High-performance short-wave infrared (SWIR) phosphors are of increasing interest for phosphor-converted light-emitting diodes (pc-LEDs) used in sensing, imaging, and analytical applications. In this work, Li3Ba2Gd3(MoO4)8 (LBGMO) phosphors co-doped with Yb3+/Tm3+ and Yb3+/Ho3+ were developed as efficient near-infrared (NIR)-to-SWIR down-shifting (DS) materials. Phase purity and crystal structure were confirmed by X-ray diffraction, demonstrating successful incorporation of rare-earth ions into the LBGMO host lattice. Under 940 nm excitation, efficient sensitization by Yb3+ ions enables strong SWIR emission from both activator ions. The Yb3+/Tm3+ system exhibits broadband emission centered at approximately 1800 nm, originating from the Tm3+: 3F4 → 3H6 transition, whereas the Yb3+/Ho3+ system shows dominant emission near 2050 nm associated with the Ho3+: 5I7 → 5I8 transition. High photoluminescence quantum yields (PLQY) of 63% and 69% were achieved for the Yb3+/Tm3+ and Yb3+/Ho3+ phosphors, respectively, accompanied by efficient energy transfer from Yb3+ to Tm3+ (95%) and Ho3+ (96%). The moderate cut-off phonon energy of 930 cm-1 supports efficient population of the lower-energy SWIR-emitting states, while the rate of non-radiative relaxation remains sufficiently low to prevent effective competition with radiative transitions. Phosphor-converted LED devices using 940 nm excitation and fabricated with the developed phosphor conversion layers exhibited maximum wall-plug efficiencies of 1.6% for Yb3+/Tm3+ and 3.6% for Yb3+/Ho3+. Demonstration of SWIR imaging through visibly opaque materials and spectral overlap with water absorption bands confirms the potential application of these materials.

Mn[4+]-activated far-red emitting phosphors have emerged as a crucial substitute for traditional rare-earth-based luminescent materials. However, the design of Mn[4+]-type far-red phosphors with high quantum efficiency remains a pivotal challenge because manganese as a typical transition metal element is prone to valence changes, and simultaneously, the 3d-3d characteristic transition of the Mn[4+] ion is parity-forbidden. Aiming at this fact, in a Mn-doped Sr4AlNbO8 phosphor (SANO), we present a Ge[4+] coblending approach that not only facilitates the directional conversion of coexisting mixed-valence impurities toward Mn[4+] but also realizes the breaking of the parity-forbidden transition of Mn[4+]. DFT calculations and experimental results identify that the Ge[4+] ion can act as a modulator to induce the reconstruction of intrinsic matrix defects, which suppress the formation of Mn[2+] and Mn[5+] impurities. Furthermore, through a comprehensive analysis involving Mn K-edge XAFS spectroscopy, we demonstrate that the Mn[4+]/Nb[5+]-O[2-] bond in the (Mn[4+], Nb[5+])O6 octahedron will undergo asymmetrical elongation and shrinkage after introducing the Ge[4+] ion, which lowers inversion symmetry and thus improves the probability of the d-d transition of Mn[4+]. The optimal SANO:0.008Mn, 0.05Ge phosphor exhibits a nearly 300-fold PL intensity enhancement at 710 nm, and the quantum efficiency increases from 3% to 86% compared with the original SANO:0.008Mn sample. Actual growth of tomatoes is examined via a reflection-type sunlight-conversion fluorescent membrane as a sunlight-converting system based on the above phosphor. Compared with the blank control group, the fresh weights of tomatoes are increased by 21.89%. These results establish that the reported Mn[4+]-activated phosphor can hold potential applications for indoor plant cultivation.

Eu[3+]-activated LiNaSO4 phosphors were synthesized via a sol-gel technique and investigated to understand their structural, morphological, and luminescent properties. X-ray diffraction and Rietveld refinement confirmed the formation of a single-phase trigonal LiNaSO4 structure with high crystallinity and successful incorporation of Eu[3+] ions without disturbing the host framework, whereas FTIR spectra verified the presence of characteristic sulfate vibrational modes, and SEM analysis revealed agglomerated polycrystalline grains with well-defined boundaries. Photoluminescence measurements under 395-nm excitation showed intense red emission dominated by the hypersensitive [5]D0 → [7]F2 transition at 614 nm, indicating that Eu[3+] ions occupy noncentrosymmetric lattice sites. The emission intensity increased with dopant concentration up to 0.8 mol% and then decreased due to concentration quenching governed by multipolar interactions. CIE chromaticity analysis demonstrated deep red emission with high color purity and reduced correlated color temperature, supporting suitability for warm white LED applications. Judd-Ofelt analysis yielded an asymmetry ratio of 2.07 and an intensity parameter Ω2 = 1.43 × 10[-20] cm[2], confirming strong crystal field asymmetry and enhanced Eu-O covalency, which contribute to the observed intense red luminescence. These results establish LiNaSO4:Eu[3+] as a promising red-emitting phosphor for solid-state lighting and display technologies.

Yttrium is one of the lesser-known critical elements, but it has recently gained significant market attention due to a dramatic price increase of up to 1400% in Europe. Although its primary application is in phosphors (e.g., in LEDs), modern society heavily depends on these technologies, making yttrium indispensable. However, the limited availability of yttrium raises concerns about its long-term supply. Therefore, there is a need for efficient techniques to recover yttrium from secondary materials to ensure a stable supply. While the wastes contain only trace amounts of yttrium and often have complex elemental compositions, they are more readily available than primary sources. The yttrium content ranges from a few percent in spent phosphors to several hundred ppm in red mud, around a few dozen ppm in phosphogypsum, and up to several ppm in coal and coal fly ashes. Although conventional hydrometallurgical methods are commonly used, they lack selectivity for yttrium recovery. In contrast, unconventional solvometallurgical and bioleaching approaches currently play a relatively minor role in recovery applications. This review discusses a range of methods investigated for yttrium recovery from different types of secondary resources, including pretreatment (where applicable), leaching, and subsequent yttrium recovery from the resulting leachates. Although the chemical and phase compositions of yttrium-bearing waste materials differ substantially, necessitating tailored treatment strategies, acid leaching remains the predominant extraction route and is most commonly followed by solvent extraction and/or oxalate precipitation. Most studies reported to date have been conducted at the laboratory scale. Despite progress and the development of promising recovery concepts, the efficient separation of high-purity yttrium from other rare earth elements and co-existing impurities continues to represent the key obstacle to commercial-scale application.

YBO3:Eu3+ phosphors are regarded as strong candidates for high-performance luminescent materials owing to their excellent luminescence efficiency. In this study, novel YBO3:Eu3+ porous/hollow microspheres were synthesized via a simple, continuous ultrasonic spray pyrolysis (USP) process using different organic additives. XRD analysis confirms that all samples crystallize in a pure hexagonal YBO3 phase, indicating that the additives do not affect phase formation. Electron microscopy reveals a clear morphological evolution from solid to porous and hollow microspheres, with tunable shell thickness and cavity size. Compared with solid microspheres, the obtained hollow microspheres significantly reduce the consumption of rare earth materials with minimal influence on luminescence properties. The results suggest that hollow microspheres are promising substitutes for solid microspheres in the field of rare earth phosphors and the ultrasonic spray pyrolysis (USP) approach shows great potential in large-scale synthesis of morphology-controllable microspheres.

Rare earth phosphors are core materials for white LEDs (WLEDs), enabling color conversion. However, traditional types suffer from poor optical tunability and difficult processing. Polymer-bonded variants overcome these limitations, offering high fluorescence efficiency, stability, and dispersibility, combining polymer flexibility with rare earth traits. This review covers coordination groups, luminescent colors, and functional features of bonded polymers, analyzing different groups' effects on performance. It summarizes polymer-induced functional enhancements and discusses development prospects.

NaLa(MoO4)2 (NLM): Er[3+], Nd[3+] phosphors were successfully synthesized by a high-temperature solid-state reaction method, and their phase structure, electronic structure, and near-infrared luminescence properties were systematically investigated. XRD, SEM, and EDS analyses indicate that Er[3+] and Nd[3+] ions were effectively incorporated into the NLM host lattice while maintaining a well-defined single-phase structure. Combined with Rietveld refinement and first-principles calculations, the lattice variation, band structure, and density of states of the co-doped system were analyzed. The results reveal that the introduction of rare-earth ions generates localized 4f electronic states near the Fermi level and reduces the band gap, which is favorable for electronic transitions and energy-transfer processes.Based on absorption spectra and Judd-Ofelt theory, the intensity parameters, oscillator strengths, radiative transition probabilities, as well as the absorption and emission cross-sections of Nd[3+] ions were evaluated. Under 808 nm excitation, the co-doped samples exhibit enhanced 1064 nm near-infrared emission, indicating that Er[3+] ions can effectively act as sensitizers to promote the luminescence of Nd[3+] ions. Furthermore, the variations in fluorescence lifetimes at 1550 nm and 1064 nm, together with the calculated energy-transfer efficiency, further confirm the occurrence of the Er[3+] → Nd[3+] energy-transfer process. In addition, the upconversion emission of Er[3+] under 980 nm excitation is significantly suppressed after Nd[3+] incorporation. Combined with the excitation power-dependent luminescence behavior in the range of 157-507 mW, the upconversion process is identified as a two-photon mechanism.The calculated elastic constants and related mechanical parameters demonstrate that the co-doped NLM system possesses good structural stability and moderate lattice flexibility. Such a stable local crystal-field environment is beneficial for suppressing non-radiative relaxation losses and maintaining efficient near-infrared luminescence and energy transfer. Overall, the obtained results suggest that NLM: Er[3+], Nd[3+] phosphors have promising potential for near-infrared luminescence applications.

Near infrared (NIR) emitting, Nd[3+]-doped Rankinite type Ca3Si2O7 silicate phosphors were synthesized using solid-state reaction method. Morphology, crystal structure and optoelectronic properties of the proposed silicate were analysed using SEM, XRD and photoluminescence, respectively. XRD confirms the Rankinite type monoclinic structure having a space group of P21/a (No.14). SEM, EDS and elemental mapping studies approve the surface properties and elemental composition. The photoluminescence (PL) emission observed in NIR region upon Nd[3+] doping at 1065 nm attributed to [4]F3/2 → [4]I11/2 under the fixed excitation of 589 nm ([4]I9/2 → [4]G7/2). The concentration quenching is recorded at 1.0 mol% of Nd[3+] ions. The critical distance (Rc) is 31.39 Å, which surpasses the ideal range ~5 Å, typical of exchange interactions. Van Uitert confirmed the transfer of energy between nearest neighbouring ions, which contributes to the concentration quenching. The obtained results suggest it as a potential optical material for optoelectronic devices.

Undoped and Eu2+/Mn2+-doped strontium pyrophosphate phosphors (α-Sr2P2O7 and α-Sr1.84P2O7:0.04Eu2+/0.12Mn2+) were successfully prepared using a homogenous co-precipitation approach for detailed EPR-PL and crystal-field effects analysis. XRD confirmed that both samples crystallized in a single-phase orthorhombic structure, indicating long-range phase purity and the seamless integration of dopants into the host lattice without structural degradation. To investigate the subtle, localized structural distortions induced by the dopants, EPR spectroscopy was employed as a highly sensitive primary probe. The room temperature EPR spectrum revealed broad Mn2+ resonance lines and distinct low-field resonances for Eu2+, highlighting enhanced crystal-field interactions arising from the relatively low local symmetry at the substituted Sr2+ sites. Under UV excitation, the doped phosphor shows two sharp bands centered at 425 nm (blue) and 560 nm (yellow). Eu2+ acts as a sensitizer for Mn2+ in the phosphor lattice, thereby suggesting a potential energy transfer mechanism from Eu2+ to Mn2+. This opens a channel to tune the luminescence for possible white light generation through future concentration optimization and decay kinetics studies. These phosphors, with their luminescence and structural characteristics, have potential for color tunable white light-emitting diodes (w-LEDs) and other solid-state lighting applications.

Rare-earth-doped transparent ceramics, as novel luminescent materials, show broad application prospects in the field of advanced photonics. In this study, a series of Gd2Hf2O7:Yb[3+],Er[3+] transparent ceramics were prepared by controlling Yb[3+] concentration via vacuum sintering. These ceramics exhibit a dense microstructure that effectively suppresses light scattering and nonradiative relaxation, enabling simultaneous visible light, near-infrared emission, and upconversion luminescence within a single ceramic system. The dual-mode emissions are attributed to the strong near-infrared absorption of Yb[3+] ions, as well as the efficient Yb[3+] → Er[3+] energy transfer under 980 nm excitation and the presence of Er[3+] → Yb[3+] energy transfer under ultraviolet light. Furthermore, these ceramics exhibit superior environmental resilience and hydrophobic properties. Accelerated hydrothermal aging tests reveal negligible phase decomposition, minimal decay in near-infrared and upconversion luminescence, and significantly enhanced performance compared to commercial aluminate phosphors. This property stems from the inherent chemical stability and dense structure of the ceramics. Gd2Hf2O7-based dense transparent ceramics, characterized by dual-mode luminescence, high transmittance, and exceptional durability, hold promise in addressing the stability limitations and integration challenges in harsh environments and high-power optoelectronic devices.

Novel MgSrB2O5:Eu3+ nanophosphor was synthesized by a simple, low-cost solution combustion method using urea as fuel. X-ray diffraction confirmed the formation of the phosphor with an average particle size of 28.63 nm. The MgSrB2O5:1.5 mol% Eu3+ sample shows a band gap of 4.79 eV and a refractive index of 2.0325. SEM images show an agglomerated arrangement of particles. For photoluminescence (PL) characterization, excitation wavelengths at 393 and 464 nm, emission peaks were obtained at 594, 616, 654 and 701 nm. The maximum PL intensity was observed at 1.5 mol% Eu3+ concentration. At 1.5 mol% (616 nm) concentration, quenching occurs mainly due to dipole-dipole interactions. These emissions are attributed due to the 5D0 → 7Fj = 1.2,3,4 transition of Eu3+, which varies with temperature. The average fluorescence lifetime of the Eu3+-doped MgSrB2O5 phosphor (1.5 mol%) was 2.6459 ms. The thermoluminescence (TL) behaviour of Eu3+-activated MgSrB2O5 was examined across a range of beta irradiation doses from 3 to 10 Gy. The resulting sample exhibited improved thermal stability. The emission at 701 nm falls within the far-red absorption spectrum of phytochrome, making it potentially useful for white light-emitting diode fabrication and beta radiation dosimetry.

Using BiOF as the main component of the phosphor, a series of BiOF phosphors doped with Tm[3+] and co-doped with Dy[3+] were synthesized by the high-temperature solid-state method. The phase structure and luminescence properties of phosphors were analyzed by XRD diffraction, fluorescence spectroscopy and ultraviolet near-infrared spectroscopy analysis system. The structure of the synthesized phosphor crystal is PbFCl, the symmetry is D4h, the space group is P4/nmm, and it belongs to the tetragonal crystal system. BiOF:Tm[3+] phosphor exhibits blue light emission, and the luminescent color of the phosphor can be changed to white light by co-doping Dy[3+] ions. When the Dy[3+] doping amount is 0.07, the color coordinates of Bi0.90OF:0.03Tm[3+], 0.07Dy[3+] phosphor are (0.3180, 0.3128), which is closest to the ideal coordinates of white light (0.33, 0.33). The study on the luminescence mechanism and fluorescence lifetime of Bi0.90OF:0.03Tm[3+], 0.07Dy[3+] shows that there is energy transfer between Tm[3+] and Dy[3+].The dipole-dipole interaction contributed to energy transfer from Tm[3+] to Dy[3+] ions. The results indicate that BiOF:Tm[3+], Dy[3+] phosphors are promising candidates for near-ultraviolet white LED emitting phosphors.

Alkali metal rare earth double tungstates AM(WO4)2 (A = alkali metal; M = trivalent metal cation) are an extensively researched class of materials with applications not only as phosphors but also in photonics and biomedicine. However, the structural, optical and thermal properties of these materials are yet to be investigated. The crystal structures of the double tungstates are elucidated and the role of the Bi3+ lone pair activity of ABi(WO4)2 (A = Li, Na, K) is discussed. Furthermore, the optical properties of AM(WO4)2 are studied using UV-vis and luminescence spectroscopy. The bismuth compounds KBi(WO4)2 and NaBi(WO4)2 revealed s-p fluorescence from the trivalent bismuth cations, while the other compounds dependent on the trivalent cation M show either broad ligand to metal charge transfer transitions or typical f-f transitions from the rare earth cations. For most of the compounds, the energy transfer from the tungstate moieties towards the rare earth elements was successful, verifying an effective antenna. The luminescence behaviour of the polymorphs LiLa1-xPrx(WO4)2 shows different intensities of the respective f-f transitions of Pr3+ with respect to the doping concentration, especially when excited at the charge transfer transition of the tungstate units. Furthermore, the thermal properties of the double tungstates were investigated by elucidating the phase transition temperatures for those polymorphs exhibiting two temperature phases. For LiM(WO4)2 (M = La, Ce, Pr, Nd), the phase transition temperature revealed a trend for different sized rare earth elements from the low- to the high-temperature polymorphs. Moreover, MAPLE calculations were carried out for those double tungstates with single crystal data reported for the first time.

Luminescent rare-earth oxide phosphors are of considerable interest for advanced lighting, anticounterfeiting, security applications, dosimetry, etc. because of their unique performance of sharp and distinct emission peaks, spectral tunability, long luminescence decay times, exceptional thermal stability, etc. In this work, the Eu[3+]-activated La2Zr2O7 (LZO) nanophosphors having a defect fluorite structure were synthesized by the nitrate-citrate gel combustion method, and the influence of monovalent alkali-ion co-doping (Li[+]/Na[+]/K[+]) on their defect chemistry and luminescence behavior was systematically studied. Among them, Li[+] co-doped nanophosphor (La1.72Eu0.22Li0.06Zr2O7) showed a 1.5-fold increase in the PL emission intensity with better CIE chromaticity coordinates (0.6394, 0.3598), a higher correlated color temperature value (1973 K), and excellent color purity (89%), overcoming the shortcomings in the red component of LEDs. X-ray photoelectron spectroscopy analysis indicated oxygen vacancy-related defect centers in Li[+] ion co-doped phosphor materials. Judd-Ofelt (J-O) analysis studied the increased asymmetric environment around the activator ion, Eu[3+], upon co-doping. Furthermore, La1.72Eu0.22Li0.06Zr2O7 nanophosphor demonstrated latent fingerprint detection as well as dosimetry applications via gamma radiation. Hence, this Li[+] co-doped Eu[3+]: LZO nanophosphor can be a plausible option for the red component in lasers, display devices, and solid-state lighting, latent fingerprint analysis, and dosimetry studies.

The article investigates optical properties of Ca0.5MgAl3O6: Eu3+, Dy3+, and Tb3+ (x = 0.5, 0.7, 1.0, 1.3, and 1.5 mol%) novel phosphors synthesized by the simple combustion method. The XRD spectra were matched successfully with the standard JCPDS database file no. 9002506, and refinement data confirm the hexagonal phase of the Ca0.5MgAl3O6 matrix. Under near-ultraviolet light excitation, the Eu3+-doped phosphor shows emission peaks at 593 and 618 nm, whereas the Dy3+-doped Ca0.5MgAl3O6 phosphor shows the emission peaks at 486 and 547 nm. In the case of Tb3+ ions, the emission peak is at 491 and 546 nm. The concentration quenching phenomenon was observed at x = 1.0 mol%. The structural properties were investigated using characterization techniques such as the Rietveld refinement, FTIR, and UV-visible spectroscopy. The morphology was determined using the FE-SEM, and the elemental composition was verified using the EDS. The average particle size determined using the ImageJ software is 52.46 nm. The CIE chromaticity diagram confirms the multicolor light emission characteristics of the Ca0.5MgAl3O6 matrix, and it has good caliber for use as RGB phosphor and solid-state lighting applications.