Tunable white light and energy transfer of Eu2+-Tb3+-Eu3+ tri-activated glasses synthesized in air

An ever increasing demand for white light-emitting diodes (W-LEDs) results in the gradual growth of research on functionalized luminescent glasses. In this paper, single-composition tunable white-emitting Eu²⁺-Tb³⁺-Eu³⁺ tri-activated glasses were synthesized by melt quenching method without additional reducing atmosphere. The coexistence of Eu²⁺ and Eu³⁺ was confirmed by ultraviolet-visible transmission spectra, photoluminescent spectra, fluorescence decay curves, and X-ray photoelectron spectroscopy. Tb³⁺ can act as bridge to connect Eu²⁺-Eu³⁺ luminescent centers by energy transfer. Tone-tunable white light can be achieved by coupling the emission centered at 412, 541, and 612 nm contributed from Eu²⁺, Tb³⁺, and Eu³⁺, respectively. By adjusting the relative content of Eu²⁺/Tb³⁺/Eu³⁺, ideal chromaticity coordinates of (0.33, 0.33) can be achieved under excitation of ultraviolet light. High thermal stability and tiny chromaticity shift were exhibited in samples. These results suggest that Eu²⁺-Tb³⁺-Eu³⁺ tri-activated glasses have great potential application in ultraviolet-driven W-LEDs.     

Toward tunable and bright deep‐red persistent luminescence of Cr3+ in garnets

Garnet structure (A₃B₂C₃O₁₂) with three different cation sites is a very flexible host material widely used for w‐LEDs, solid‐state lasers, scintillators, and so on. In this work, we have successfully developed six different Cr³⁺‐doped garnets: Y₃Ga_4.99Cr_0.01O₁₂ (YGG:Cr), Gd₃Ga_4.99Cr_0.01O₁₂ (GGG:Cr), Lu₃Ga_4.99Cr_0.01O₁₂ (LuGG:Cr), Y₃Sc_1.99Cr_0.01Ga₃O₁₂ (YSGG:Cr), Gd₃Sc_1.99Cr_0.01Ga₃O₁₂ (GSGG:Cr), and Lu₃Sc_1.99Cr_0.01Ga₃O₁₂ (LuSGG:Cr), which exhibit persistent luminescence (PersL) due to Cr³⁺ emission matching well with both the response curve of the Si detector and the wavelength region of the first biological window (NIR‐I, 650‐950 nm). The main emission band of Cr³⁺ in these garnets can be easily tunable from the sharp R‐line emission due to the ²E (²G)→⁴A₂ (⁴F) transition in the strong crystal field to the broad band emission due to the ⁴T₂ (⁴F)→⁴A₂ (⁴F) transition in the weak one when Lu³⁺ in the A site and Ga³⁺ in the B site are, respectively, replaced by larger cations, Y³⁺/Gd³⁺ and Sc³⁺. Furthermore, based on the knowledge of 4f energy levels of 15 lanthanide ions in the host‐referred binding energy (HRBE) diagram, we took the GSGG host as a typical example to discuss the feasibility of four trivalent lanthanides (Sm³⁺, Eu³⁺, Tm³⁺, Yb³⁺) as potential sensitizers for enhancing Cr³⁺ PersL.     

Near white light emission of Ce3+‐, Ho3+‐, and Sm3+‐doped oxyfluoride silicate glasses

The Ce³⁺‐, Ho³⁺‐, and Sm³⁺‐ single and co‐doped oxyfluoride silicate glasses for light emitting diodes are studied. These glasses were prepared by melt quenching method and their optical and structural properties were investigated by absorption spectra, photoluminescence spectra, Commission International de I'Eclairage chromaticity coordinates, X‐ray diffraction, and Fourier transform infrared spectra. It is found that the introduction of Al₂O₃ in glass composition can improve the emissions of Ho³⁺ and Sm³⁺. While the presence of B₂O₃ has the adverse effect and can suppress the emissions of Ho³⁺ and Sm³⁺. With substituting Na₂O for CaO in the glass compositions, CaF₂ crystals can be formed during the melt quenching process. We find the formation of CaF₂ crystals can change the emission behavior of Ho³⁺ and Sm³⁺ ions. White light emissions can be achieved in the glasses and the luminescence colors can be tuned by varying the concentrations of the doped rare‐earth ions and the composition of glass matrix. The Ce³⁺‐, Ho³⁺‐, and Sm³⁺‐doped oxyfluoride silicate glasses presented here demonstrate promising applications in the fields of light emitting diodes.     

Nd3+‐Doped Silicate Glasses as an Efficient Color Filter to Improve the Color Gamut of a White LED

Nd³⁺‐doped silicate glass (Nd‐glass) was employed as a color filter for a white LED based on red and green phosphor (RG‐LED), to manipulate the photoluminescence spectral shape and thus to provide a wider color gamut. The hypersensitive transition of Nd³⁺:⁴I_9/2→⁴G_5/2,²G_7/2 was adjusted via glass composition and Nd concentration, and improved absorbance as well as reduced the absorption bandwidth. The effective absorption of the Nd‐glass at ~580 nm reduced the spectral linewidth of the green and red emissions, improving the color reproduction range. The color gamut of the RG‐LED was improved from 75.3% to 81.6% NTSC by the introduction of Nd‐glass as a color filter. Reliability under high operating current and high temperature were also examined and discussed.     

Role of Nd3+ ions on the nucleation and growth of PbS quantum dots (QDs) in silicate glasses

The influence of Nd₂O₃ addition on the precipitation kinetics of lead chalcogenide (PbS) quantum dots (QDs) in silicate glasses was investigated. Energy dispersive X‐ray spectroscopy (EDS) indicated that the Nd³⁺ ions are preferentially located inside the PbS QDs rather than in the glass matrix. Changes in diameter (D) of PbS QDs exhibited smaller time dependencies (i.e., D≈t^{0.270‐0.286}) than that predicted by the classical Lifshitz–Slyozov–Wagner (LSW) theory. This is due to the limited concentrations of Pb²⁺ and S^2? ions and the large diffusion distance inside the glass matrix. In addition, extended X‐ray absorption fine structure (EXAFS) results indicated that the formation of PbS QDs was retarded due to the presence of Nd₂O₃ in the glasses, as the large NdO_x polyhedra interrupt the diffusion of Pb²⁺ and S^2? ions. We believe that these Nd³⁺ ions are primarily located in PbS QDs in the form of Nd–O clusters, and that the PbS QDs are built on top of these clusters.     

Spectral management and energy‐transfer mechanism of Eu3+‐doped β‐NaGdF4:Yb3+,Er3+ microcrystals

β‐NaGdF₄:Yb³⁺,Er³⁺ upconversion (UC) microcrystals were prepared by a facile hydrothermal process with the assistance of ethylene diamine tertraacetic acid (EDTA). The β‐NaGdF₄ UC microcrystal morphology was controlled by changing the doses of EDTA and NaF. Uniform hexagonal structure can be obtained at the 2 mmol EDTA and 9‐10 mmol NaF. The UC emissions of β‐NaGdF₄:Yb³⁺,Er³⁺ microcrystals were tuned by the variation of Eu³⁺ doping level (0%‐5%), where the red/green intensity ratio decreased with the Eu³⁺ concentration increase. It was found on the base of rate equations that with the Eu³⁺ doping, the energy back transfer process ²H_11/2/⁴S_3/2 (Er³⁺) → ⁴I_13/2 (Er³⁺) decreased. In addition, an energy‐transfer process from ⁴F_7/2 (Er³⁺) to ⁵D₁ (Eu³⁺) and a cross relaxation process of ⁷H_9/2 (Er³⁺) + ⁵D₀ (Eu³⁺) → ⁴F_7/2 (Er³⁺) + ⁵D₂ (Eu³⁺) were proposed and verified by rate equations, which dominated the energy‐transfer mechanism between Er³⁺ and Eu³⁺, resulted in the spectra tuning of β‐NaGdF₄:Yb³⁺,Er³⁺. The results suggested that the color tuning of β‐NaGdF₄:Yb³⁺,Er³⁺,Eu³⁺ UC microcrystals would have potential applications in such fields as flat‐panel displays, solid‐state lasers, and photovoltaics.     

Emission from Mo‐O charge‐transfer state and Yb3+ emission in Eu3+‐doped and nondoped molybdates under UV excitation

Molybdates of Li⁺ and Yb³⁺ are studied to investigate the luminescence under UV excitation. LiYb(MoO₄)₂ and Eu³⁺‐doped LiYb₁‐_xEux(MoO₄)₂ (x=001–1.0) phosphors were synthesized by solid state reaction under mixing of Eu₂O₃, Yb₂O₃, Li₂CO₃ and MoO₂ in air atmosphere. Two broad absorption bands centered at 333 and 236 nm are observed in LiYb(MoO₄)₂ compound. They are attributed to the ¹A₁→¹T₁ and ¹T₂ transitions due to the O^2?→Mo⁶⁺ electron transfers in MoO₄ tetrahedron. An emission band with a peak at about 440 nm is found, which is attributed to the ³T₁→¹A₁ transition of MoO₄. Appearance of near‐infrared (NIR) Yb³⁺ emission observed under UV excitation is understood by the MoO₄→Yb³⁺ Foerster‐Type energy transfer due to spectral overlap between the low‐energy tail of the broad 440 nm emission band and the high‐energy tail of the broad Yb³⁺ absorption band and due to short Yb³⁺‐MoO₄ distance. Yb³⁺ emission observed in LiYb_1?xEu_x(MoO₄)₂ by Eu³⁺ excitation is understood by the Eu³⁺→Yb³⁺ energy transfer by cross‐relaxation (CR) process between the ⁵D₀→⁷F₆ Eu³⁺ transition and the ²F_7/2→²F_5/2 Yb³⁺ transition. The CR efficiency shows maximum efficiency of 0.24 at x=0.15 of higher acceptor Yb³⁺ concentration than donor Eu³⁺ concentration. Three Yb³⁺ emission bands with peaks at 994, 1002, and 1023 nm are observed, depending on the excitation wavelength. This is explained by less‐shielded 4f electrons of Yb³⁺ by the 5s²5p⁶ outermost electron shells, which are also responsible for unusual broadband Yb³⁺ absorption and emission. From appearance of NIR Yb³⁺ emission under excitation by not only UV light but also red light, these compounds are expected to be suitable for efficient photovoltaic application to Si‐based solar cells.     

Luminescence properties and tunable emission of Ag NCs in oxyfluoride glass through REF3 (RE = Y,La and Gd) doping

In this research, series of Ag nanoclusters (Ag NCs) contained oxyfluoride glasses were prepared using the melt quenching method, in which the REF₃ (RE = Y, La, and Gd) were selected as dopants to control their size distribution. The absorption, steady and time‐resolved PL spectra were carried to investigate the size dependent luminescence properties of Ag NCs. The spectral results indicated that the super broadband emission of Ag NCs is contributed by the spin‐allowed (blue side) and the spin‐forbidden (red side) transitions, respectively. Besides, the introduction of REF₃ (RE = Y, La, and Gd) can promote the formation of Ag NCs with different sizes and therefore modulated their luminescence properties. The maximum external quantum yields of Ag NCs with emissions at 430, 510, 520, and 570 nm were evaluated to be 24.6%, 40.7%, 56.3% and 30.7%, respectively, which can be obtained in SAg, SAgLa, SAgGd, and SAgY.     

Preparation and photoluminescence properties with the site‐selected excitations of Bi3+‐activated Ba3Sc4O9 phosphors

A series of novel Bi³⁺‐doped Ba₃Sc₄O₉ phosphors were synthesized through the solid‐state reaction. Their photoluminescence, decay curves, and thermal quenching properties were investigated in detail. The Ba₃Sc₄O₉:Bi³⁺ phosphors could be efficiently excited in the ultraviolet and near‐ultraviolet region (300‐400 nm), and the photoluminescence properties possess an obvious site‐selected excitations phenomenon. When excited at the ultraviolet light (320‐360 nm), the phosphors present a green or a bluish green emission, and when excited at the near‐ultraviolet light (370‐390 nm), the phosphors always show a yellow emission. The emission spectra excited at the different wavelength can be decomposed into four components, which accord with the four cationic sites in the structure of Ba₃Sc₄O₉. The influence of the Bi³⁺ concentration on the photoluminescence properties is also investigated. Upon excitation at 330 and 377 nm, the Ba₃Sc₄O₉:Bi³⁺ both have good thermal quenching properties; their emission intensity of the peak at 150°C both exceed 60% of the initial value. The above results indicate that the Ba₃Sc₄O₉:Bi³⁺ phosphor is a promising candidate to provide green or yellow components for UV or near‐UV LEDs.     

Synthesis of Eu3+‐doped BaBi2Ta2O9 based glass‐ceramic nanocomposites: Optical and dielectric properties

In this paper we report for the first time synthesis of Eu³⁺‐doped transparent glass‐ceramics (TGC) with BaBi₂Ta₂O₉ (BBT) as the major crystal phase using the glass system SiO₂–K₂O–BaO–Bi₂O₃–Ta₂O₅ by melt quenching technique followed by controlled crystallization through ceramming heat treatment. DSC studies were conducted in order to determine a novel heat‐treatment protocol to attain transparent GCs by controlling crystal growth. The structural properties of the BBT GCs have been investigated using XRD, FE‐SEM, TEM and FTIR reflectance spectroscopy. Optical band gap energies of the glass‐ceramic samples were found to decrease with respect to the precursor glass. An increased intensity of emission along with increase in the average lifetime of Eu³⁺ was observed due to incorporation of Eu³⁺ ions into the low‐phonon energy BBT crystal site. The local field asymmetric ratios of all the samples were observed greater than unity. The dielectric constant (ε_r), dielectric loss, and dissipation factor values of both the base glass and ceramized samples were found to decrease with increase in frequency.     

Synthesis and Optical Properties of Rare-Earth–Aluminum Oxide Glasses

Single-phase glasses containing 37.5 mol% Y₂O₃, 7 mol% La₂O₃, and 1 mol% Pr, Ho, Nd, Er, Sm, Tm, Eu, or Yb oxide substituted for part of the Y₂O₃ were synthesized by containerless melting. The spectral transmission and absorption cross sections of the glasses were determined at wavelengths from 360 to 3300 nm. The electronic transitions were broadened compared with results obtained in a crystalline yttrium aluminum garnet (YAG) host. The infrared transmission of the host glass extended to 6000 nm. The optical and physicochemical properties of these glasses are well suited for optical device applications.     

Nonlinear negative transmittance at a CW 980‐nm laser diodes pumping in Yb3+:CaF2 nanocrystals‐embedded glass ceramics

Cooperative upconversion luminescence (CUCL) occurs in spectral regions in which single ions do not have energy levels. However, all results reported so far are concentrated on luminescence properties from Yb³⁺ ions‐doped various hosts. Here, we report the observation of nonlinear negative transmittance (NNT) at continuous‐wavelength (CW) 980‐nm laser diodes (LDs) pumping in silicate oxyfluoride glass ceramics (GCs)‐containing CaF₂:Yb³⁺ nanocrystals. The unique optical nonlinearity is analyzed based on energy‐level transitions, dynamic evolution, rate equation, and power transmission equation, which can be explained as the cooperative optical absorption for the intense CUCL of Yb³⁺ ions. The NNT in the CaF₂:Yb³⁺ nanocrystals‐embedded GCs can be tailored with the power of a CW 980‐nm LDs, which possesses potential for the development of future optical limiters and switches.     

Efficient red‐emitting phosphor of Eu3+‐activated (Na0.5Gd1.5)(TiSb)O7 derived via cation‐substitutions in Gd‐Pyrochlore

Rare‐earth (RE) titanate pyrochlore with perovskite‐layered structure is a well‐known engineering material in applied in many field. In this work, a red‐emitting phosphor of Gd_2?xNa_xTi_2?2xSb_2xO₇:Eu³⁺ (x = 0‐0.5) was developed via cation substitutions of (Sb⁵⁺→Ti⁴⁺) and (Na⁺→Gd³⁺) in Gd₂Ti₂O₇. The motivation is based on the fact that the introduction of cation‐disorders has been regarded to be an effective approach for improving the luminescent efficiency and thermal stability of RE‐activated materials. All the samples were synthesized via facile solid‐state reaction method. The morphology properties were measured via SEM and EDS measurements. The structural Rietveld refinement was performed to investigate the microstructure in pyrochlore lattices. The luminescence properties of Gd_2?xNa_xTi_2?2xSb_2xO₇:0.15Eu³⁺ (x = 0‐0.5) has a strict dependence on the cation substitution levels. The band energy of Gd₂Ti₂O₇ is 2.9 eV with a direct transition nature. The incorporation of Sb⁵⁺ and Na⁺ in the lattices moves the optical absorption to a longer wavelength. The cation disorder results in significant improvements of luminescence intensity, excitation efficiency in the blue region, longer emission lifetime and thermal stability.     

Light‐induced electrons suppressed by Eu3+ ions doped in Ca11.94−xSrxAl14O33 caged phosphors for LED and FEDs

Control of light‐induced electron generation is of vital importance for the application of caged phosphors. For Eu‐doped Ca_11.94?xSr_xAl₁₄O₃₃ caged phosphors, the suppressed effect of strontium doping on the light‐induced electrons is observed compared to the europium‐free Ca_11.94?xSr_xAl₁₄O₃₃ phosphors. In the presence of europium ions, Sr doping will promote the reduction of Eu³⁺ to Eu²⁺. The Rietveld refinement suggests that unit cell volumes of the Ca_11.94?xSr_xAl₁₄O₃₃:Eu_0.06 samples are expanded when Ca²⁺ ions are replaced by Sr²⁺ ions. The absorption and FTIR transmittance spectra confirm that the competitive reaction of encaged O^2? anions with H₂ is suppressed. For the sample (x=0.48), the higher thermal activation energy (~0.40 eV) for luminescence quenching can be attributed to the more rigid framework structure after Sr doping. For Ca_11.94?xSr_xAl₁₄O₃₃:Eu_0.06 phosphors, their emission colours are tuned from red to purple upon 254 nm excitation and from pink to blue under electron beam excitation through Sr substitution. The insight gained from this work may have a significant guiding to design new phosphors for LED and FEDs and novel nanocaged mutifunctional materials.     

Synthesis and photoluminescence of novel blue-emitting phosphor of Eu2+-activated fluoroborate BaGaBO3F2

Pure and Eu²⁺-activated fluoroborate BaGaBO₃F₂ was prepared using high-temperature solid-state reaction. BaGaBO₃F₂ is a wide band semiconductor with the indirect transition characteristic. The excitation and luminescence spectra of the phosphor were measured, and it was found that Eu²⁺-activated BaGaBO₃F₂ exhibits a bright blue color under ultraviolet (UV) light. The narrow emission band peaked at 425 nm is attributed to the transitions of 4f⁶5d→4f⁷(⁸S_7/2), and the Stokes shift estimated for this phosphor sample is 3140 cm⁻¹. The lifetime of the luminescence is also reported. The absolute quantum efficiency (QE) of the phosphor was evaluated, and it was found that the absolute QE decreases with increasing Eu²⁺ concentration. The phosphor shows an excellent quantum efficiency of 72.5% and a high thermal activation energy of 0.342 eV. The study concludes that Eu²⁺-doped BaGaBO₃F₂ phosphor has promising luminescence application abilities and can be used as a blue-emitting phosphor in a variety of applications.     

Enhanced electrical properties and strong red light‐emitting in Eu3+‐doped Sr1.90Ca0.15Na0.9Nb5O15 ceramics

The luminescent‐ferroelectic materials based on Sr_1.90Ca_0.15Na_0.9Nb₅O₁₅ (SCNN) matrix doping with Eu³⁺ were synthesized by the conventional solid‐state reaction method. The crystal structure, photoluminescence, thermal stability, dielectric, ferroelectric, and piezoelectric behaviors were systematically investigated. XRD results revealed that Eu³⁺ introduction could induce the tungsten bronze phase transition from orthorhombic to tetragonal structures. The dielectric spectra of all specimens showed two broad dielectric anomalies: a high‐temperature ferroelectric phase transition (T_c) and a low‐temperature ferroelastic phase transition (T_s), both of which were suppressed at higher Eu³⁺ concentrations. The enhanced electrical properties were obtained in a proper Eu³⁺ concentration range of 0.03‐0.05. For all SCNN:xEu³⁺ samples, the strong red emission peak at 617 nm originating from the electric dipole transition of ⁵D₀ →⁷F₂ was excited by different light excitations of 395 or 463 nm. Our results demonstrated that Eu³⁺‐doped SCNN materials might have promising potential in advanced multifunctional optoelectronic applications.     

Thermal effects of Er3+/Yb3+‐doped NaYF4 phosphor induced by 980/1510 nm laser diode irradiation

The thermal effects of Er/Yb‐doped NaYF₄ phosphor induced by 980/1510 nm laser diode irradiation were intuitively and contrastively investigated using an infrared thermal imaging technology with real‐time online monitoring. The Yb³⁺/Er³⁺ codoped materials have strong thermal effects and high‐temperature elevation under 980 nm irradiation. However, the severe thermal effects of materials with higher Er³⁺ ion doping concentration are remarkably attributed to the cross relaxation between the Er³⁺ ions under 980 nm irradiation. The energy transfer between Er³⁺ and Yb³⁺ ions in Er³⁺/Yb³⁺‐codoped materials also contributes to the thermal effects under 1510 nm laser diode irradiation. Under the same testing conditions, the temperature elevation ?T of samples induced by 1510 nm laser diode irradiation is lower than that induced by 980 nm laser diode irradiation. The temperature rising rate and elevation ?T value of samples depend on the ion doping concentration and power density of the laser diode excitation. The internal temperature of the samples exhibits deep temperature gradient under 980/1510 nm laser diode irradiation. By comparing the two kinds of thermometry methods, the temperature value calculated by fluorescence intensity ratio is almost similar to that obtained through infrared thermal imaging technology under higher excitation power pumping.     

Synthesis and Unique Photoluminescence Properties of Eu2Ti2O7 and Eu2TiO5

The europium titania materials, pyrochlore Eu₂Ti₂O₇ and orthorhombic Eu₂TiO₅, were synthesized from a mixture of Eu₂O₃ and TiO₂ using the solid‐state reaction method. The structural and optical properties of these titania materials were investigated using X‐ray diffraction analysis, photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, and diffuse reflectance spectroscopy. Temperature dependence of the PL intensity was measured between T = 20 and 450 K and analyzed on the basis of various theoretical models. A remarkable increase in the PL intensity with increasing T was observed in these titania materials at higher temperatures, above ~140 K, and well explained by a trap/reservoir model. Interestingly, a dramatic decrease in the electric‐dipole emission component relative to the magnetic‐dipole one was observed in Eu₂Ti₂O₇ above T ~ 140 K. The schematic energy‐level diagram for Eu³⁺ in the Eu₂Ti₂O₇ host was proposed for the sake of a better understanding of the PL and PLE processes in this type of phosphorescent material.     

A Single‐Phase Phosphor NaLa9 (GeO4)6O2: Tm3+, Dy3+ for Near Ultraviolet‐White LED and Field‐Emission Display

Single‐phase white‐light‐emitting phosphors NaLa_9(1?x?y) (GeO₄)₆O₂: xTm³⁺, yDy³⁺ (NLGO: xTm³⁺, yDy³⁺) have been synthesized by a traditional solid‐state reaction method. The powder X‐ray diffraction (XRD), photoluminescence (PL), PL excitation (PLE) spectra, fluorescence decay curves, chromaticity coordinates, correlated color temperature (CCT), and the cathodoluminescence (CL) properties of the obtained phosphors are measured and discussed in detail. It is discovered that the series samples could be color‐tunable (from blue to yellow) by tuning the doping content of Dy³⁺ with a fixed Tm³⁺ content excited at 357 nm and white light (0.341, 0.324) could be obtained with the CCT of 5079 K. A NLGO: 0.01Tm³⁺, 0.02Dy³⁺ is studied carefully as representative. The main emissions of Tm³⁺ (453 nm, ¹D₂–³F₄) and Dy³⁺ (478 nm, ⁴F_9/2–⁶H_15/2; 572 nm, ⁴F_9/2–⁶H_13/2) make it emit white light with good thermal stability (67% of the initial till 523 K). The energy transfer from Tm³⁺ to Dy³⁺ is noticed and further research has been done to explain the enhancement of Dy³⁺ emission and the excellent thermal stability. It also keeps stable under continuous electron bombardment with high intensity. All of these indicate that it could be a suitable candidate for white‐emitting phosphor applied for near ultraviolet‐white light‐emitting diode (NUV‐WLED) and field‐emission display (FED).     

Sol-gel route to nanocrystalline Eu2Ti2O7 films with tailored structural and optical properties

We present a generic sol-gel approach for the preparation of highly transparent europium titanate Eu₂Ti₂O₇ films with tailored structural and optical properties. The films were prepared by a sol-gel process and thermally treated in a rapid thermal annealing furnace. We determined the effects of the annealing temperature on structural, morphological, and optical properties of the films. We evaluated film's optical constants. The size of the primary nanocrystals and the film's refractive index were tailored by the annealing temperature. The crystallization of Eu₂Ti₂O₇ started at 800°C and the nanocrystals grew with increasing annealing temperature reaching the size from 20 nm to 100 nm. The energy of nanocrystal growth was 21 ± 3 kJ·mol⁻¹. Increasing nanocrystal size caused the regular growth of the refractive index recorded at 632 nm from 2.07 to 2.17 for the films annealed at 800°C and 1200°C, respectively. These results provide fundamental information about the effects of the structure and the morphology of the films on their optical properties. The presented approach can be extended to other rare earth-doped titanates and these films can be used as passive protective coatings as well as active materials suitable for photonic and spintronic applications.