Surface plasmon coupling effects on the photon color conversion behaviors of colloidal quantum dots in a GaN nanoscale hole with a nearby quantum-well structure.

To improve color conversion performance for color display application, we study the near-field-induced nanoscale-cavity effects on the emission efficiency and Förster resonance energy transfer (FRET) under the condition of surface plasmon (SP) coupling by inserting colloidal quantum dots (QDs) and synthesized Ag nanoparticles (NPs) into surface nano-holes fabricated on a GaN template and an InGaN/GaN quantum-well (QW) template. In the QW template, the inserted Ag NPs are close to either QWs or QDs for producing three-body SP coupling to enhance color conversion. Time-resolved and continuous-wave photoluminescence (PL) behaviors of the QW- and QD-emitting lights are investigated. The comparison between the nano-hole samples and the reference samples of surface QD/Ag NP shows that the nanoscale-cavity effect of the nano-hole leads to the enhancements of QD emission, FRET between QDs, and FRET from QW into QD. The SP coupling induced by the inserted Ag NPs can enhance the QD emission and FRET from QW into QD. Its result is further enhanced through the nanoscale-cavity effect. The relative continuous-wave PL intensities among different color components also show the similar behaviors. By introducing SP coupling to a color conversion device with the FRET process in a nanoscale cavity structure, we can significantly improve the color conversion efficiency. Simulation results confirm the basic observations in experiment.

Photon color conversion enhancement of colloidal quantum dots inserted into a subsurface laterally-extended GaN nano-porous structure in an InGaN/GaN quantum-well template.

To improve the color conversion performance, we study the nanoscale-cavity effects on the emission efficiency of a colloidal quantum dot (QD) and the Förster resonance energy transfer (FRET) from quantum well (QW) into QD in a GaN porous structure (PS). For this study, we insert green-emitting QD (GQD) and red-emitting QD (RQD) into the fabricated PSs in a GaN template and a blue-emitting QW template, and investigate the behaviors of the photoluminescence (PL) decay times and the intensity ratios of blue, green, and red lights. In the PS samples fabricated on the GaN template, we observe the efficiency enhancements of QD emission and the FRET from GQD into RQD, when compared with the samples of surface QDs, which is attributed to the nanoscale-cavity effect. In the PS samples fabricated on the QW template, the FRET from QW into QD is also enhanced. The enhanced FRET and QD emission efficiencies in a PS result in an improved color conversion performance. Because of the anisotropic PS in the sample surface plane, the polarization dependencies of QD emission and FRET are observed.

Nanoscale-cavity enhancement of color conversion with colloidal quantum dots embedded in the surface nano-holes of a blue-emitting light-emitting diode.

Although the method of inserting colloidal quantum dots (QDs) into deep nano-holes fabricated on the top surface of a light-emitting diode (LED) has been widely used for producing effective Förster resonance energy transfer (FRET) from the LED quantum wells (QWs) into the QDs to enhance the color conversion efficiency, an important mechanism for enhancing energy transfer in such an LED structure was overlooked. This mechanism, namely, the nanoscale-cavity effect, represents a near-field Purcell effect and plays a crucially important role in enhancing the color conversion efficiency. Here, we demonstrate the results of LED performance, time-resolved photoluminescence (TRPL), and numerical simulation to elucidate the nanoscale-cavity effect on color conversion by inserting a photoresist solution of red-emitting QDs into the nano-holes fabricated on a blue-emitting QW LED. Based on the TRPL study of the inserted QDs in a nano-hole structure fabricated on an un-doped GaN template of no QW, it is found that the emission efficiency of the inserted QDs is significantly increased due to the nanoscale-cavity effect. From the simulation study, it is confirmed that this effect can also increase the FRET efficiency, particularly for those radiating dipoles in the QWs oriented perpendicular to the sidewalls of the nano-holes. In the nanoscale-cavity effect, the enhanced near field distribution inside a nano-hole excited by a light emitter modifies its own radiation behavior through the Purcell effect such that its far-field emission becomes stronger.

Enhancement of the Modulation Response of Quantum-Dot-Based Down-Converted Light through Surface Plasmon Coupling.

In this paper, we first elaborate on the effects of surface plasmon (SP) coupling on the modulation responses of the emission of a light-emitting diode (LED) and its down-converted lights through colloidal quantum dots (QDs). The results of our past efforts for this subject are briefly discussed. The discussions lay the foundation for the presentation of the new experimental data of such down-converted lights in this paper. In particular, the enhancement of the modulation bandwidth (MB) of a QD-based converted light through SP coupling is demonstrated. By linking green-emitting QDs (GQDs) and/or red-emitting QDs (RQDs) with synthesized Ag nano-plates via surface modifications and placing them on a blue-emitting LED, the MBs of the converted green and red emissions are significantly increased through the induced SP coupling of the Ag nano-plates. When both GQD and RQD exist and are closely spaced in a sample, the energy transfer processes of emission-reabsorption and Förster resonance energy transfer from GQD into RQD occur, leading to the increase (decrease) in the MB of green (red) light. With SP coupling, the MB of a mixed light is significantly enhanced.

Förster resonance energy transfer in surface plasmon coupled color conversion processes of colloidal quantum dots.

Förster resonance energy transfer (FRET) from a green-emitting quantum dot (GQD) into a red-emitting quantum dot (RQD) is an important mechanism in a multiple-color conversion process, particularly under the surface plasmon (SP) coupling condition for enhancing color conversion efficiency. Here, the dependencies of FRET efficiency on the relative concentrations of GQD and RQD in their mixtures and their surface molecule coatings for controlling surface charges are studied. Also, the SP coupling effects induced by two kinds of Ag nanoparticles on the emission behaviors of GQD and RQD are demonstrated, particularly when FRET is involved in the coupling process. FRET efficiency is reduced under the SP coupling condition. SP coupling can enhance the color conversion efficiency of either GQD or RQD. The combination of SP coupling and FRET can be used for controlling the relative converted light intensities in a multiple-color conversion process.

Development and validation of a preoperative nomogram for predicting positive surgical margins after laparoscopic radical prostatectomy.

BACKGROUND: Positive surgical margins are independent risk factor for biochemical recurrence, local recurrence, and distant metastasis after radical prostatectomy. However, limited predictive tools are available. This study aimed to develop and validate a preoperative nomogram for predicting positive surgical margins after laparoscopic radical prostatectomy (LRP). METHODS: From January 2010 to March 2016, a total of 418 patients who underwent LRP without receiving neoadjuvant therapy at Peking University Third Hospital were retrospectively involved in this study. Clinical and pathological results of each patient were collected for further analysis. Univariable and multivariable logistic regression (backward stepwise method) were used for the nomogram development. The concordance index (CI), calibration curve analysis and decision curve analysis were used to evaluate the performance of our model. RESULTS: Of 418 patients involved in this study, 142 patients (34.0%) had a positive surgical margin on final pathology. Based on the backward selection, four variables were included in the final multivariable regression model, including the percentage of positive cores in preoperative biopsy, clinical stage, free prostate specific antigen (fPSA)/total PSA (tPSA), and age. A nomogram was developed using these four variables. The concordance index (C-index) of the nomogram was 0.722 in the development cohort and 0.700 in the bootstrap validations. The bias-corrected calibration plot showed a limited departure from the ideal line with a mean absolute error of 2.0%. In decision curve analyses, the nomogram showed net benefits in the range from 0.2 to 0.7. CONCLUSION: A nomogram to predict positive surgical margins after LRP was developed and validated, which could help urologists plan surgical procedures.

Application of the astigmatic method to the thickness measurement of glass substrates.

We developed a high accuracy thickness measurement system for glass substrates based on the optical design of the astigmatic method. The astigmatic optical system includes a laser diode, a cylindrical lens, a convex lens, and a quadrant detector. This method measures the astigmatic focusing error signal induced from the measured glass placed in the astigmatic optical system. The astigmatic focusing error signal is converted into the thickness of the glass substrate. The proposed glass thickness measurement system is verified by using a coordinate measuring machine (CMM). The accuracy of the proposed system is 0.2 microm, with a standard deviation of 0.7 microm within the thickness measuring range of 1.2 mm.