Comprehensive Review on Downconversion/Downshifting Silicate-Based Phosphors for Solar Cell Applications

Insufficient utilization of the solar spectrum in commonly employed solar cells, stemming from a spectral mismatch between the solar spectrum and the solar cell's band gap, poses a barrier to enhancing solar cell efficiency. To overcome this challenge, downconverting silicate phosphors are employed in solar cells to capture the infrared spectrum of sunlight, thereby augmenting solar cell efficiency. Downconversion/downshifting involves in converting high-energy photons into one or two near-infrared (NIR) photons. Remarkably, silicate-based downconverting phosphors enhance solar cell sensitization, light scattering, antireflectivity, and stability. This review delves into the various energy transfer mechanisms utilized in silicate phosphors. The key aspects covered in this review encompass the development of silicate phosphors that emit NIR light and their synthesis process. The working principle of the solar cell and its parameters are discussed. The impacts of silicate phosphor size, coverage, volume concentration, and arrangement on solar cell performance are also explored. Furthermore, the study addresses several intriguing approaches for developing innovative silicate phosphors to enhance solar cell performance.

Energy transfer for Ce3+ → Tb3+ → Sm3+ induced bright white emission in single-phase CaLa4(SiO4)3O:Ce3+, Tb3+, Sm3+ phosphors and their application in white-light-emitting diodes

The emergence of phosphor-converted white-light-emitting diodes has crucial significance in the sustainable development of energy; hence, the evolution of phosphors with eminent luminescence and high stability is imperative. In this study, a tri-doped system composed of rare earth ions Ce3+, Tb3+, and Sm3+ incorporated into a CaLa4(SiO4)3O host is reported, and the energy transfer, tunable single-phase white emission, and favorable thermostability of the Ce3+-Tb3+-Sm3+ system were explored. Rietveld refinement results coincided with the original model of the crystal structure, and a band gap energy of 4.612 eV calculated using density functional theory (DFT) demonstrated the system as an appropriate luminescent host with a wide energy gap. Furthermore, ET processes for Ce3+ → Tb3+, Tb3+ → Sm3+, and Ce3+ → Tb3+ → Sm3+ were investigated via steady-state photoluminescence and decay measurements. Besides, the activation energies of CLSO:3%Ce3+, 9%Tb3+, y%Sm3+ (y = 7, 9) were 0.205 eV and 0.223 eV, respectively, showing outstanding thermal quenching resistance. Devices made with LED beads containing CLSO:3%Ce3+, 9%Tb3+, y%Sm3+ (y = 7, 9) phosphors exhibited bright white light with CCT ≈ 3586 and 3307 K and Ra ≈ 81.0 and 78.5, respectively. This study demonstrates that energy transfer for Ce3+-Tb3+-Sm3+ in a tri-doped system offers an interesting design prospect for promoting single-phase white emission phosphors.

Spectrally tunable near-infrared photoluminescence in MP3O9:Cr3+ (M = Al, Ga, In) phosphate phosphors

Modulation of the octahedral crystal field environment of Cr3+ is an effective approach to achieve tunable emission. Here, we prepared a series of broadband MP3O9:Cr3+ (M = Al, Ga, In) near-infrared (NIR) phosphors, and cubic AlP3O9:Cr3+ (APO-c:Cr3+) and monoclinic AlP3O9:Cr3+ (APO-m:Cr3+) phosphors were prepared by controlling the synthesis temperature. The emission wavelength was tuned from 787 nm for APO-c:Cr3+ to 894 nm for monoclinic InP3O9:Cr3+ (IPO:Cr3+) by regulating the M ion and reducing the crystal field intensity. Excitingly, the MP3O9:Cr3+ (M = Al, Ga, In) family shows excellent thermal stability; the emission intensity of APO-c:Cr3+, APO-m:Cr3+ and monoclinic GaP3O9:Cr3+ (GPO:Cr3+) can still maintain 95.6%, 86% and 86% of that at room temperature when heating to 423 K, respectively. An NIR LED device was prepared by incorporating GPO:Cr3+ and a blue light LED, demonstrating the potential application in night vision and non-destructive testing.

Broadband La2LiSbO6: Cr3+ Phosphors with Double Luminescent Centers for NIR pc-LEDs

The La2LiSbO6: xCr3+ phosphors were synthesized by means of a high-temperature solid-phase method. Based on the differences in ionic radius, valence state, and formation energy, the substitution sites of Cr3+ ions are discussed in detail. The optimized doping concentration of Cr3+ is determined to be 0.01. Under 517 nm excitation, the La2LiSbO6: 0.01Cr3+ phosphor presents a wide emission band (from 700 to 1350 nm) with a peak centered at 952 nm. Additionally, its corresponding full width at half-maximum is 155 nm, and the internal quantum efficiency reaches 62.4%. Meanwhile, the emission intensity of the La2LiSbO6: 0.01Cr3+ phosphor at 373 K is about 63.7% of that at room temperature, exhibiting good thermal stability. Aiming to fabricate a near-infrared phosphor-converted light-emitting diode device, the La2LiSbO6: 0.01Cr3+ phosphor is mixed with epoxy adhesive and cured on a green light-emitting diode chip. Under the irradiation of the fabricated light-emitting diode device, fruits and writing in the dark environment can be captured by a near-infrared camera. Hence, the La2LiSbO6: 0.01Cr3+ phosphor is promising for night vision.

Achieving Broadband NIR-I to NIR-II Emission in an All-Inorganic Halide Double-Perovskite Cs2NaYCl6:Cr3+ Phosphor for Night Vision Imaging

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) offer numerous advantages, including compact size, tunable emission spectra, energy efficiency, and high integration potential. These features make them highly promising for various applications, such as night vision monitoring, food safety inspection, biomedical imaging, and theragnostics. All-inorganic halide double-perovskite materials, known for their large absorption cross section, excellent defect tolerance, and long carrier diffusion radius, serve as unique matrices for constructing near-infrared fluorescent materials. In this study, we successfully prepared the all-inorganic metal halide double-perovskite Cs2NaYCl6:Cr3+ using a grinding-sintering method. A small fraction of the [YCl6] octahedra within the host material's lattice was substituted with Cr3+ ions, resulting in the creation of the Cs2NaYCl6:Cr3+ phosphor. When excited with λ = 310 nm UV light, the phosphor exhibited a broad emission range spanning from 800 to 1400 nm, covering the NIR-I and NIR-II regions. It had a broad bandwidth emission of 185 nm and achieved a fluorescence quantum yield of 20.2%. The unique broadband emission of the phosphor originates from the weak crystal field environment provided by the Cs2NaYCl6 host matrix, which enhances the luminescence properties of the Cr3+ ions. To create NIR pc-LEDs, the phosphor was encapsulated onto a commercially available UV LED chip operating at 310 nm. The potential application of these NIR pc-LEDs in night vision imaging was successfully validated.

Site-Selective Occupancy Control of Cr Ions toward Ultrabroad-Band Infrared Luminescence with a Spectral Width up to 419 nm

Infrared-emitting phosphor-converted light-emitting diodes (LEDs) are desirable light sources for a very wide range of applications such as spectroscopy analysis, nondestructive monitoring, covert information identification, and night-vision surveillance. The most important aspect of infrared emitters for spectroscopy is to cover the widest possible wavelength range of emitted light. However, developing ultrabroad-band infrared emitters based on converter technology is still a challenging task due to the lack of suitable phosphor materials that emit in a wide wavelength range upon excitation from blue-emitting chips. Herein, this work demonstrates Cr³⁺-activated Mg₂SiO₄ infrared phosphors with a super wide infrared spectral range of 600 to 1400 nm and high internal quantum yield up to 80.4% upon 460 nm excitation. Site-selective occupancy of Cr³⁺ emitters in two different Mg sites in the Mg₂SiO₄ lattice results in two distinct broad emission bands peaking at 760 and 970 nm, both of which contribute to the ultrabroad-band infrared luminescence with a full width at half maximum (FWHM) of 419 nm. This is by far the broadest infrared emission to the best of our knowledge. On this basis, an ultrabroad-band infrared LED prototype has been fabricated by the combination of the Mg₂SiO₄:Cr³⁺ phosphor with a blue LED chip, which shows great potential for imaging and sensing applications. This work demonstrates that site-selective occupancy control of Cr ions is an effective strategy for developing ultrabroad-band Cr³⁺-doped phosphors.

Cr3+-doped InTaO4 phosphor for multi-mode temperature sensing with high sensitivity in physiological temperature range

With the increasing demand for non-contact temperature sensing, the development of optical thermometer with excellent performance is more and more compelling. Cr3+-doped InTaO4 phosphor was prepared for the implementation of...