Recent startling interest for lanthanide luminescence is stimulated by the continuously expanding need for luminescent materials meeting the stringent requirements of telecommunication, lighting, electroluminescent devices, (bio-)analytical sensors and bio-imaging set-ups. This critical review describes the latest developments in (i) the sensitization of near-infrared luminescence, (ii) “soft” luminescent materials (liquid crystals, ionic liquids, ionogels), (iii) electroluminescent materials for organic light emitting diodes, with emphasis on white light generation, and (iv) applications in luminescent bio-sensing and bio-imaging based on time-resolved detection and multiphoton excitation (500 references).

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Lanthanide luminescence for functional materials and bio-sciences

Applications in Theranostics Guanying Chen,*,†,‡ Hailong Qiu,†,‡ Paras N. Prasad,*,‡,§ and Xiaoyuan Chen* †School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin, Heilongjiang 150001, China ‡Department of Chemistry and the Institute for Lasers, Photonics, and Biophotonics, University at Buffalo, State University of New York, Buffalo, New York 14260, United States Department of Chemistry, Korea University, Seoul 136-701, Korea Laboratory of Molecular Imaging and Nanomedicine, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, Maryland 20892-2281, United States

Upconversion Nanoparticles: Design, Nanochemistry, and Applications in Theranostics

Interpretation of europium(III) spectra

Temperature (T) is probably the most fundamental parameter in all kinds of science. Respective sensors are widely used in daily life. Besides conventional thermometers, optical sensors are considered to be attractive alternatives for sensing and on-line monitoring of T. This Review article focuses on all kinds of luminescent probes and sensors for measurement of T, and summarizes the recent progress in their design and application formats. The introduction covers the importance of optical probes for T, the origin of their T-dependent spectra, and the various detection modes. This is followed by a survey on (a) molecular probes, (b) nanomaterials, and (c) bulk materials for sensing T. This section will be completed by a discussion of (d) polymeric matrices for immobilizing T-sensitive probes and (e) an overview of the various application formats of T-sensors. The review ends with a discussion on the prospects, challenges, and new directions in the design of optical T-sensitive probes and sensors.

Luminescent probes and sensors for temperature.

Non-invasive precise thermometers working at the nanoscale with high spatial resolution, where the conventional methods are ineffective, have emerged over the last couple of years as a very active field of research. This has been strongly stimulated by the numerous challenging requests arising from nanotechnology and biomedicine. This critical review offers a general overview of recent examples of luminescent and non-luminescent thermometers working at nanometric scale. Luminescent thermometers encompass organic dyes, QDs and Ln3+ions as thermal probes, as well as more complex thermometric systems formed by polymer and organic–inorganic hybrid matrices encapsulating these emitting centres. Non-luminescent thermometers comprise of scanning thermal microscopy, nanolithography thermometry, carbon nanotube thermometry and biomaterials thermometry. Emphasis has been put on ratiometric examples reporting spatial resolution lower than 1 micron, as, for instance, intracellular thermometers based on organic dyes, thermoresponsive polymers, mesoporous silica NPs, QDs, and Ln3+-based up-converting NPs and β-diketonate complexes. Finally, we discuss the challenges and opportunities in the development for highly sensitive ratiometric thermometers operating at the physiological temperature range with submicron spatial resolution.

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Thermometry at the nanoscale

Combustion synthesized Gd 2 O 3 : Er 3+ /Yb 3+ nanocrystalline phosphor has been developed and used as a temperature sensor. Frequency upconverted emissions from two thermally coupled excited states 2 H 11/2 and 4 S 3/2 of Er 3+ centered at 523 and 548 nm in the phosphor pumped by NIR source were recorded in the temperature range 300–900 K. The maximum sensitivity derived from the FIR technique of the green upconversion emission is approximately 0.0039 K −1 . The results imply that Er 3+ /Yb 3+ codoped Gd 2 O 3 phosphor can play an important role in high temperature measurements with a better sensitivity.

Er3+/Yb3+ codoped Gd2O3 nano-phosphor for optical thermometry

Fluorescence characteristics of Dy3+ ions in calcium fluoroborate glasses

Lanthanide based materials are preferred over other luminescent materials for various applications. Current focus in this area is to exploit the unique luminescence features of lanthanide-based materials for multidisciplinary research and novel applications. Furthermore, efforts are going on to enhance the luminescence of lanthanide ions for better performance. In a broader sense, there are two ways to enhance the luminescence of lanthanide ions. The first is to use a suitable sensitizer, which can absorb excitation energy efficiently, and can transfer it to the lanthanide ions. This method has been known for a long time and is well documented in the literature. The second way is to modify host matrices in such a way that it favors radiative transitions. It is widely reported in the literature that the presence of alkali ions, particularly Li+ ions, in a matrix enhances the luminescence of lanthanide ions significantly. But there are no comprehensive reports available in the literature that summarize how alkali ions help in the luminescence enhancement of lanthanide ions in various host matrices. The prime objective of this review is to highlight various contributing factors that help in the luminescence enhancement of lanthanide ions in the presence of alkali ions.

Role of Li+ ion in the luminescence enhancement of lanthanide ions: favorable modifications in host matrices

A dual mode rare-earth based oxide phosphor (Y0.977Yb0.02Er0.003NbO4), demonstrating both down conversion (DC) and upconversion (UC) emission, has been developed using a facile solid state reaction method which can be easily scaled-up for large quantities. In the DC studies, the material exhibits a strong blue emission with a long decay time (4.36 μs), corresponding to the charge transfer band of [NbO4]3− under UV excitation (262 nm), and a green emission of the Er3+ ions under blue (379 nm) excitation. Furthermore, it has been noticed that under infrared (976 nm) excitation, this phosphor shows strong green and red emission along with relatively weak emission bands in the UV-blue and IR regions, which confirm the compatibility of this phosphor for UC too. In the UC emission, the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of the Er3+ ion portray a temperature dependent behaviour and have been used for temperature sensing (optical thermometry) using the fluorescence intensity ratio (FIR) method. The maximum sensitivity is found to be 0.0073 K−1 at 473 K, which is better in comparison with other host matrixs reported so far. The results suggest that this dual mode phosphor could be an exceptional choice for next generation luminescence-based temperature sensing devices as well as in advanced display devices.

S.B. Rai

Papers

Er3+/Yb3+ codoped Gd2O3 nano-phosphor for optical thermometry

Fluorescence characteristics of Dy3+ ions in calcium fluoroborate glasses

Role of Li+ ion in the luminescence enhancement of lanthanide ions: favorable modifications in host matrices

Probing a highly efficient dual mode: down-upconversion luminescence and temperature sensing performance of rare-earth oxide phosphors.

Vibrational spectrum of glycine molecule.