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Red/near infrared (NIR) long persistent phosphors have received extensive attentions in biomedical, food inspection, iris recognition, biological imaging, etc. Herein, a new phosphor, Li2ZnGe3O8:Cr3+, is reported with deep red persistent luminescence peaking at 708 nm. By adjusting the Cr3+ doping concentration, the competitive site occupation at [ZnO6] and [GeO6] polyhedral enables different traps behaviors including trap types, trap concentration and trap depth, which in turn leads to different afterglow duration time from 2 to 20 h. The persistent luminescence mechanisms originated from different trap models have been discussed, and it is found that they can cooperate or inhibit each other, enabling different luminescence depending on time. The dynamic anti‐counterfeiting applications have been demonstrated, which provides a new way to rationally designing for multi‐functional luminescent materials. [ABSTRACT FROM AUTHOR]

Recently, near-infrared phosphors that can be applied in many fields such as night vision, agriculture, and bio-applications have attracted considerable interest in the research field worldwide. Herein, a multi-functional and dual-excited near-infrared phosphor Mg14Ge5O24:Cr3+,Cr4+ which provides two emission bands ranging from 700 nm to 1100 nm and 1100 nm to 1700 nm has been obtained via the traditional high-temperature solid state reaction. The presence of six and four coordination ions in the olivine structure of Mg14Ge5O24 provides a favorable environment for the coexistence of Cr3+ and Cr4+. Under blue light excitation, a super broad emission band ranging from 650 nm to 1100 nm with a full-width at half maximum (FWHM) of 266 nm is assigned to the spin-allowed 4T2 (4F) → 4A2 transition of Cr3+ in a weak crystal-field environment. With the increase in the concentration of Cr ions, more and more Cr4+ preferentially occupies four coordinated Ge4+ sites, and the other broad emission band ranging from 1100 nm to 1600 nm with a FWHM of 256 nm that comes from the 3T2 → 3A2 transition of Cr4+ is observed. The phenomenon of NIR I region excitation and NIR II region emission appears. The transmission experiment of a biological tissue proves that the Mg14Ge5O24:Cr3+,Cr4+ phosphor has potential applications in the field of near-infrared light-emitting diodes for biological detection. [ABSTRACT FROM AUTHOR]

Currently, the mechanism of Ce 3+ -Eu 2+ ET is frequently used to obtain color adjustable or white phosphors. Correspondingly, the ET efficiency from Ce 3+ to Eu 2+ becomes an important indication of the luminescent properties of phosphors. However, the ET efficiency calculated using the formula does not always match the emission spectra; the transmission efficiency of Ce 3+ is high, but the emission efficiency of Eu 2+ is low, depending on our investigation results. In addition to this problem, here we mainly review, on the basis of substantial examples, how to boost the actual ET efficiency of Ce 3+ -to-Eu 2+ and thus to improve the luminescent properties of phosphors through the rational design of layered crystal structure and the way of selective occupation of activator ions. Moreover, the possible physical mechanisms are proposed., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

In recent years, efforts have been made to develop narrow-band emission phosphors with excellent performance. Herein, a series of KScSr 1- y Ca y Si 2 O 7 :0.07Bi 3+ narrow-band phosphors were synthesized by a co-substitution method, and the crystal structure, the occupancy of activated ions and luminescence properties were studied in detail. The substitution of Ca 2+ for Sr 2+ ions resulted in the migration of the activated Bi 3+ from the K site to Sr site, accompanied by the regulation of the emission peak from 410 nm to 455 nm, the peak emission half width from 52 nm to 40 nm, and the color purity from the original 78% to 88%. In addition, a warm white LED with low CCT = 3401 K, CRI = 95.5, and CIE color coordinates of (0.3447, 0.3682) has been obtained through the combination of KSS 0.6 C 0.4 S:0.07Bi 3+ with a commercial green and red phosphor on a UV (370 nm) chip. The results not only provided a strategy based on the manipulation of chemical composition and crystal structure to tune spectral distribution, but also broadens the choice of activators of narrow-band blue-emitting phosphors., Competing Interests: The authors declare that they have no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

Near-infrared spectroscopy is developing rapidly in the fields of human detection and food analysis due to its fast response and non-invasive characteristics. Herein, we report the novel near-infrared garnet-type Ca 3 In 2 Ge 3 O 12 : x Cr 3+ and Ca 3 In 2- x Ga x Ge 3 O 12 :0.07Cr 3+ phosphors, in which there are two crystallographic sites (CaO 8 , InO 6 ) that can be substituted by Cr 3+ , and cation regulation engineering for In 3+ is utilized to tune the luminescence properties. Under the 480 nm excitation, the Ca 3 In 2 Ge 3 O 12 : x Cr 3+ phosphor emits a broad spectrum at 650-1150 nm, which matches well with the first biological window. The concentration quenching mechanism and luminescence mechanism of Ca 3 In 2 Ge 3 O 12 : x Cr 3+ were studied and the site assignment of the two luminescence centers was discussed using low temperature spectra and fluorescence decay curves. The application performance of the phosphor was improved by introducing Ga 3+ to substitute for In 3+ , and the blue shift of nearly 50 nm was explained by crystal field and nephelauxetic effects. At the same time, a 24% increase in the activation energy of thermal quenching of phosphors was obtained, which has been analyzed using the mechanism of phonon transition and the change of structural rigidity. Thus, the near-infrared emitting Ca 3 In 0.2 Ga 1.8 Ge 3 O 12 :0.07Cr 3+ phosphor was obtained, which has lower cost, higher emission intensity, and much better thermal stability, spreading the application of phosphors in plant far red light illumination, human body detection, and spectral conversion technology of silicon-based solar cells. Simultaneously, an example of a near-infrared plant illumination experiment is given, demonstrating that a cation substitution strategy based on crystal field control could be applied to tune spectral distribution and develop novel potential phosphors for practical optical application., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

Recently, near-infrared phosphors that can be applied in many fields such as night vision, agriculture, and bio-applications have attracted considerable interest in the research field worldwide. Herein, a multi-functional and dual-excited near-infrared phosphor Mg 14 Ge 5 O 24 :Cr 3+ ,Cr 4+ which provides two emission bands ranging from 700 nm to 1100 nm and 1100 nm to 1700 nm has been obtained via the traditional high-temperature solid state reaction. The presence of six and four coordination ions in the olivine structure of Mg 14 Ge 5 O 24 provides a favorable environment for the coexistence of Cr 3+ and Cr 4+ . Under blue light excitation, a super broad emission band ranging from 650 nm to 1100 nm with a full-width at half maximum (FWHM) of 266 nm is assigned to the spin-allowed 4 T 2 (4F) → 4 A 2 transition of Cr 3+ in a weak crystal-field environment. With the increase in the concentration of Cr ions, more and more Cr 4+ preferentially occupies four coordinated Ge 4+ sites, and the other broad emission band ranging from 1100 nm to 1600 nm with a FWHM of 256 nm that comes from the 3 T 2 → 3 A 2 transition of Cr 4+ is observed. The phenomenon of NIR I region excitation and NIR II region emission appears. The transmission experiment of a biological tissue proves that the Mg 14 Ge 5 O 24 :Cr 3+ ,Cr 4+ phosphor has potential applications in the field of near-infrared light-emitting diodes for biological detection.