorable helical packing arrangement is confirmed by recording the CPL spectra from the crystalline assembly by using steady state and enantioselective differential chiral contrast (EDCC) CPL Laser Scanning Confocal Microscopy (CPL-LSCM) where the two enantiomers can be clearly distinguished.

Dual heterogeneous interfaces enhance X-ray excited persistent luminescence for low-dose 3D imaging

Lanthanide-doped fluoride nanoparticles (NPs) showcase adjustable X-ray-excited persistent luminescence (XEPL), holding significant promise for applications in three-dimensional (3D) imaging through the creation of flexible X-ray detectors. However, a dangerous high X-ray irradiation dose rate and complicated heating procedure are required to generate efficient XEPL for high-resolution 3D imaging, which is attributed to a lack of strategies to significantly enhance the XEPL intensity. Here we report that the XEPL intensity of a series of lanthanide activators (Dy, Pr, Er, Tm, Gd, Tb) is greatly improved by constructing dual heterogeneous interfaces in a double-shell nanostructure. Mechanistic studies indicate that the employed core@shell@shell structure could not only passivate the surface quenchers to lower the non-radiative relaxation possibility, but also reduce the interfacial Frenkel defect formation energy leading to increase the trap concentration. By employing a NPs containing flexible film as the scintillation screen, the inside 3D electrical structure of a watch was clearly achieved based on the delayed XEPL imaging and 3D reconstruction procedure. We foresee that these findings will promote the development of advanced X-ray activated persistent fluoride NPs and offer opportunities for safer and more efficient X-ray imaging techniques in a number of scientific and practical areas.

Multicolor Tunable Upconversion Luminescence via Near‐Infrared Manipulation of Population Pathways of Er3+ Ions Excited‐State Levels for Volumetric Color Displays

AbstractPrecise control over multicolor luminescence of upconversion nanoparticles (UCNPs) is of significant importance for their applications in widespread fields of research. However, realizing the tunable emissions in single UCNPs with a single lanthanide element remains a great challenge. Herein, without multiple lanthanide elements, a new strategy for the regulation of the excited‐state level population pathways of the same lanthanide activator Er3+ ion to obtain multicolor‐tunable upconversion luminescence is proposed through utilizing 980 nm coupled 1973 nm synergistic excitation. Unlike typical single wavelength excitation, the synergistic excitation may affect population pathways of the excited‐state level of Er3+ ion by adjusting excitation wavelength and power density, resulting in a dynamically adjustable change in luminescence color output. Notably, multicolor luminescence involving green, chartreuse, yellow, orange, and red can be tuned dynamically in the NaYF4:Er3+ single UCNPs by using the tunable 980/1973 nm synergistic excitation. This dynamic luminescence color variation from these UCNPs has demonstrated promising potential applications in volumetric color display. The results provide a new approach to achieve multicolor‐tunable upconversion luminescence at single nanoparticles level and open up the possibility of developing true three‐dimensional volumetric color display technologies with resolution at the nanometer range.

Effect of neodymium ions on the photosensitivity of photo-thermo-refractive glass

Neodymium doping of photo-thermo-refractive (PTR) glass leads to a fast non-radiative depopulation of excited states of cerium ions, which are responsible for the glass photosensitivity. The non-radiative energy transfer from cerium to neodymium ions results in a decrease in the efficiency of photoelectron generation under UV irradiation. Emission spectra and fluorescence decay curves of cerium ions under UV excitation were investigated. Absorption spectra of the glasses were obtained as well to distinguish the reabsorption processes and the non-radiative energy transfer mechanisms. It was found that as Nd2O3 concentration increases from 0 to 2 mol%, cerium ions average lifetime decreases from 44.5 to 28 ns, while the energy transfer efficiency reaches 37 %. It was also found that Förster resonance energy transfer may compete with other relaxation mechanisms and the Förster distance for the Ce3+-Nd3+ pair in PTR glass is ∼0.33 nm. This study has important implications for future research; it informs future studies on optimizing the photosensitivity of the PTR glass and choosing rare-earth activators.

Spectroscopic and Lasing Properties of Highly Concentrated Glasses

A method has been advanced for the quantitative separation of the degradation channels of the electron-excitation energy of rare-earth activators, which is based on measurements of the duration of activator luminescence and of the absorption coefficient of OH-groups in concentration series of glasses. The optimal neodymium concentration has been established for obtaining the maximum gain in phosphate glasses. Preliminary lasing tests of the concentration series of phosphate and also silicate glass with a neodymium concentration of approximately 2.3 × 1020 ions cm–3 have been performed.

Er3+-Sensitized Upconversion/Down-Shifting Luminescence in Metal-Organic Frameworks.

Photoluminescent metal-organic frameworks (MOFs) are used as optical materials with excellent properties, of which the lanthanide-doped MOFs are able to emit in a broad region from visible to near-infrared due to their unique 4f-orbital electronic structure. Herein, Er3+ and Y3+ ions are selected as the metal centers of the MOFs and Er3+ is used as a sensitizer to absorb 980 nm excitation light. At the same time, Er3+ ions also act as activators that emit upconverting visible light and down-shifting near-infrared light. In addition, Tm3+, Ho3+, and Eu3+ ions were individually doped into the Er3+-doped MOFs to investigate the variation of energy-transfer paths in the presence of different lanthanide activators. Finally, the pathway of energy transfer in these Er3+-sensitized luminescent-MOFs was summarized. This work provides new insights for further development of both upconversion and down-shifting luminescence of MOFs.

Study of adsorption and immobilization of Cs+, Sr2+, Co2+, Pb2+, La3+ ions on Na-Faujasite zeolite transformed in solid state matrices

Zeolites have become promising adsorbents for wastewater treatment due to their enhanced adsorption capacity, stability of crystalline structure, high porosity and surface area. One of the primary goals of our study was to assess the effectiveness of employing NaY zeolite as a sorbent and potential solid matrix for immobilizing radionuclides. In this study NaY faujasite zeolite was obtained by hydrothermal synthesis and characterized by X-Ray diffraction (XRD), N2 adsorption–desorption, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) methods. The prepared zeolite had NaY faujasite crystalline structure, characterized by developed surface area (370 m2/g) with micro-mesoporous structure, and spherical-like morphology with particles of 1–4 μm in diameter. The isotherms adsorption modeling on Cs+, Sr2+, Co2+, Pb2+ and La3+ ions was performed. The isotherm well described by Langmuir equation with maximum adsorption capacity of q(Cs+) = 1,9 mmol/g, q(Sr2+) = 3,75 mmol/g, q(Co2+) = 1,82 mmol/g, q(Pb2+) = 2,54 mmol/g, q(La3+) = 3,83 mmol/g. Thermal behavior of metal-saturated adsorbents by differential thermal analysis (DTA) and thermal gravimetric (TG) techniques was studied. Each metal examined in this paper is responsible for the stable formation of radionuclides (137Cs, 90Sr, 60Co, La - generally, the group of active lanthanides was modelled, Pb - uranium fission residues) that are generated during the operation of nuclear power plants. To optimize sintering regimes, it has been proposed to achieve sorption saturation of stable ions such as Cs, Sr, Co, La, and Pb and transfer them into solid matrices. It was shown that the consolidation temperature for the obtained samples varies in the range of 935–1040 °C.

Unexpected Expansion of Rare-Earth Element Mining Activities in the Myanmar–China Border Region

Mining for rare earth elements is rapidly increasing, driven by current and projected demands for information and energy technologies. Following China’s Central Government’s 2012 strategy to shift away from mining in favor of value-added processing, primary extraction has increased outside of China. Accordingly, changes in mineral exploitation in China and Myanmar have garnered considerable attention in the past decade. The prevailing assumption is that mining in China has decreased while mining in Myanmar has increased, but the dynamic in border regions is more complex. Our empirical study used Google Earth Engine (GEE) to characterize changes in mining surface footprints between 2005 and 2020 in two rare earth mines located on either side of the Myanmar–China border, within Kachin State in northern Myanmar and Nujiang Prefecture in Yunnan Province in China. Our results show that the extent of the mining activities increased by 130% on China’s side and 327% on Myanmar’s side during the study period. We extracted surface reflectance images from 2005 and 2010 from Landsat 5 TM and 2015 and 2020 images from Landsat 8 OLI. The Normalized Vegetation Index (NDVI) was applied to dense time-series imagery to enhance landcover categories. Random Forest was used to categorize landcover into mine and non-mine classes with an overall accuracy of 98% and a Kappa Coefficient of 0.98, revealing an increase in mining extent of 2.56 km2, covering the spatial mining footprint from 1.22 km2 to 3.78 km2 in 2005 and 2020, respectively, within the study area. We found a continuous decrease in non-mine cover, including vegetation. Both mines are located in areas important to ethnic minority groups, agrarian livelihoods, biodiversity conservation, and regional watersheds. The finding that mining surface areas increased on both sides of the border is significant because it shows that national-level generalizations do not align with local realities, particularly in socially and environmentally sensitive border regions. The quantification of such changes over time can help researchers and policymakers to better understand the shifting geographies and geopolitics of rare earth mining, the environmental dynamics in mining areas, and the particularities of mineral extraction in border regions.

Synthesis, characterization and enhanced photoluminescence and temperature dependence of ZrO2:Dy3+ phosphors upon incorporation of K+ ions

This study reports the successful synthesis and comprehensive characterization of ZrO2:Dy3+ phosphors with the incorporation of K+ ions. The introduction of Dy3+ and K+ in the ZrO2 lattice as lanthanide activators demonstrates its potential as an efficient host material. The structural integrity of ZrO2 remains unaltered following the doping process. Fourier-transform infrared spectroscopy (FTIR) analysis confirms the presence of Zr-O and O-H stretching, along with H2O bending modes in the phosphor sample. The wide luminescence band seen at 460 nm is attributed to luminescence defects in the ZrO2 induced by oxygen, and the presence of water molecules. Photoluminescence (PL) spectra analysis reveals pronounced emission peaks at 491 and 578 nm, corresponding to 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions, respectively, upon excitation at 349 nm. Optimizing the Dy3+ doping concentration to 0.4 wt% and achieving a critical distance of 31.82 Å resulted in efficient energy transfer. Notably, co-doping K+ as a charge compensator significantly enhances the luminescence intensity. Moreover, at lower temperatures, direct excitation of Dy3+ ions through our pump wavelength, coupled with exciton-mediated energy transfer, leads to a remarkable increase in PL intensity. Tailoring the doping concentrations effectively shifts the emission spectrum of the phosphor mixture, aligning with the standard white light illumination coordinates (0.333, 0.333). This property positions the material as a promising candidate for applications in white light-emitting diodes (WLEDs) and various high-quality lighting applications. The enhanced photoluminescence and temperature dependence observed in ZrO2:Dy3+ phosphors upon the incorporation of K+ ions pave the way for their potential utilization in advanced luminescent devices.

STRUCTURAL DESIGN OF Eu<sup>2+</sup>-CONTAINING GLASS AND GLASS-CERAMICS BASED ON THE SYSTEM BaO–ZrO<sub>2</sub>–SiO<sub>2</sub>–MgF<sub>2</sub> FOR LED APPLICATION

For the first time, an approach to designing the structure of Eu2+ containing silicate glass-ceramics materials has been experimentally implemented, which consists in the fact that rare earth activator is introduced into various crystals formed during glass crystallization. Transparent Eu-containing glass and glass ceramics based on the system BaO–ZrO2–SiO2–MgF2 were prepared by the traditional glass melting method at 1450°C. The crystal structure and properties of materials were characterized by XRD analysis and photoluminescence spectroscopy during different stages of glass crystallization. It is shown that the simultaneous incorporation of Eu into different silicate crystals (Ba2SiO4, BaMgSiO4, and BaSiO3) formed during the glass crystallization leads to the formation of a material with a wide luminescence band in the visible part of the spectrum. The study of photoluminescence and luminescence excitation spectra of the glass suggests the possibility of energy transfer from Eu2+ to Eu3+ ions. The structures of Eu2+ luminescent centers are similar in the glass and glass-ceramics that is related to some phase separation in the glass before crystallization. The study of luminescence properties of prepared materials showed that these materials can be promising for the application in LEDs techniques.

Structural Confinement Induced Near‐Unity Quantum Yield for Single‐Band Ratiometric Thermometry

AbstractLuminescence quenching at high dopant concentration and temperature typically limits the brightness of luminescence materials, which remains a major obstacle in diverse technological applications, especially in the field of luminescence thermometry. In this work, a unique class of non‐concentration quenching double‐tungstate phosphors is reported that feature the near‐unity quantum yield of Tb3+ and Eu3+ emissions induced by the structural confinement effect. Mechanistic studies affirm that the activator ions can be isolated in NaYW2O8 crystal to confine the absorbed photon energy, leading to a relatively high quenching concentration of various lanthanide activators. By facilitating interionic cross‐relaxation at heavy dopant concentration, a remarkable thermal enhancement of Tb3+ emissions over 20‐fold upon the excitation of excited‐state absorption is recorded. In contrast, thermally quenched emissions are detected under the excitation of ground‐state absorption. This excitation wavelength‐dependent thermal behavior of Tb3+ emissions is harnessed for single‐band ratiometric thermometry, registering superior thermal sensitivity and resolution (Sr = 4.01% K−1, δT = 0.1 K). The advances in combating concentration and thermal quenching of luminescence materials provide exciting opportunities for flexible thermometry in real‐world sensing scenarios.

Optical properties and tunable luminescence of Ce3+/Dy3+ doped lithium borate glasses for photonic applications

Optical absorption and photoluminescence properties of novel lithium borate glasses, (B2O3)-(MO)-(Li2O)–(Bi2O3) where M stands for Ca, Mg or Sr, doped with Dy and Ce ions have been investigated. The fundamental optical absorption edge of these materials is observed in the region of 315–390 nm, and depends on the nature of alkaline-earth metals used as network modifiers. The photoluminescence spectra of Dy-doped glasses reveal two intensive emission bands in the visible range, which correspond to 4F9/2→6H15/2 (486 nm) and 4F9/2→6H13/2 (580 nm) transitions of Dy3+ ions. Ce-doped glasses show one broad band in the visible range, which corresponds to the 2D →2F5/2 (340 nm) transition of Ce3+ ions. Three photoluminescence lines (980 nm, 1010 nm and 1150 nm) attributed to the Dy3+ ions electronic transitions are observed in the near-IR region of the spectrum for Dy-doped glasses, while only one at 1150 nm is observed for the Dy/Ce co-doped glasses. Peculiarities of excitation energy transfer between rare-earth activator ions are discussed. These glasses are shown to be a promising host matrix for rare-earth doping.

Host sensitization of luminescence of lanthanide activators in NaBi(WO4)2

The synthesis and luminescence of a series of NaBi(WO4)2 activated with trivalent lanthanides Tb, Sm and Nd using the solid-state reaction method is reported. All samples were characterised by X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence (PL). The XRD study confirmed the tetragonal phase without any secondary phase. Particles of irregular shape ranging between 5 and 20 µm were observed. Elemental composition was obtained from EDAX and results were found consistent with the formula NaBi(WO4)2. The formation of single-phase NaBi(WO4)2 was again confirmed through these results. Elemental mapping indicated that all elements were uniformly distributed. The band gap was evaluated using Tauc’s. formula and was found from 5.6 eV to 5.91 eV which is higher than reported values (3.6 eV). For NaBi(WO4)2:Tb, excitation was monitored for 545 nm emission. Emission spectra upon excitation by 488 nm showed prominent lines around 545 and 549 nm. These are due to the transition 5D4 7F5. 5 mol.% Tb yielded maximum PL intensity. When 405 nm excitation is used for Sm3+ doped phosphor, lines can be seen in three groups around 564, 600 and 647 nm. The highest emission intensity is observed for Sm3+ concentration of 5 mol.% and quenching was observed for high values. A weak band could be seen in the excitation spectra which is distinct from the f-f lines. The position of this band is close to that observed in the reflectance spectra. Hence it is proposed that there is host sensitization, even though weak, of the lanthanide luminescence in this host. Sensitization is most probably due to Bi3+ Ln3+ energy transfer.