Active Ion Concentration Research Articles

Analysis of luminescent properties of 40PbO–35Bi2O3–25Ga2O3 glasses doped with Er2O3

The Er3+ doped lead–bismuth–gallium oxide glasses were prepared by melt quenching technique. The spectral and luminescent properties were analyzed based on experimental and theoretical calculations. Analysis of Er3+ concentration dependences of density and electronic optical polarizability was carried out. The radiative lifetime values for 4S3/2 and 4F9/2 energy states were calculated using Judd-Ofelt theory. In the glassy system under study, the concentration quenching of state 4S3/2 was discovered at content of erbium ions above 0.869 × 1020 cm−3. It was also shown that 4F9/2 energy state was isolated from concentration effects and showed an increase in luminescence intensity with increasing concentration of activator ions. The luminescence quantum efficiency for transition 4S3/2 → 4I15/2 was about 40%, which allows us to consider this system as a glassy matrix effective for activation by rare-earth ions.

Spectral studies of thermally stable Dy3+/Sm3+ co-doped Li2Ba5W3O15 phosphors for warm white LEDs

In the current study, a series of Li2Ba5W3O15: RE3+ (RE = Dy, Sm) [LBW:Dy3+/Sm3+] phosphors were prepared using a high-temperature solid-state method. X-ray diffraction, Scanning electron microscopy with energy-dispersive x-ray analysis scans showed that the crystal form was consistent with the standard LBW and comprised small irregularly shaped particles. Diffuse reflectance spectral (DRS) data was utilized to calculate the band gaps. Fluorescence study shows that LBW material doped with Dy3+ and Sm3+ yield distinct colors at 496 nm (blue) for Dy3+ and 582 nm (green-yellow), 612 nm (yellow), and 669 nm (red) for Sm3+ when excited by near-ultraviolet (336 nm) light. The observation of energy transfer between Dy3+ and Sm3+ ions play a role in modifying the luminescence of LBW:Dy3+/Sm3+ co-doped phosphors. With a constant excitation wavelength (λ Ex), different levels of activator doping lead to a change in the emission colors from their neutral white light to a deep orange-red region for LBW:Dy3+/Sm3+ phosphors. The decay curves demonstrate a decrease in lifetime with an increase in the concentration of activator ions (Sm3+). For D3S5 phosphor, the temperature-dependent photoluminescence characteristics were analyzed under λ Ex = 336 nm excitation. The results indicate excellent luminescence thermal stability with an activation energy of 0.16 eV at λ Ex = 336 nm. With its low color-correlated temperature and good thermal stability, the prepared phosphor sample shows potential as a solid-state emitting phosphor that can be used with UV chip stimulation for warm white LED applications.

Color tunable upconversion luminescence from ex-situ sol-gel derived Titania-Silicate dense glass-ceramic co-doped with Pr3+-Yb3+ ion pair

Praseodymium–Ytterbium (Pr3+-Yb3+) ion pair co-doped with Silica-Titania dense glass ceramic material was synthesized by novel ex-situ sol-gel method after annealing at ca. 900 °C and investigated for their morphological, structural and luminescence characteristics. Color-tunable upconversion luminescence (UCL) are observed from varying Yb3+ (X mol%; X = 0.0, 0.7, 1.5, 3.0) and fixed Pr3+ (0.7 mol%) ions co-doped ex-situ sol-gel silicate-titania (STPYX) dense glass-ceramic (DGC) materials under 980 nm laser diode pumping source due to the transfer of energy from the Yb3+→ Pr3+ ion. An original ultra-broadband UCL spectra is achieved from the STPYX-DGC materials for excitation photon of wavelength (λex = 980 nm) for varying Yb3+ ion concentration, where the optimized UCL has been observed for material with 1.5 mol% Yb3+ ion concentration. Further, two dimensional spatially resolved photoluminescence intensity distribution study has also been performed using 2D-PL confocal mapping throughout the STPY15-DGC material for a similar excitation source. The color tunability from white to red is evident from the CIE co-ordinate of corresponding UCL spectra of the as-synthesized materials at different activator (Yb3+) ion concentrations. An intense absorption spectrum with peaks assigned to both Pr3+ and Yb3+ ions is also observed for the STPY07-DGC material.

Electrochemical Properties and Performance of Supersaturated Vanadium (IV) and V(V) Electrolytes

Earlier research has shown that supersaturated vanadium sulfate electrolytes can remain stable for an extended time ranging from hours to days making them suitable for electrochemical energy storage applications. This study investigates the electrochemical characteristics of supersaturated vanadium IV and V sulfate solutions and the solvation structures of molecules in these solutions. The electrochemical characterizations, e.g., OCV, constant current/voltage/overpotential oxidation, and reduction, reveal that supersaturated V(IV) and V(V) solutions contain electrochemically active ions, inactive-but-convertible molecules, and inactive-and-unconvertible molecules. The chemical conversion rate from inactive-but-convertible molecules to active ions is high enough to maintain a constant active ions concentration during the electrochemical reactions. Possible structures and the relationship of these structures to their electrochemical activity at supersaturated levels were discussed. The inactive-but-convertible molecules are suggested to be the agglomerates of the individual dissociated vanadium ion pairs, while the inactive-and-unconvertible molecules consist of undissociated vanadium salt molecules with the sulfate anions bonded directly to the vanadium cations. This work also found that preparation methods (with or without preheating the electrolyte during synthesis) and the oversaturation level can affect the composition of the molecules in the electrolyte.

1.76 μm on-chip gain characteristics of Tm3+ in a rib waveguide based on Tm3+-doped LiNbO3 thin-film on insulator

A theoretical study has been performed on 1.76 μm on-chip amplification characteristics of Tm3+ in a rib waveguide of LiNbO3 on insulator (Tm:LNOI) under 795 nm wavelength pumping. Steady-state rate equations and propagation equations of signal and pump waves are established on the basis of a three-level model of Tm3+ system with the cross relaxation process 3H4→3F4: 3H6→3F4 included. The validity of the three-level model is demonstrated by referencing previously reported experiment result of Er3+-doped LNOI waveguide amplifier and by examining the effect of Tm3+ blue upconversion emissions on the 1.76 μm amplification. Besides the relations of signal gain to propagation length, launched pump power and input signal power, the effects of waveguide cross-section geometry and Tm3+ concentration on the gain characteristics are also studied. The results show that the waveguide cross-section geometry affects definitely the gain performance via its effect on mode field. The Tm3+ concentration affects the signal gain also via its effect on the 3H4→3F4: 3H6→3F4 cross relaxation coefficient, besides the conventional effect that higher active ion concentration yields larger signal gain. A comparison with conventional Ti4+(Zn2+)-diffused Tm3+-doped LN [Ti(Zn):Tm:LN] waveguide shows that the Tm:LNOI waveguide has much better gain performance than the Ti(Zn):Tm:LN waveguide, including much stronger pump power and propagation distance dependences of signal gain, much higher signal gain and much lower threshold pump power. These features are associated with significantly increased Tm3+ population inversion extent due to ultra-compact mode field and larger overlapping factor of mode field and Tm3+ population profiles in the Tm:LNOI waveguide.

Management of plant nutrient dynamics under alkaline soils through graded application of pressmud and gypsum.

An incubation experiment was conducted to monitor the effect of different organic matter inputs with the graded application of gypsum at different time intervals on soil pH, sodium (Na) content and available plant nutrients like nitrogen (N) and sulphur (S) in alkaline soil. The experiment was formulated with nine treatments, i.e. control (T1), recommended dose of fertilizer (RDF) (T2), RDF+Gyp1 (T3), RDF+FYM5+Gyp2 (T4), RDF+FYM10+Gyp1 (T5), RDF+PM5+Gyp2 (T6), RDF+PM10+Gyp1 (T7), RDF+FYM2.5+PM2.5+Gyp2 (T8), RDF+FYM5+PM5+Gyp1 (T9) with three replications. Periodical soil samples were taken at six and twelve months intervals. Results showed that the addition of organic matter reduced the pH and Na content in the soil. More reduction was observed at one year period as compared to six months. The addition of farmyard manure (FYM) and pressmud (PM) at 10 t/ha with gypsum (1 t/ha) improved available N and available S content as compared to organic inputs (5 t/ha) with gypsum (2 t/ha) in soil. Pressmud application with FYM showed better availability of plant nutrients and a reduction of soil pH (8.39 to 7.79) and Na content from 626 to 391 mEq/L in the soil during the incubation period. During the study, the application of treatment T9 (FYM and PM in equal ratio with 1 t/ha gypsum) showed a better availability of available N (175 to 235 kg/ha) and S (15.44 to 23.24 kg/ha) and reduced the active ion concentration of Na. This study is very useful for the management of sodium toxicity, improving soil health and the mineralization rate of organic matter through the application of organic inputs for sustainable crop production.

Orange-red luminescence of samarium-doped bismuth-germanium-borate glass for light-emitting devices.

Samarium (Sm3+ )-doped glass has sparked a rising interest in demonstrating a noticeable emission in the range of 400-700, which is advantageous in solid-state lasers in the visible region, colour displays, undersea communication, and optical memory devices. This study reports the fabrication of Sm3+ -doped bismuth-germanium-borate glasses were established using a standard melt-quenching technique and inspection by absorption, steady-state luminescence, and transient studies. The typical peaks of Sm3+ ions were detected in the visible range under 403 nm excitation. A strong emission band was detected at 599 nm that resembles the 4 G5/2 →6 H7/2 transition of Sm3+ ions for BGBiNYSm0.5 glass. Furthermore, a reddish-orange (coral) luminescence at 646 nm that resembles the 4 G5/2 →6 H9/2 transition was also perceived. The stimulated emission cross-section of 4 G5/2 level for BGBiNYSm0.5 glass was 0.39 × 10-22 cm2 . Lifetime of the 4 G5/2 level was enhanced for the BGBiNYSm0.5 glass and decreased with an increase in active ion concentrations. The lifetime quenching of ions at the metastable state was because of energy transfer among Sm3+ ions by cross-relaxation channels. Commission Internationale de l'Éclairage (CIE) coordinates were evaluated from the emission spectra. Moreover, all the findings recommend these glass as light-emitting materials in the coral region at 599 nm for solid-state lighting applications.

Enhanced Yb:YAG Active Mirrors for High Power Laser Amplifiers

The work is aimed at the investigation of the influence of nonlinear active ions concentration profiles in Yb:YAG laser elements on temperature distribution and wavefront distortions during amplification using sub-kilowatt level diode pumping. A mathematical model is presented for the theoretical study of the amplification process in crystals with cubic crystal system. A detailed comparison of Yb:YAG active elements with the same thickness and absorbed pumping power, but with various concentration profiles of Yb3+, ions is carried out. It is shown that the use of active elements with an increasing dopant concentration in the pump beam direction allows one to optimize the temperature profile inside the active element and, thus, reduce the thermal-induced wavefront distortions of the amplified radiation. Modeling is carried out for the experimentally grown crystal with linear concentration gradient profile. It is shown that the linear doping profile with a gradient of 0.65 at.%/mm allows increasing the small-signal gain up to 10% and decreasing the thermal-induced wavefront distortions by ~15%.

Luminescence of undoped and Eu3+ activated zinc gallate phosphor: Synthesis, unusual intense 5D0 → 7F4 red emission

A series of Eu3+-doped ZnGa2O4 samples were synthesized via the urea-glycine combustion route. Powder X-ray diffraction (XRD) was used to investigate the crystallinity of the samples, energy dispersive spectroscopy (EDS) to explore the elemental composition, Fourier transform infrared (FTIR), to observe the vibrational modes of the samples, photoluminescence (PL) to determine the luminescence properties. The XRD data prove that the samples remain single cubic structure even at high concentrations of Eu³⁺, enabling the formation of a unique emission spectrum. The active ion concentration was varied to examine the influence of concentration on luminescent properties. This study revealed a 5D0 →7F4 transition located at 700 nm with unusual intensity that has not been documented in the literature, which suggests that the active ion concentration can influence the luminescent characteristics of the phosphors. The increasing Eu3+ content increases the number of Eu3+ ions in ZnGa2O4 host lattice, which enhances the luminescence efficiency of the phosphor. However, beyond a certain level of Eu3+content (i.e., 3 wt% Eu3+), the number of Eu3+ ions becomes excessive, resulting in a reduction in luminescence efficiency due to concentration quenching. The dipole dipole interaction is elucidated to play a prominent role in the mechanism of Eu3+ quenching in the ZnGa2O4. An assessment of color coordinates based on emission spectra reveals that the coordinates shift from blue to the white light region, and then to red as Eu3+ content increases. This suggests that there is a substantial relationship between the Eu3+ concentration and the measured color coordinates.

Highly Reliable Electrochemical Metallization Threshold Switch Through Conductive Filament Engineering Using Two‐Dimensional PtSe2 Insertion Layer

AbstractElectrochemical metallization threshold switch (ECM TS) has received significant attention for various applications owing to its high ON/OFF ratio, fast switching characteristics, and simple active electrode/dielectric layer/inert electrode structures. However, the excess diffusion of active metal ions causes severe variation in threshold voltage and poor endurance. Furthermore, the small room for inert electrode metal is a problem to be solved for various applications of ECM TS. Here, a novel structure is proposed in which a two‐dimensional platinum diselenide (PtSe2) is inserted between the dielectric layer and inert electrode to engineer the conductive filament by controlling the active metal ion concentration. The low work function, superior inertness, layered structure, and smooth surface of PtSe2 insertion layer lead to thin and weak conductive filament with few active metal atoms and allow the use of various metals as inert electrode. Consequently, PtSe2‐inserted ECM TS shows high reliability in both threshold voltage distribution (σ/µ = ≈6.58%) and endurance (>106 cycles). Furthermore, PtSe2‐inserted ECM TS‐based 2 × 2 cross‐bar array is proposed as AND and OR logic circuits. This study is expected to pave the way for the development of ECM TS for next‐generation electronic applications.

Design Optimization of 12-Core Amplifier Based on Erbium Ytterbium Co-Doped Fiber for Spatial Multiplexed Transmission System

A 20 dB gain 12 cores Er <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3+}$</tex-math></inline-formula> /Yb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3+}$</tex-math></inline-formula> co-doped cladding pumped amplifier in C-band with only 5.3 W of pump power has been achieved. A classical rate equation model has been applied for the amplifier design. Parameters such as active fiber length, pump power and ions concentration have been investigated and optimized. Results obtained through numerical simulation and experimental investigations are compared. Different use cases of MC-EYDFA have been studied, such as various transmission configuration or multi-core amplifier in ROADM architectures. 1200-km with 200G DP-QPSK and 300 km with 400G DP-16QAM are achieved in serial configuration at 1550 nm. This is a first step towards SDM transmission using power efficient amplifiers, for cost, energy and footprint saving.

Photoluminescence of Ca0.5Ba0.5Ga2S4:Сe3+, Sm3+ solid solutions over a wide range of temperatures and excitation levels

Сa0.5Ва0.5Ga2S4 solid solutions activated by Ce3+ and Sm3+ ions have been synthesized by solid state reaction and photoluminescence (PL) properties are investigated. PL emission and PL excitation spectra of thiogallates with different concentration of activator ions have been measured. Temperature quenching of PL emission of Ca0.5Ba0.5Ga2S4:Ce3+, Sm3+ solid solutions over wide temperature ranges (10–300 K) are investigated. The influence of optical excitation intensity on position stability and shapes of radiation spectra, as well as the emission efficiency of micropowders under investigation within the range of pulsed laser excitation levels from 10 to 2.2 × 105 W/cm2, has been established. PL decay kinetics of Ca0.5Ba0.5Ga2S4:Ce3+,Sm3+ solid solution micropowders at femtosecond laser excitation are studied in detail.

On the structures and luminescence properties of Eu3+ -doped Li2 CaGeO4 , Ca2 GeO4 , and Ca5 Ge3 O11 compounds.

Powder samples of Li2 CaGeO4 , Ca2 GeO4 , and Ca5 Ge3 O11 doped by 0.5, 1, 2, 3, 4 and 5 at% Eu3+ relative to the Ca2+ , were prepared using a conventional solid-state synthesis technique. X-ray diffraction (XRD) analyses confirmed obtaining the pure phases at all dopant concentrations. In parallel, single crystals of the three compounds with the experimentally found optimal Eu3+ concentration were grown using a flux method. Structural investigation on the single crystals were done with a special attention to the form of the Ca-O polyhedron, the mean Ca-O distance, the Ca-Ca distance in the structure, the distortion degree of the polyhedron, as well as the Eu-Ca substitution site. The main spectral characteristics were analyzed and several relationships between the structural and spectra features were found. The optimal dopant concentration was 3 at% for Ca2 GeO4 and 4at% for Ca5 Ge3 O11 and Li2 CaGeO4 . Commission Internationale de l'éclairage coordinates of the samples showed emission colours in the red region close to the standard red coordinates and slightly influenced by the active ion concentration. The obtained results showed that europium-doped Li2 CaGeO4 , Ca2 GeO4 , and Ca5 Ge3 O11 could be used as red phosphors.

Quantification of the Activator and Sensitizer Ion Distributions in NaYF4 :Yb3+ , Er3+ Upconverting Nanoparticles Via Depth-Profiling with Tender X-Ray Photoemission.

The spatial distribution and concentration of lanthanide activator and sensitizer dopant ions are of key importance for the luminescence color and efficiency of upconverting nanoparticles (UCNPs). Quantifying dopant ion distributions and intermixing, and correlating them with synthesis methods require suitable analytical techniques. Here, X-ray photoelectron spectroscopy depth-profiling with tender X-rays (2000-6000eV), providing probe depths ideally matched to UCNP sizes, is used to measure the depth-dependent concentration ratios of Er3+ to Yb3+ , [Er3+ ]/[Yb3+ ], in three types of UCNPs prepared using different reagents and synthesis methods. This is combined with data simulations and inductively coupled plasma-optical emission spectroscopy (ICP-OES) measurements of the lanthanide ion concentrations to construct models of the UCNPs' dopant ion distributions. The UCNP sizes and architectures are chosen to demonstrate the potential of this approach. Core-only UCNPs synthesized with XCl3 ·6H2 O precursors (β-phase) exhibit a homogeneous distribution of lanthanide ions, but a slightly surface-enhanced [Er3+ ]/[Yb3+ ] is observed for UCNPs prepared with trifluroacetate precursors (α-phase). Examination of Yb-core@Er-shell UCNPs reveals a co-doped, intermixed region between the single-doped core and shell. The impact of these different dopant ion distributions on the UCNP's optical properties is discussed to highlight their importance for UCNP functionality and the design of efficient UCNPs.

Europium doped glasses from the oxide system CaO-GeO2-Li2O-B2O3 for LED application

Europium doped glasses with three different compositions and different dopant concentrations were prepared from the CaO-GeO2-Li2O-B2O3 system. The influences of Eu3+ ions concentration on the thermal stability of the glasses were investigated by DTA analyses. The IR spectra display variations in the glass structures depending on the glass composition and dopant concentration. The excitation and emission spectra of all glasses consist of characteristic peaks of Eu3+ ions. Some changes are observed with the variation of the glass composition and active ion concentration. Chromaticity coordinates of the examined glasses are placed in a relatively narrow area in the red part of the diagram. The obtained results show that europium doped glasses from the oxide system CaO-GeO2-Li2O-B2O3 can be used for red phosphors.

Effect of doping distribution on the lasing performance of a cerium-doped lithium calcium aluminum fluoride ultraviolet laser crystal

We report multi-photon luminescence and Laser Ablation–Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) as a non-destructive and sensitive method of visualizing the concentration and distribution of activator ions doped to a crystal host, respectively. Here, LA-ICPMS is able to detect concentrations that are less than 0.1%. Using these methods and a large 110-mm diameter Czochralski method-grown cerium-doped lithium calcium aluminum fluoride (Ce3+:LiCaAlF6 or Ce:LiCAF), we observed that Ce is distributed non-uniformly with varying concentrations across the diameter of the crystal boule. We further verify quantitatively that luminescence intensity increases in proportion to doping density. Ultraviolet (UV, 290-nm wavelength) laser emissions from areas of the Ce:LiCAF crystal having different doping distributions and concentrations reveal that a uniform doping distribution leads to a higher slope efficiency, lower laser threshold and a potentially higher damage threshold even though the doping concentration is low compared to areas with high but non-uniform doping. Our results show a means of improving laser performance by aiming to achieve a uniform doping distribution; and multi-photon luminescence and LA-ICPMS are powerful tools that could aid in this process. Improved laser performance could lead to new breakthroughs in laser output energies especially in the UV region for many applications.

Highly efficient and wide range low temperature sensing of upconversion luminescence of NaYF4: Er[formula omitted] nanoparticles: Effects of concentration of active or sensitive ions, excitation power and particle size on temperature sensing sensitivity

In this article, NaYF4: Er3+ nanoparticles (NPs) with/without codoping Yb3+ ions were successfully synthesized by the co-precipitation method. The temperature sensing performance of upconversion luminescence of β-NaYF4: Er3+ under 980 nm excitation was investigated based on the fluorescence intensity ratio (FIR) technology in the temperature range from 113 K to 443 K. The maximum absolute and relative temperature sensitivity were calculated to be 0.0075 K−1 at 443 K and 2.96 %K−1at 183 K, respectively. Moreover, the relative sensitivity was over 2.0 %K−1 in the temperature range from 148 K to 248 K. The effects of excitation power, size and structure of particles and concentration of codoping Yb3+ ions on temperature sensitivity were investigated, respectively. The optimum temperature sensing performance of NaYF4: Er3+ was achieved at low excitation power of 0.542 W. While increasing the particle size, coating a NaYF4 layer or codoping Yb3+ ions is harmful to temperature sensing performance. The results indicate that NaYF4: Er3+ NPs have great application prospect in low temperature nanothermometer and present a great reference for future study of optical nanothermometer.

Characterization of the Ce,Pr:LuAG phosphor for Co-doped aerosol phosphor thermometry

The Ce,Pr:LuAG phosphor is investigated for use in co-doped aerosol phosphor thermometry (APT). The phosphor was characterized by measuring the emission intensity for each ion as a function of excitation laser fluence and temperature. A simplified three-level model was used to interpret and fit the data. The phosphor was then used for co-doped APT temperature-imaging experiments performed in a heated air jet up to a maximum temperature of 694 K. The three-level model fit was used to analyze sources of bias in the imaging measurements. Both ions’ emission intensities show a nonlinear dependence on excitation fluence that can potentially be explained by temperature-dependent ground- and excited-state absorption processes included in the three-level model. Single-shot temperature precision from the temperature-imaging experiments was measured to be 22, 23, and 32 K for mean temperatures of 497, 603, and 694 K, respectively, at a spatial resolution of ~1.12 lp/mm and average fluence of 33 mJ/cm2. The results extend the measurement range for co-doped APT to at least 700 K. The findings also provide a simple model for phosphor signal non-linearity with excitation fluence for low activator ion concentrations, and provide a method for estimating temperature bias from several sources including laser fluence.

Impact of SO42\u2212, Ca2+, and Mg2+ ions in Caspian Sea ion-engineered water on the rate of wettability alteration in carbonates

Tuning the salinity and concentration of potential-determining ions, such as Mg2+, Ca2+, and SO42−, could alter the wettability toward a more water-wet state. The rate of alteration in carbonate rock wettability is a critical parameter to design the duration of the ion-engineered water flooding. Characteristic experiments, such as dynamic contact angle and pH measurements, ion chromatography, and spontaneous imbibition, are applied to study the rate of wettability alteration using different samples of ion-engineered water. Our study shows that the Caspian Sea water (CSW) with a salinity of 15,000 ppm is an efficient displacing fluid as it can initiate the multi-ion exchange (MIE) mechanism and alter the wettability from 86° to 35° within 2 d. The adjustment of salinity and active ion concentration makes the MIE mechanism much faster. For example, with five times diluted CSW, the same change in wettability is only achieved only within 9 h. Spiking the concentration of Ca2+ and SO42− ions is used to further shift the contact angle to 22° within 9 h. Spontaneous imbibition tests demonstrate that the rate of oil production doubles as a result of the ion-engineered brine due to the faster MIE process. The results obtained from this research work suggest that even a short period of interaction with optimized engineered water can affect the brine, oil, and carbonates interactions and change the reservoir rock initial wettability from neutral to strongly water-wet state. This allows to efficiently design engineered water flooding based on CSW in the field scale and make such projects more profitable.

Terbium-doped calcium germanate (Ca2GeO4) as a potential candidate for LED application

Powder samples of Ca2GeO4 doped with 0.5, 1, 2 and 3 at.% Tb3+ were prepared via solid-state synthesis technique. The obtaining of pure phase at all dopant concentrations was proved through XRD analyses. In the emission and excitation spectra of the obtained powders, the characteristic peaks of Tb3+ ion were observed. The Tb3+ excitation spectrum in the range from 300 to 500 nm shows characteristic transitions of Tb3+, attributed to the f–f transitions. The strongest peak is located at 379 nm corresponding to the 7F6 → 5D3 transition. The main emission peak of Tb3+ is 5D4 → 7F5 transitions at 545 nm, corresponding to green color. Other transitions are located at 416 (5D3 → 7F5), 437 (5D3 → 7F4), 458 (5D3 → 7F3), 488 (5D4 → 7F6), 588 (5D4 → 7F4), 621 (5D4 → 7F3), 651 (5D4 → 7F2) and 675 (5D4 → 7F1) nm. The optimum emission is observed for 2 at.% Tb3+ ion concentration. At this concentration dominate also (5D4 → 7F4) and (5D4 → 7F3) transitions. CIE coordinates of the samples show different emission colors depending on the active ion concentration. The obtained results confirm that as-prepared terbium-doped materials could be used like green, yellow and reddish phosphors.