Photoluminescence Decay Kinetics Research Articles

Photoluminescence study of anatase TiO2 photocatalysts at the pico- and nanosecond timescales.

We studied the photoluminescence decay kinetics of three nanosized anatase TiO2 photocatalysts (particle diameter: 7, 25, or 200nm) at the pico- and nanosecond timescales for elucidating the origin of the luminescence. Luminescence spectra from these photocatalysts obtained under steady-state excitation conditions comprised green luminescence that decayed on the picosecond timescale and red luminescence that persisted at the nanosecond timescale. Among the photocatalysts with different sizes, there were marked differences in the rate of luminescence decay at the picosecond timescale (<600ps), although the spectral shapes were comparable. The similarity in the spectral shape indicated that self-trapped excitons (STEs) directly populated in the bulk of the particle by light excitation emit the luminescence in a picosecond timescale, and the difference in the rate of luminescence decay originated from the quenching at the particle surface. Furthermore, we theoretically considered excitation light intensity dependence on the quantum yield of the luminescence and found that the quenching reaction was not limited by the diffusion of the STEs but by the reaction at the particle surface. Both the spectral shape and time-evolution of the red luminescence from the deep trapped excitons in the nanosecond timescale varied among the photocatalysts, suggesting that the trap sites in different photocatalysts have different characteristics with respect to luminescence. Therefore, the relation between trap states and photocatalytic activity will be elucidated from the red luminescence study.

Study of Intrachain Charge Transfer in a Blue Emissive Polyfluorene Random Copolymer.

Photophysics of a blue light-emitting fluorescent random copolymer, consisting of arylated polydioctylfluorene (aryl-F8), polydioctylfluorene (F8), and amine comonomers in a ratio of 80:15:5 is reported. In a solution of 10-6 M, solvatochromism in absorption and photoluminescence (PL) is observed with an increased lifetime of PL as the polarity of the solvent increases. Dual fluorescence is observed in the 10-9 M diluted solution, comprising a structured emission from a localized state in the aryl-F8 comonomer and a broad emission peak from the charge-transfer (CT) state at a lower energy. Emission wavelength-dependent time-resolved photoluminescence studies in different polar media confirm the presence of the emissive intrachain CT state in this copolymer. Analyzing the PL decay kinetics, we calculated the formation rate of the intrachain CT state to be ∼3.0 × 109 s-1. Repopulation of the localized state from the CT state is observed in the lower polarity medium with a rate of 7 × 108 s-1, which is almost absent for the large Stokes-shifted CT emission in the higher polarity medium. Along with the fundamental understanding of the photophysics of the random copolymer, this study suggests that the emission spectrum can be tailored by the concentration of polymer and the polarity of surrounding media.

Carbon nitride coupled with carbon nanohorns for improved photocatalytic hydrogen production and dyes degradation

In the present study we attempted to develop photoactive nanocomposites via the facile coupling of carbon nitride (CN) with single walled carbon nanohorns (CNHs). Photocatalytic activity was evaluated for the degradation of Rhodamine B (RhB) and the production of H2. The CNHs content noticeably affected the photoactivity of the nanocomposites and the best performing material exhibited a 3-fold increase in photocatalytic H2 production compared to pristine CN using 1 wt% Pt as co-catalyst. A systematic study was undertaken to explain the mechanistic aspects of the photo-reaction process. The active species responsible for the photodegradation of RhB were identified using reference reactions. Such species were further studied using in-situ spin-trap EPR experiments. Photoluminescence and time-resolved fluorescence decay kinetics suggested faster transfer of photogenerated electron/hole pairs resulting in reduced charge recombination phenomena in the nanocomposites. The combined photocatalytic application and characterization of the prepared materials revealed that the promotion of the redox reactions in based on improvements on the charge separation efficiency.

Spectroscopic properties and photoluminescence of the Li2B4O7:Mn,Sm glass

The Li2B4O7:Mn,Sm glass containing 1.0 mol.% MnO2 and Sm2O3 were researched by X-ray diffraction (XRD), electron paramagnetic resonance (EPR), and optical spectroscopy methods. The studied glass of high optical quality was obtained by high temperature melting technique. Parameters of the local structure (interatomic distances and coordination numbers) of Li2B4O7:Mn,Sm glass were derived from XRD data analysis. The EPR and optical spectroscopy (absorption, luminescence excitation, emission, decay kinetics) show the presence of Mn2+(3d5) and Mn3+(3d4) impurity ions in the Li2B4O7:Mn,Sm glass. By EPR spectroscopy in the studied glass were identified three types of Mn2+ centres: single Mn2+ (1) centres in the strongly distorted sites (ratio of rhombic and axial constants, |E/D| ≤ 1/3), single Mn2+ (2) centres in the sites with almost cubic symmetry (D ≅ 0, E ≅ 0) as well as Mn2+ pairs and small clusters coupled by magnetic dipolar and exchange interaction, respectively. The Mn2+ EPR spectra parameters in the Li2B4O7:Mn,Sm glass have been determined at T = 295 K. Optical absorption spectrum of the Li2B4O7:Mn,Sm glass contains a very broad intense band peaked at 467 nm belonging to the 5Eg(D) → 5T2g(D) transition of Mn3+ ions and several weak narrow lines corresponding to the 6H5/2 → 6P3/2, 6H5/2 → 6F9/2, 6F7/2, 6F5/2 transitions of Sm3+ (4f5, 6H5/2) ions. Emission spectrum of the Li2B4O7:Mn,Sm glass exhibits a broad band corresponding to the 4T1g(G) → 6A1g(S) transition of Mn2+ ions and three characteristic bands in the yellow-orange-red range belonging to the 4G5/2 → 6H5/2, 6H7/2, 6H9/2 transitions of Sm3+ ions. Photoluminescence spectra (excitation and emission) and decay kinetics of the Mn2+ and Sm3+ ions in the Li2B4O7:Mn,Sm glass are interpreted in comparison with corresponding results for Li2B4O7:Mn and Li2B4O7:Sm glasses. Energy transfer processes Sm3+→Mn2+, Mn3+, and Mn2+→Mn3+ in the studied glass are considered.

Luminescent manifestations of ytterbium ions in the crystal structure of silicate apatite

The manifestation of ytterbium ions in the microcrystals of the Sr2Y6.8YbSi6O26:Er0.2 solid solution with apatite structure was studied on the basis of low-temperature photoluminescence (PL) spectroscopy and spectral-kinetic measurement data. Intracenter down-conversion luminescence of Er3+ ions in the visible and IR ranges was detected. Up-conversion luminescence of Er3+ ions is observed upon IR excitation due to excitation of Yb3+ ions and subsequent energy transfer Yb3+ → Er3+. Overlapping bands at 412 and 430 nm with a Stokes shift of less than 0.3 eV are observed in the PL spectra at room temperature. These emission bands are assigned to the spin-allowed and spin-forbidden 4f135d → 4f14 transitions from the low-spin and high-spin exciting states of Yb2+ ion, respectively. The PL decay kinetics for transitions from the low-spin states is characterized by a dominant component τ = 0.39 ns. An alternative model of Yb3+ luminescence center associated with a charge transfer band does not explain the data of low-temperature (5K) PL spectroscopy. At T = 5 K, a new wide emission band with a maximum at 696 nm and a Stokes shift of 1.1 eV appears in the PL spectrum. Two options of this PL band nature are considered. The first is the luminescence of defects having a vacancy nature. The second possible option is the manifestation of anomalous luminescence of Yb2+ ions, which occupy a different crystallographic position in the apatite crystal structure.

Regularities of Manganese Charge State Formation and Luminescent Properties of Mn-Doped Al2O3, YAlO3, and Y3Al5O12 Single Crystalline Films

In this work, three sets of single crystalline films (SCF) of Al2O3:Mn sapphire, YAlO3:Mn perovskite (YAP:Mn), and Y3Al5O12:Mn garnet (YAG:Mn), with a nominal Mn content of 0.1%, 1%, and 10 atomic percent (at.%) in the melt-solutions, were crystallized by the liquid phase epitaxy (LPE) method onto sapphire, YAP and YAG substrates, respectively. We have also calculated the average segregation coefficient of Mn ions for Al2O3:Mn, YAP:Mn and YAG:Mn SCFs with Mn content in the melt-solution in the 0.1–10% concentration range, which was equal to 0.1, 0.14 and 0.2, respectively. The main goal of the conducted research was the spectroscopic determination of the preferable valence states of manganese ions which were realized in the SCFs of sapphire, perovskite and garnet depending on the Mn content. For this purpose, the absorption, cathodoluminescence (CL), photoluminescence (PL) emission/excitation spectra and PL decay kinetics of Al2O3:Mn, YAP:Mn and YAG:Mn SCFs with different Mn concentrations were studied. Based on the CL and PL spectra, we showed that Mn ions, depending on the Mn content in the melt-solution, are incorporated in Al2O3:Mn, YAP:Mn and YAG:Mn SCFs in the different charged states and are located in the different crystallographic positions of the mentioned oxide lattices. We have observed the presence of the luminescence of Mn4+, Mn3+ and Mn2+ valence states of manganese ions in CL spectra in all SCFs under study with 0.1 and 1% Mn concentrations. Namely, the Mn4+ ion valence state with the main sharp emission bands peaked at 642 and 672 nm, related to the 2E → 4A2 transitions, was found in the luminescence spectra of the all studied Al2O3:Mn SCFs. The luminescence of the Mn2+ valence state was found only in YAP:Mn and YAG:Mn SCFs, grown from melt solution with 1% Mn content, in the emission bands peaked at 525 and 560 nm, respectively, related to the 4T1 → 6A1 transitions. The PL and CL spectra of YAP:Mn and YAG:Mn SCFs with the Mn content in the 0.1–1% range show that the main valence state of manganese ions in these films is Mn3+ with the main emission bands peaking at 655 and 608 nm, respectively, related to the 1T2 → 5E transitions. Meanwhile, higher than 1% Mn content in the melt solution causes a strong concentration quenching of luminescence of all Mn centers in Al2O3:Mn, YAP:Mn and YAG:Mn SCFs.

Near-Infrared Emitting of Zero-Dimensional Europium(II) Halide Scintillators: Energy Transfer Engineering via Sm2+ Doping

Near-infrared (NIR)-emitting scintillators, coupled with high quantum efficiency silicon-based photodetectors, have emerged as a promising solution for highly efficient radiation detection applications. However, the study of efficient NIR-emitting scintillators and their associated luminescence mechanism is still limited. In this work, we developed NIR-emitting zero-dimensional Cs4EuBr6 halide scintillators via Sm2+ doping. Single crystals of Cs4EuBr6 with varying Sm2+ concentrations were grown by the vertical Bridgman method. Under X-ray irradiation, the scintillation emission of highly Sm-doped Cs4EuBr6 single crystals is dominated by the Sm2+ 5d–4f emission peaking at 831 nm with a weak Eu2+ 5d–4f emission peaking at 443 nm. The energy transfer processes between Eu2+ and Sm2+ were investigated by using photoluminescence (PL) spectra, PL decay kinetics, and soft X-ray excited decay kinetics measurements. Based on the temperature-dependent PL decay results, we constructed a configurational coordinate diagram of Sm2+ in the Cs4EuBr6 host. Furthermore, we evaluated the gamma spectroscopy response of Cs4EuBr6:Sm single crystals using an avalanche photodiode detector known for its high sensitivity in the NIR wavelength region.

Probing the Förster Resonance Energy Transfer Dynamics in Colloidal Donor-Acceptor Quantum Dots Assemblies.

In this article, we report the synthesis of graphene quantum dots (GQDs) by hydrothermal method and surface modified CdS quantum dots (QDs) via the colloidal method and the fabrication of their dyad. The CdS QDs functionalized by mercaptoacetic acid (MAA) attach to the GQDs via electrostatic interactions. Spectral overlapping between the emission spectrum of GQDs and the absorption spectrum of CdS QDs allows efficient Förster resonance energy transfer (FRET) from GQDs to the CdS QDs in the GQDs-CdS QDs dyads. The magnitude of FRET efficiency (E) and the rate of energy transfer (kE) assessed by the photoluminescence (PL) decay kinetics are ~61.84% and ⁓3.8 × 108s- 1, respectively. These high values of FRET efficiency and energy transfer rate can be assigned to the existence of strong electrostatic interactions between GQDs and CdS QDs, which arise due to the presence of polar functionalities on the surface of both GQDs and CdS QDs. The understanding of energy transfer in the luminescent donor-acceptor FRET system is of significant importance and the practical implications of such FRET systems could overall improve the efficiency of photovoltaics, sensing, imaging and optoelectronic devices.

Gd-doped silica fiber fabricated using surface plasmachemical deposition with view to radiation sensor applications

A Gd3+-doped-silica optical fiber free of other codopants in the core was fabricated with the help of surface plasma chemical vapor deposition (SPCVD) for the first time. The SPCVD-process parameters are described as well as the fiber properties in the as-drawn state (absorption and photoluminescence (PL) spectra upon excimer-laser excitation at λ = 276 and 193 nm and PL decay kinetics) and during γ-irradiation at 1–3.5 Gy/s up to 0.5–1.4 kGy (radiation-induced absorption (RIA) and radioluminescence (RL)). The 315-nm RL band is argued to be suitable for real time dose-rate monitoring, although RIA and persistent luminescence can influence the RL intensity. The possibility to suppress RIA on completion of irradiation by thermal annealing at 500 °C during 15 min was demonstrated.

Thermally stable Sm3+ -doped alkali zinc alumino borosilicate (AZABS) glass for warm white light generation and w-LED applications.

Samarium ion (Sm3+ )-doped alkali zinc alumino borosilicate (AZABS) glass was synthesized via quick melt quench technique. Various spectroscopic studies like optical absorption, photoluminescence (PL) emission, PL excitation, temperature-dependent PL and PL decay kinetics were performed on the as prepared glass system. Under 402 nm excitation, three sharp bands at wavelengths 563, 599 and 645 nm corresponding to transitions 4 G5/2 → 6 H5/2 , 6 H7/2 and 6 H9/2 , respectively, can be seen in the PL emission spectra. The 0.25 mol% Sm3+ glass has the highest intensity for these emissions. The lanthanide interaction in the glass matrix is dipole-dipole in nature as was proven from Dexter's analysis. The direct bandgap of 0.25 mol% Sm3+ -doped AZABS glass was calculated to be 2.88 eV. The lifetimes of the as prepared glass range from 1.93 ms for the lowest concentration of Sm3+ to 0.75 ms for the highest. From temperature dependent PL studies, the activation energy for 0.25 mol% Sm3+ -doped AZABS glass was found to be 0.19 eV which shows high thermal stability of this glass. We propose to utilize these Sm3+ -doped AZABS glasses for white-light emitting diodes (w-LEDs) and solid-state lighting (SSL) applications.

Statistical Analysis of Photoluminescence Decay Kinetics in Quantum Dot Ensembles: Effects of Inorganic Shell Composition and Environment.

Discerning the kinetics of photoluminescence (PL) decay of packed quantum dots (QDs) and QD-based hybrid materials is of crucial importance for achieving their promising potential. However, the interpretation of the decay kinetics of QD-based systems, which usually are not single-exponential, remains challenging. Here, we present a method for analyzing photoluminescence (PL) decay curves of fluorophores by studying their statistical moments. A certain combination of such moments, named as the n-th order moments' ratio, R n , is studied for several theoretical decay curves and experimental PL kinetics of CdSe quantum dots (QDs) acquired by time-correlated single photon counting (TCSPC). For the latter, three different case studies using the R n ratio analysis are presented, namely, (i) the effect of the inorganic shell composition and thickness of the core-shell QDs, (ii) QD systems with Förster resonance energy transfer (FRET) decay channels, and (iii) system of QDs near a layer of plasmonic nanoparticles. The proposed method is shown to be efficient for the detection of slight changes in the PL kinetics, being time-efficient and requiring low computing power for performing the analysis. It can also be a powerful tool to identify the most appropriate physically meaningful theoretical decay function, which best describes the systems under study.

Luminescence and photoconversion properties of micro-powder phosphors based on the Ce3+ and Mn2+ doped Ca2YMgScSi3O12 silicate garnets

This work is dedicated to study the synthesis processes and luminescence properties of micro-crystalline powder phosphors of Ce3+ and Mn2+ doped Ca2YMgScSi3O12 garnets (CYMSSG:Ce and CYMSSG:Ce,Mn) The photoluminescence emission spectra and decay kinetics confirm the formation of Ce3+ multicenters in the CYMSSG:Ce powder phosphor due to local inhomogeneity of the different dodecahedral positions and presence of the energy transfer between high-energy and low energy Ce3+ emission centers in this garnet. The effective Ce3+ to Mn2+ energy transfer process is observed in CYMSSG:Ce, Mn phosphors resulting in the redshift of the emission spectra in comparison with CYMSSG:Ce counterpart. We have shown that CYMSSG:Ce and CYMSSG:Ce, Mn powder phosphors can be used as an efficient photoconverter (PC) for creation of the high-power white LEDs (WLEDs). The prototypes of PC-WLEDs, based on 450 nm emitting blue LED and planar layers of CYMSSG:Ce and CYMSSG:Ce, Mn microcrystalline powder phosphors, embedded in the epoxy resin, were prepared and their photoconversion properties were investigated as well.

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.

Photoluminescence of metallic single-walled carbon nanotubes: Role of interband and intraband transitions

The photoluminescence (PL) properties of metallic single-walled carbon nanotubes were investigated. Steady-state measurements showed interband excitonic PL in the first hyperbolic dispersion region. The decay kinetics of this interband excitonic PL was observed by femtosecond time-resolved measurements, which also showed the occurrence of intraband PL in the linear dispersion region. The decay time constant of interband excitonic PL is approximately 40 fs, while that of intraband PL is slower at the lower photon energy. This study demonstrates the role of interband and intraband transitions in the PL of a one-dimensional metal.

Sm3+ photoluminescence and excited-state dynamics in lithium-barium borate glasses co-doped with CuO

• Lithium-barium borate glasses containing Sm 2 O 3 and CuO prepared by melting. • Characterizations performed by XRD, FT-IR, UV/Vis/NIR and photoluminescence spectroscopies. • Influence of CuO on Sm 3+ luminescence investigated through PL decay kinetics. • Efficient Sm 3+ → Cu 2+ energy transfer indicated due to strong spectral overlap. The effect of CuO co-doping on orange/red-emitting Sm 3+ -doped borate glasses prepared by melting was investigated by various spectroscopic techniques. The glasses were first characterized by X-ray diffraction and Fourier transform-infrared spectroscopy for basic structural properties. Absorption spectroscopy showed that CuO addition leads to the development of the Cu 2+ absorption band around 735 nm. Photoluminescence (PL) spectra obtained for the CuO-free reference glass under 250 nm excitation displayed host-sensitized Sm 3+ PL along with intrinsic band emission from the borate host. The CuO doping produced a new contribution to band emission characteristic of Cu + . Further, significant decrease of Sm 3+ visible luminescence was evidenced in accord with a quenching effect induced by Cu 2+ . The analysis of Sm 3+ emission decay curves harmonized with the occurrence of two populations of Sm 3+ ions (single, interacting). The two decay components showed significant 4 G 5/2 lifetime decrease with increasing CuO content demonstrating an efficient Sm 3+ → Cu 2+ energy transfer.

Specific features of Stokes photoluminescence of the La2S3–Ga2S3–Er2S3 glasses

Series glasses with compositions (100–х-y) Ga2S3 – х La2S3 – y Er2S3 (х = 30, 35, 40; y = 0, 1, 3 mol.%) were synthesized and their optical properties were examined. Glass-forming region for the novel La2S3–Ga2S3 system was determined. Composition−dependent optical absorption spectra within the spectral range 480–1020 nm and photoluminescence (PL) under excitation by laser radiation with 532 nm wavelength were measured. The PL maxima were found at 660, 810, 860, 980 and 1540 nm. The origin of the excited states in Er3+ ions was analyzed using an energy diagram. PL decay kinetics processes were analyzed in detail, within the frame of the two exponents model. This one indicates that the Erbium ions emitting in both red and IR spectral ranges are embedded in the glass matrices a like as separate ions or form clusters of erbium ions. The presented research results along with literature data indicate a wide opportunity for potential applications like thermal and radiation sensors, non-linear optical triggers, up-converters, contactless thermometers or active media for IR lasers.

Strain Adjustment Realizes the Photocatalytic Overall Water Splitting on Tetragonal Zircon BiVO4.

Overall water splitting to generate H2 and O2 is vital in solving energy problem. It is still a great challenge to seek efficient visible light photocatalyst to realize overall water splitting. In this work, the tetragonal zircon BiVO4 is prepared by epitaxial growth on FTO substrate and its overall water splitting reaction is studied. Under the influence of epitaxial strain, the conduction band position shifts negatively and beyond H+/H2 reduction potential (0 V vs NHE), which enables it to possess the photocatalytic hydrogen evolution activity. After loading cocatalysts, the overall water splitting (λ > 400 nm) is realized (H2: ≈65.7 µmol g−1 h−1, O2: ≈32.6 µmol g−1 h−1), and the value of solar hydrogen conversion efficiency is 0.012%. The single‐particle photoluminescence (PL) spectra and PL decay kinetics tests demonstrate the cocatalysts are beneficial to the separation and transfer of carriers. The new strategy of adjusting the band structure by strain is provided.

Gd-admixed (Lu,Gd)AlO3 single crystals: breakthrough in heavy perovskite scintillators

We report a breakthrough concept for a bulk single crystal as a heavy aluminum perovskite scintillator, where due to bandgap engineering by a balanced Gd admixture in a Lu cation sublattice, the scintillation performance dramatically increases. In an optimized composition of (Lu, Gd)AlO3:Ce (LuGdAP:Ce), the light yield approaches 21,000 phot/MeV, which is close to that of classical but much less dense YAP:Ce and 50% higher than the best LuYAP:Ce reported in the literature. Moreover, contrary to LuYAP:Ce, the LuGdAP host maintains a high effective atomic number close to that of LuAP:Ce (Zeff = 64.9), which is comparable to commercial LSO:Ce. An enormous decrease in afterglow on the millisecond time scale and acceleration in the rise time of the scintillation response further increase the application potential of the LuGdAP host. The related acceleration of the transfer stage in the scintillation mechanism due to diminishing electron trap depths is proven by thermally stimulated luminescence (TSL). Furthermore, we quantitatively characterize and model the energy transfer processes that are responsible for the change in the photoluminescence and scintillation decay kinetics of Ce3+ in the LuGdAP matrix. Such an innovative (Lu, Gd)AP:Ce scintillator will become competitive for use in applications that require heavy, fast, and high light yield bulk scintillators.

Effective surface passivation on CsPbBr3 nanocrystals via post-treatment with aromatic carboxylic acid

Surface defects on CsPbX3 nanocrystals (NCs) commonly lead to the degeneration of photoluminescence emission and stability of CsPbX3 NCs. Defect passivation by surface engineering provides an effective route to improve the optical properties and stability. In this work, a series of aromatic carboxylic acids were explored to modify the as-synthesized CsPbBr3 NCs. The surface defects of CsPbBr3 NCs are found to be effectively passivated via the binding of carboxyl group with uncoordinated Pb2+ on the surface of CsPbBr3 NCs. The coordination ability of carboxyl groups with Pb2+ can be regulated by the electron effect generated by different groups at the para-position of carboxyl groups, thereby adjusting the passivation of surface defects. Benefitting from the effective passivation of surface defects, the PL emission and stability of the CsPbBr3 NCs can be effectively enhanced. Among them, the CsPbBr3 NCs modified with the softest 4-(trifluoromethyl)benzoic acid show near-unity photoluminescence quantum yields, a single-exponential photoluminescence decay kinetics and excellent stability.

Nd3+-doped TiO2 nanocrystals: Structural changes, excited-state dynamics, and luminescence defects

The structural and optical properties of the TiO2 nanocrystals (NCs) samples pure and doped with Nd3+ ions were studied as a function of temperature. These properties were studied by using the Raman spectroscopy, steady-state and time-resolved photoluminescence. A structural transformation is observed by a systematic study as a function of the temperature from room temperature. The results show that the introduction of Nd3+ ions and the increase of temperature induces a phase transformation from anatase to brookite. As a result, the intrinsic defects states of TiO2 NCs decrease and consequently the PL intensity of the 4F3/2 level of Nd3+ ions increases. The photoluminescence decay kinetics also shows that Nd3+ ions are located in two different environments of TiO2 NCs: the brookite and anatase phase.