An indenocarbazole-based host material for solution processable green phosphorescent organic light emitting diodes

We designed and synthesized a new host material with a highly soluble and thermally stable indenocarbazole derivative (7,7-dimethyl-5-phenyl-2-(9-phenyl-9H-carbazol-3-yl)-5,7-dihydro-indeno[2,1-b]carbazole) that can make green phosphorescent organic light-emitting diodes (PHOLEDs) in a solution process. In particular, these are used in a blue common layer structure in which green and red-emitting layers are formed by a solution process and blue common layers are thermally evaporated. The new host material possesses excellent hole transport capability and high triplet energy (T₁). Mainly we designed the hole dominant material to keep the exciton forming area away from the hole transport layer (HTL) and emitting layer (EML) interface, an interfacial mixing area to improve device performance. As a result, the greatest lifetime of 1300 hours was achieved and a high current efficiency of up to 66.3 cd A⁻¹ was recorded when we used the optimized device structure of a 5 nm thick bipolar exciton blocking layer (B-EBL). It may be a good agreement of exciton confinement and reduced electron accumulation at the HTL and EML interface.

We designed and synthesized a new host material with a highly soluble and thermally stable indenocarbazole derivative that can make green phosphorescent organic light-emitting diodes (PHOLEDs) in a solution process.     

Oxadiazole derivatives as bipolar host materials for high-performance blue and green phosphorescent organic light-emitting diodes

By combining two n-type groups, pyridine and oxadiazole, with one p-type carbazole group, two novel bipolar hosts, namely 2-(3-(9H-carbazol-9-yl)-[1,1′-biphenyl]-3-yl)-5-(pyridin-2-yl)-1,3,4-oxadiazole (PyOxd-mCz) and 2-(4′-(9H-carbazol-9-yl)-[1,1′-biphenyl]-3-yl)-5-(pyridin-2-yl)-1,3,4-oxadiazole (PyOxd-pCz) have been developed as hosts for blue and green phosphorescent organic light-emitting diodes (PhOLEDs). The two compounds exhibit similar HOMO levels of −5.64 eV for PyOxd-mCz and −5.63 eV for PyOxd-pCz and the same LUMO level of −2.60 eV. With a more twisted configuration due to meta connections, PyOxd-mCz possesses a higher triplet energy level (E_T = 2.77 eV) and more balanced carrier transport than PyOxd-pCz (E_T = 2.60 eV). PyOxd-mCz hosted devices achieve a peak current efficiency of 39.7 cd A⁻¹ and a maximum EQE of 20.8% with a low turn-on voltage of 3.5 V for FIrpic and 55.2 cd A⁻¹ and 16.4% for Ir(ppy)₃. Apart from the appropriate frontier molecular orbital levels and sufficiently high triplet energy of PyOxd-mCz, the more balanced carrier transport plays a key role for excellent device performance.

A high performance blue OLED has been realized by adjusting the ratio of n-type groups of the molecule and obtaining more balanced charge transport.     

Modulation for efficiency and spectra of non-doped white organic light emitting diodes by combining an exciplex with an ultrathin phosphorescent emitter

Herein, structured non-doped white organic light-emitting diodes (WOLEDs) were designed by combining the emission of a blue exciplex and orange-red phosphorescent ultrathin layer. The device efficiency and spectra were modulated successfully by adjusting the thickness of the exciplex layer and ultrathin layer, respectively. Meanwhile, high efficiency with external quantum efficiency (EQE) ranging from 15% to 22%, power efficiency from 33 lm W⁻¹ to 47 lm W⁻¹ and warm white emission with correlated color temperature (CCT) from 1600 K to 2600 K were realized. The energy transfer process and emission mechanism is also discussed, and the results reveal that the efficient charge trapping and recombination contribute to the improvement of device efficiency and reduce the roll-off efficiency.

Non-doped WOLED with modulated efficiency and spectra were designed by combining blue exciplex with orange-red phosphorescent ultrathin layer.     

Rational design of quinoxaline-based bipolar host materials for highly efficient red phosphorescent organic light-emitting diodes

Two novel bipolar carbazole/diphenylquinoxaline-based host materials 3-(2,3-diphenylquinoxalin-6-yl)-9-phenyl-9H-carbazole (M1) and 3-(4-(2,3-diphenylquinoxalin-6-yl)phenyl)-9-phenyl-9H-carbazole (M2) have been rationally designed and synthesized. The phenyl spacer between the functionalized quinoxaline moiety and the carbazole moiety is also introduced to investigate its influence on their photophysical properties. The chemical structures, and thermal, photophysical and electrochemical properties of the two host materials were characterized and explored in detail. Red phosphorescent light-emitting diodes with M1 and M2 as hosts were prepared to explore their electroluminescent properties. Both M1 and M2 host-based red devices exhibit outstanding electroluminescent performance. For example, two red devices all realize good red emission with the maximum at 594 nm, the maximum external quantum efficiency and luminance can reach 14.66% and 28 619 cd m⁻² for M1-based devices and 15.07% and 28 818 cd m⁻² for M2-based devices, indicating compounds M1 and M2 designed in this work have potential applications in the development of high-performance monochrome and white OLEDs.

Two novel bipolar carbazole/diphenylquinoxaline-based host materials 3-(2,3-diphenylquinoxalin-6-yl)-9-phenyl-9H-carbazole (M1) and 3-(4-(2,3-diphenylquinoxalin-6-yl)phenyl)-9-phenyl-9H-carbazole (M2) have been rationally designed and synthesized.     

Highly luminescent polyethylene glycol-passivated graphene quantum dots for light emitting diodes

The emergence of fluorescent graphene quantum dots (GQDs) is expected to enhance the usefulness of quantum dots (QDs), in terms of their unique luminescence, photostability, low toxicity, chemical resistance, and electron transport properties. Here we prepared blue-photoluminescent polyethylene glycol GQDs (PEG-GQDs) through PEG surface passivation. The photoluminescence (PL) quantum yield (QY) of PEG-GQDs with 320 nm excitation was about 4.9%, which was higher than that of pure GQDs. The as-fabricated PEG-GQDs with high QY were then used as light-emitting diode (PGQD-LED) emitters, in which the GQDs were incorporated into polymeric host layers in a multilayer electroluminescent device; blue emission with a luminance exceeding 800 cd m⁻² was achieved, thus demonstrating the potential of PEG-GQDs as emitters in electroluminescence applications. Furthermore, the fluorescence mechanism of PEG-GQDs was investigated and proved that the origin of strong fluorescence of PEG-GQDs is associated with the luminescence from intrinsic states. The highly fluorescent PEG-GQDs will allow new devices, such as multicolor LEDs, to be developed with extraordinary properties, by tailoring the intrinsic and extrinsic states.

We prepared blue-photoluminescent polyethylene glycol GQDs (PEG-GQDs) through PEG surface passivation. The PL intensity was stronger than that of pristine GQDs. These were then used as LED emitters and the fluorescence mechanism was investigated.     

Flexible top-emitting organic light emitting diodes with a functional dielectric reflector on a metal foil substrate

For flexible organic light emitting diodes (OLEDs), roll-to-roll production enables low-cost fabrication and wide-ranging applications. Choosing an appropriate substrate material is one of the critical issues in the fabrication of flexible OLEDs. We demonstrated top-emitting OLEDs with a highly reflective distributed Bragg reflector (DBR) using a metal foil substrate. The DBR, made of seven pairs of SiO₂/ZrO₂, was formed by electron-beam evaporation on metal foil and showed high reflectivity of 90.5% at λ = 500 nm. The DBR served not only as the optical reflector, but also the substrate insulating layer which enabled the electrical isolation and prevented crosstalk. The OLEDs showed an operation voltage of 6.5 V at a current density of J = 10 mA cm⁻² and maximum luminance of 17 400 cd m⁻² at J = 225 mA cm⁻². The electroluminescence property of the device could be maintained under the tensile bending condition.

We demonstrated flexible OLEDs with a DBR serving as an optical reflector and electrical passivation on a metal foil substrate.     

Experimental and modeling study of ZnO:Ni nanoparticles for near-infrared light emitting diodes

This work is devoted to the synthesis and study of the different properties of ZnO nanoparticles (NPs) doped with the Ni element. We have used a simple co-precipitation technique for the synthesis of our samples and various structural, morphological and optical techniques for their analysis. Energy-Dispersive X-ray spectroscopy (EDX) confirms the stoichiometry of the samples. The X-Ray Diffraction (XRD) patterns reveal the hexagonal wurtzite phase of polycrystalline ZnO with a P63mc space group. Debye Scherrer and Williamson–Hall methods show that the average size of crystallites is around 40 nm. Transmission electron microscopy (TEM) images confirm the XRD results. The optical spectrum of Zn_0.95Ni_0.5O shows the presence of near-band-edge (NBE) ultraviolet emission. The absorption defect bands appearing near the blue–green region and near infrared emission are attributed to the Ni²⁺ intra-3d luminescence. The electronic structure of the Ni²⁺ doped ZnO NPs confirms the T_d site symmetry of Ni²⁺ in the ZnO host crystal and leads to a perfect correlation between calculated and experimental energy levels.

This work is devoted to the synthesis and study of the different properties of ZnO nanoparticles (NPs) doped with the Ni element.     

A thermally activated delayed fluorescence exciplex to achieve highly efficient and stable blue and green phosphorescent organic light-emitting diodes

The development of a thermally activated delayed fluorescence (TADF) exciplex with high energy is of great significance in achieving highly efficient blue, green, and red organic light-emitting diodes (OLEDs) for use in full-color displays and white lighting. Highly efficient and stable blue and green phosphorescent OLEDs were demonstrated by employing a TADF exciplex (energy: 2.9 eV) based on 4-substituted aza-9,9′-spirobifluorenes (aza-SBFs). Blue PhOLEDs demonstrated a maximum current efficiency (CE) of 47.9 cd A⁻¹ and an external quantum efficiency (EQE) of 22.5% at 1300 cd m⁻² (2.5 times the values of aza-SBF-based systems), with the best blue PhOLED demonstrating a CE, power efficiency (PE) and EQE of 60.3 cd A⁻¹, 52.7 lm W⁻¹, and 26.2%, respectively. Green PhOLEDs exhibited a CE of 78.1 cd A⁻¹ and EQE of 22.5% at 9360 cd m⁻², with the best green PhOLED exhibiting a maximum CE, PE, and EQE of 87.4 cd A⁻¹, 101.6 lm W⁻¹, and 24.5%, respectively. The device operational lifetime was improved over 17-fold compared to reference devices because of the high thermal stability of the materials and full utilization of the TADF exciplex energy, indicating their potential for application in commercial OLEDs.

A high energy TADF exciplex (415 nm) based on aza-spirobifluorene derivatives was demonstrated to achieve efficient and stable PhOLEDs.     

A vanadate-based white light emitting luminescent material for temperature sensing

Calcium magnesium vanadate-europium vanadate powders with a homogeneous distribution have been prepared by a sol–gel method followed by a sintering process. The as-prepared powders show both broadband emission around 520 nm and sharp peak emission at 617 nm under UV light excitation, which are ascribed to the one-electron charge transfer transition in the VO₄ tetrahedra and the typical ⁵D₀ → ⁷F₂ transition of Eu³⁺. Energy transfer occurs between the vanadate and Eu ions. The emission color of the products can be tuned by controlling the Eu concentration and temperature. White light emission can be obtained at the Eu concentration of 15% and at room temperature. The temperature related luminescence properties have been studied for the sample with 15 mol% Eu. The intensity ratio between the broadband emission (due to VO₄ tetrahedra) and the sharp peak emission (due to Eu³⁺ ions) decreases as the temperature increases in a linear relationship. The relative sensitivity (S_R) of this luminescent temperature sensor has been calculated and a maximum has been gained at 455 K with the value equal to 1.83% K⁻¹.

White-light emitting CMV:Eu³⁺ sheets show a linear color variation depending on the ambient temperature.     

The recombination zone adjusted by the gradient doping of TPA-DCPP for efficient and stable deep red organic light emitting diodes

Deep-red organic light-emitting diodes (DR-OLEDs) or near-infrared organic light-emitting diodes (NIR-OLEDs) have a wide range of applications in real life, such as special light sources for plant growth in agriculture, optical communications, infrared imaging, infrared medical imaging and other fields. However, the device performance of DR-OLEDs is still far behind that of red, green and blue OLEDs. In addition to the well-known energy gap law, the location of the recombination region also has a significant impact on the device performance. If the recombination area is too close to the cathode, the electrons in the electron transport layer will easily cause exciton quenching. In this study, for the first time, we adopted a quantum well-like structure by changing the host (CBP) and guest (TPA-DCPP) thicknesses as the light-emitting layer to manage the position of the recombination zone, and then improved the carrier injection and transportation as well as increased the exciton recombination rate. Furthermore, we introduced a hole trap layer to reduce the current density and suppress the recombination zone movement; finally, we prepared high-brightness and high-efficiency DR-OLEDs based on the TADF material with a wavelength of 674 nm, a maximum brightness of 1151 cd m⁻² and a maximum EQE of 4.4%.

Efficient deep red organic light-emitting diodes with 4.4% external quantum efficiency (EQE) and a stable electroluminescent spectrum at 674 nm.     

Low energy consumption phosphorescent organic light-emitting diodes using phenyl anthracenone derivatives as the host featuring bipolar and thermally activated delayed fluorescence

A novel host material featuring the characteristics of bipolarity and thermally activated delayed fluorescence, 10-(4-(5,5-dimethylbenzofuro[3,2-c]acridin-13(5H)-yl)phenyl)-10-phenylanthracen-9(10H)-one (DphAn-5BzAc), has been designed and synthesized. By employing this material as the host of green emitter Ir(ppy)₂acac, we have fabricated phosphorescent organic light-emitting diodes (PhOLEDs) with two hosting schemes, which are the single host system consisting of DhAn-5BzAc and the co-host system with 1,3-bis(carbazolyl)benzene (mCP). We found that the co-host based PhOLED achieved very low energy consumption values at high brightnesses, which were only 0.5, 5.9 and 94.0 mW m⁻² at 100, 1000 and 10 000 cd m⁻², respectively. The extremely low energy consumption for DhAn-based PhOLEDs were attributed to the excellent bipolar transport properties and thermally activated delayed fluorescence characteristics.

A bipolar host material 10-(4-(5,5-dimethylbenzofuro[3,2-c]acridin-13(5H)-yl)phenyl)-10-phenylanthracen-9(10H)-one (DphAn-5BzAc) with TADF properties, has been synthesized.     

Effects of steric encumbrance of iridium(iii) complex core on performance of solution-processed organic light emitting diodes

Iridium(iii) complexes are the most frequently applied commercialized green and red emitters for organic light emitting diode (OLED) displays. Throughout years a significant research effort has been devoted to modify these compounds, in order to make them suitable for cost-effective solution-processing techniques, such as inkjet printing. To achieve this, the inherent tendency of the complex molecules to form poorly emissive aggregates needs to be suppressed. In many cases this has been achieved by an encapsulation of the iridium(iii) complex core with dendritic structures, composed of either passive or charge-transporting fragments. In order to validate this approach, we acquired three structural analogues of the conventional green emitter Ir(ppy)₃, which possess gradually increasing sterical encumberment at the complex surface. Corresponding OLEDs were examined, with three distinctively different active emissive layer compositions in terms of charge transportation characteristics. The results show that in the all scenarios the unmodified Ir(ppy)₃ outperforms the compounds with attached bulky groups. The in-device performance of the emitter is directly related to its charge trapping ability, which is being compromised in the presence of dendritic auxiliary substituents.

Attachment of bulky groups to the surface of irdium(iii) complex core obstructs its charge trapping ability and reduces OLED performance.     

Mixture of quantum dots and ZnS nanoparticles as emissive layer for improved quantum dots light emitting diodes

Recently, quantum dots based light-emitting diodes (QLEDs) have received huge attention due to the properties of quantum dots (QDs), such as high photoluminescence quantum yield (PLQY) and narrow emission. To improve the performance of QLEDs, reducing non-radiative energy transfer is critical. So far, most conventional methods required additional chemical treatment like giant shell and/or ligands exchange. However that triggers unsought shifted emission or reduced PLQY of QDs. In this work, we have firstly suggested a novel approach to improve the efficiency of QLEDs by introducing inorganic nanoparticles (NPs) spacer between QDs, without additional chemical treatment. As ZnS NPs formed a mixture layer with QDs, the energy transfer was reduced and the distance between the QDs increased, leading to improved PLQY of mixture layer. As a result, current efficiency (CE) of the QLED device was improved by twice compared with one using only QDs layer. This is an early report on utilizing ZnS NPs as an efficient spacer, which can be utilized to other compositions of QDs.

Mixture of quantum dots and ZnS nanoparticles as emissive layer for improved QLEDs by decreasing energy transfer between the QDs.     

In situ aluminium ions regulation for quantum efficiency and light stability promotion in white light emitting material

In this study, we have proposed an in situ ion regulation strategy to assemble a white-light-emitting material with high stability and efficiency. A fluorescence tunable hybrid material was first fabricated by a “ship around the bottle” method in which the fluorescent dyes, disodium 2-naphthol-3,6-disulfonate (R) and ZnO Quantum Dots (QDs), were embedded into metal–organic frameworks (MOFs) in proportion. Then, the competition coordination of aluminium ions over zinc ions to R were utilized to subtly adjust the intensity of blue fluorescence, leading to an ideal white light with Commission Internationale de l''Eclairage (CIE) coordinates of (0.30, 0.33) and a high Color-Rendering Index (CRI) value of 93%. Compared with the material fabricated by the ratio tuning of the R salt and ZnO QDs directly, the in situ ions regulation strategy enabled the final product to have a higher quantum efficiency and light stability. Moreover, this strategy also settled the non-tunable problem of fluorescence due to the competition coordination effects of aluminium ions and zinc ions in the same synthetic system. This synthetic strategy and our new findings can provide more ideas for designing new white-light-emitting materials.

An in situ ion regulation strategy to assemble white-light-emitting material with high stability and efficiency.     

Photoluminescence properties of novel Ba2Lu5B5O17:Eu3+ red emitting phosphors with high color purity for near-UV excited white light emitting diodes

A series of new red-emitting Ba₂Lu_4.98−xEu_xLa_0.02B₅O₁₇ (0.1 ≤ x ≤ 1.0) phosphors were synthesized via the high-temperature solid-state reaction method. The phase formation of the as-synthesized Ba₂Lu_4.48Eu_0.5La_0.02B₅O₁₇ phosphor was confirmed by powder X-ray diffraction analysis. It was found that La³⁺ doping resulted in the reduction of LuBO₃ impurities and thus pure phase Ba₂Lu₅B₅O₁₇ was realised. The morphology of Ba₂Lu_4.48Eu_0.5La_0.02B₅O₁₇ phosphors was studied by field emission scanning electron microscopy (FE-SEM). As a function of Eu³⁺ concentration the photoluminescence spectra and decay lifetimes were investigated in detail. Under excitation at 396 nm, a dominant red emission peak located at 616 nm (⁵D₀ → ⁷F₂) indicated that Eu³⁺ ions mainly occupied low symmetry sites with a non-inversion center in Ba₂Lu_4.48Eu_0.5La_0.02B₅O₁₇. The optimal Eu³⁺ ion concentration was found to be x = 0.5 and the critical distance of Eu³⁺ was determined to be 6.55 Å. In addition, the concentration quenching takes place via dipole–dipole interactions. The phosphors exhibited good CIE (Commission International de I''Eclairage) color coordinates (x = 0.643, y = 0.356) situated in the red region and a high color purity of 97.8%. Furthermore, the internal quantum efficiency and the thermal stability of Ba₂Lu_4.48Eu_0.5La_0.02B₅O₁₇ phosphors were also investigated systematically. The results suggest that Ba₂Lu_4.48Eu_0.5La_0.02B₅O₁₇ may be a potential red phosphor for white light-emitting diodes.

Novel Ba₂Lu₅B₅O₁₇:Eu³⁺ red emitting phosphors with high color purity were prepared for near-UV excited white light emitting diodes.     

Efficient donor–acceptor host materials for green organic light-emitting devices: non-doped blue-emissive materials with dual charge transport properties

Comparative optical, electroluminescence and theoretical studies were performed for (E)-4′-(1-(4-(2-(1-(4-morpholinophenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)phenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-[1,1′-biphenyl]-4-amine (SMPI-TPA) and (E)-4-(4-(2-(4-(2-(4-(9H-carbazol-9-yl)phenyl)-1H-phenanthro[9,10-d]imidazol-1-yl)styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)phenyl)morpholine (SMPI-Cz). These compounds show excellent thermal properties, dual charge transport properties and form thin films under thermal evaporation. Blue OLEDs (CIE: 0.16, 0.08) based on SMPI-TPA show efficient device performance (η_ex 6.1%; η_c 5.3 cd A⁻¹; η_p 5.2 lm W⁻¹) at low turn-on voltages. Both SMPI-TPA and SMPI-Cz were utilised as hosts for green OLEDs. The devices with SMPI-Cz (30 nm):5 wt% Ir(ppy)₃ exhibit maximum luminance of 20 725 cd m⁻², and η_c and η_p values of 61.4 cd A⁻¹ and 63.8 lm W⁻¹, respectively. In comparison, devices with SMPI-TPA (30 nm):5 wt% Ir(ppy)₃ exhibit high η_c and η_p values of 65.2 cd A⁻¹ and 67.1 lm W⁻¹, respectively. Maximum η_ex values of 19.6% and 23.4% were obtained from SMPI-TPA:Ir(ppy)₃ and SMPI-Cz:Ir(ppy)₃, respectively. These device performances indicate that the phenanthroimidazole unit is a tunable building unit for efficient carrier injection and it may also be employed as a host for green OLEDs.

SMPI-Cz:Ir(ppy)₃-based devices exhibit a luminance of 20 725 cd m⁻², η_c of 61.4 cd A⁻¹ and η_p of 63.8 lm W⁻¹.     

Correction: MOF-5 derived carbon as material for CO2 adsorption

Correction for ‘MOF-5 derived carbon as material for CO₂ absorption’ by Wojciech Kukulka et al., RSC Adv., 2019, 9, 18527–18537.

The authors regret that the title shown in the original article and several sentences were incorrect due to the use of the word “absorption” in place of “adsorption”. The correct title is as shown above and all instances of “absorption” in the text should be “adsorption”. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: Split-anion solvent extraction of light rare earths from concentrated chloride aqueous solutions to nitrate organic ionic liquids

Correction for ‘Split-anion solvent extraction of light rare earths from concentrated chloride aqueous solutions to nitrate organic ionic liquids’ by Mercedes Regadío et al., RSC Adv., 2018, 8, 34754–34763, DOI: 10.1039/c8ra06055j.

The authors regret that an incorrect figure caption was given for Fig. 5. The correct version is presented below.Open in a separate windowFig. 5Viscosity as a function of the temperature and the organic phase composition: (1) after loading 39 g L⁻¹ of REE in 20 v% Cy923 in [C101][NO₃], (2) pure [C101][NO₃], (3) 20 v% Cy923 in [C101][NO₃] and (4) pure Cy923.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: Facile preparation of bithiazole-based material for inkjet printed light-emitting electrochemical cell

Correction for ‘Facile preparation of bithiazole-based material for inkjet printed light-emitting electrochemical cell’ by Jingpei Huo et al., RSC Adv., 2019, 9, 6163–6168.

The authors regret that the funding information in the acknowledgements of the original article was incorrect. “Guangdong Natural Science Foundation of China (Grant No. 2018A030310350)” should be “Guangdong Natural Science Foundation of China (Grant No. 2018A1660001)”.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: A long-persistent phosphorescent chemosensor for the detection of TNP based on CaTiO3:Pr3+@SiO2 photoluminescence materials

Correction for ‘A long-persistent phosphorescent chemosensor for the detection of TNP based on CaTiO₃:Pr³⁺@SiO₂ photoluminescence materials’ by Fangfang Li et al., RSC Adv., 2018, 8, 16603–16610.

In Fig. 2(C) of the published paper the colours of the lines were switched. A correct version of the figure is shown below:Open in a separate windowFig. 2(A) Phosphorescence excitation (Ex) and emission spectra (Em) of CaTiO₃:Pr³⁺@SiO₂ (30 μg mL⁻¹) in PBS solution (10 mM, pH = 8.0), (λ_Ex = 315 nm, λ_Em = 614 nm). (B) Phosphorescence spectra of 30 μg mL⁻¹ CaTiO₃:Pr³⁺@SiO₂ with (red curve) and without (black curve) 200 μM TNP. Inset: temporal change in the phosphorescence intensity of CaTiO₃:Pr³⁺@SiO₂ after the addition of TNP. Effect of (C) pH and (D) salt concentration on the phosphorescence intensity of CaTiO₃:Pr³⁺@SiO₂ (30 μg mL⁻¹) in the absence (black line) and presence (red line) of 200 μM TNP. λ_Ex = 315 nm (error bars, SD, n = 3).The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.